Fuel injector

Details Fuel injector Fuel injector

1999-09-14

2001-07-24

Morris, Lesley D. (Department: 3752)

Fluid sprinkling, spraying, and diffusing

With system fluid relief or return to supply

C239S585100

Reexamination Certificate

active

06264116

ABSTRACT:

This invention relates to a fuel injector for use in delivering fuel under high pressure to a cylinder or combustion space of an associated engine. In particular, the invention relates to a fuel injector of the type in which the fuel pressure at the commencement of injection can be controlled independently of the timing of fuel injection. The invention also relates to a method of operation of such an injector.
It is known, in a unit injector arrangement, to use separately actuated spill or drain valves and injection control valves to permit the timing of injection and the injection pressure to be controlled independently. It is also known to control the spill or drain valve and the injection control valve of a unit injector using a single actuator including an armature common to both valves. In a typical arrangement, when injection is to be terminated the injection control valve is closed to permit the fuel pressure within a control chamber to rise, the increased fuel pressure within the control chamber forcing the injector needle into engagement with its seating to terminate injection. Forcing the needle into engagement with its seating against a relatively high injection pressure in this manner can cause the generation of undesirably high smoke and particulate emissions. It is an object of the invention to provide a fuel injector in which this disadvantage is overcome.
According to the present invention there is provided a fuel injector comprising a valve needle biased by a spring into engagement with a seating, a surface associated with the needle being exposed to the fuel pressure within a control chamber, restricted communication means providing a restricted flow path between a supply passage and the control chamber, a drain valve controlling communication between the supply passage and a low pressure reservoir, an injection control valve controlling communication between the control chamber and the low pressure reservoir, the drain valve and the injection control valve being moveable under the control of a single electromagnetic actuator including an armature common to both valves, wherein the injection control valve, the drain valve and the actuator are arranged such that at rest, the injection control valve and the drain valve are open, when the actuator is energized to a first, relatively low energization level the drain valve is closed and the injection control valve is open, and when the actuator is energized to a second, higher energization level, the drain valve and the injection control valve are both closed.
In such an arrangement, injection is terminated by de-energizing the actuator, thereby allowing the drain valve to open. As, immediately prior to the drain valve opening, the injection control valve is already open, termination of injection occurs under the action of the spring biasing of the injector needle against a reduced injection pressure rather than due to the increase of fuel pressure within the control chamber. The risk of production of excessive smoke and particulates emissions is reduced.
The responsiveness of the injector may be improved by reversing the polarity of the connections of the supply to the actuator when the energization level of the actuator is to be reduced rather than simply allowing the actuator current to decay.
The injector conveniently takes the form of a unit pump/injector.
According to another aspect of the invention there is provided a method of operating an injector of the type defined hereinbefore comprising the steps of:
energizing the actuator to its second, higher level to close the drain and injection control valves when the pressurization of fuel is to commence;
allowing the energization level of the actuator to fall to its first level to allow the injection control valve to open when injection is to commence; and
de-energizing the actuator to allow the drain valve to open when injection is to terminate.
The step of allowing the energization level of the actuator to fall may include reversing the polarity of the connections between a supply and the actuator.


REFERENCES:
patent: 5042718 (1991-08-01), Bergmann et al.
patent: 5531382 (1996-07-01), Buckley et al.
patent: 5628293 (1997-05-01), Gibson et al.
patent: 5660331 (1997-08-01), Cooke
patent: 5860597 (1999-01-01), Tarr
patent: 5967413 (1999-10-01), Tian
patent: 6027047 (2000-02-01), Augustin
patent: 0 823 550 A1 (1998-02-01), None

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