Fuel Injector

Details Fuel Injector Fuel Injector

1999-02-16

2001-03-06

Kashnikow, Andres (Department: 3752)

Fluid sprinkling, spraying, and diffusing

Unitary injection nozzle and pump or accumulator plunger

C239S090000, C239S093000, C239S095000, C239S533200, C239S102200

Reexamination Certificate

active

06196472

ABSTRACT:

This invention relates to a fuel injector for use in supplying fuel under pressure to an internal combustion engine. In particular, the invention relates to a fuel injector including a valve needle moveable under the control of a piezoelectric actuator.
It is desirable to use a piezoelectric actuator of the type which expands when energized to control the operation of a fuel injector. Common rail injectors usually require retraction of a valve needle from its seating to allow injection of fuel. It is an object of the invention to provide a fuel injector arranged to be actuated by a piezoelectric actuator of the type which expands when energized.
In order to minimize the stack height of the piezoelectric actuator of such an injector, it is desirable to provide an arrangement whereby the expansion and contraction of the piezoelectric actuator, in use, is amplified resulting in movement of the valve needle of the injector through a distance greater than the distance over which an end part of the actuator moves.
According to an aspect of the invention there is provided a fuel injector comprising a valve needle slidable within a bore and engageable with a seating to control the supply of fuel to an outlet opening, an end surface of the valve needle being exposed to the fuel pressure within a control chamber defined, in part, by a piston member moveable under the influence of a piezoelectric actuator, wherein the control chamber is supplied with fuel under pressure, in use, through a restricted flow path.
The restricted flow path conveniently takes the form of a controlled leakage path between the valve needle and the bore. Alternatively, a separate drilling may be provided to permit the supply of fuel to the control chamber at a restricted rate.
The supply of fuel to the control chamber, in use, acts to urge the needle towards its seating thus preventing continuous injection in the event of failure of the actuator or the associated drive circuit.
According to another aspect of the invention there is provided a fuel injector comprising a valve needle slidable within a bore and engageable with a seating to control the supply of fuel to an outlet opening, a surface associated with the valve needle being exposed to the fuel pressure within a control chamber defined, in part, by a first piston member moveable under the influence of a piezoelectric actuator, wherein the effective area of the first piston member exposed to the fuel pressure within the control chamber is greater than the corresponding area of the said surface associated with the valve needle.
Such an arrangement is advantageous in that the travel of the valve needle is greater than the movement of the piston, thus a greater level of valve needle travel can be achieved for a piezoelectric actuator of a given stack height.
The injector preferably further comprises a shield member shielding part of the valve needle from the fuel pressure within the control chamber. The shield member may comprise a second piston member located within a bore provided in the valve needle. Alternatively, the shield member may take the form of a sleeve through which part of the valve needle extends. The shield member may be moveable with the first piston member, or may alternatively be fixed relative to the body of the injector.
According to a further aspect of the invention there is provided a drive circuit for a piezoelectrically actuated injector, the drive circuit including at least one by-pass resistor arranged to ensure that, upon switching off of an associated engine, the actuator of the injector remains actuated for a sufficiently long duration to allow the fuel pressure applied to the injector to decay.


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patent: 5803361 (1998-09-01), Horiuchi et al.
patent: 5860597 (1999-01-01), Tarr
patent: 197 02 066 (1998-07-01), None
patent: 0 889 230 (1999-01-01), None

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