Structure of fuel injector adjustable in fuel jet...

Fluid sprinkling – spraying – and diffusing – Processes – Of fuel injection

Reexamination Certificate

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C239S088000, C239S096000, C239S533500, C239S533600, C239S533800, C239S580000, C239S585100

Reexamination Certificate

active

06409094

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Technical Field of the Invention
The present invention relates generally to an improved structure of a fuel injector capable of adjusting fuel jet characteristics such as the quantity of a fuel jetting out of the fuel injector and fuel injection time lag after assembled.
2. Background Art
Fuel injectors are known in the art which are designed to control the fuel pressure in a pressure chamber formed in a nozzle body which acts on a valve for closing an injection nozzle. For moving the valve, the fuel injector controls a balance of a valve-opening pressure developed by the fuel pressure supplied to a fuel sump, a valve-closing pressure developed by the fuel pressure in the pressure chamber, and a spring pressure acting on the valve to close the nozzle. Within the pressure chamber, a fuel drain valve is installed. The regulation of the fuel pressure in the pressure chamber is accomplished by opening and closing the fuel drain valve.
Japanese Patent No. 2599281 discloses such a fuel injector which is illustrated in FIG.
8
.
A constant pressure of fuel is supplied to a pressure control chamber
211
and a fuel sump
216
. A valve hole
207
leading to the pressure chamber
211
is closed by a control valve
206
. When the sum of the fuel pressure in the control pressure chamber
211
working to urge the control valve
206
in a valve-opening direction and the attractive force produced by an electromagnet
213
attracting an armature
205
overcomes the spring pressure of a coil spring
203
urging the control valve
206
in a valve-closing direction, it will cause the control valve
206
to be lifted up to open the valve hole
207
, so that the fuel pressure in the control pressure chamber
211
drains to a magnet chamber
215
through a valve chamber
217
and holes formed in a yoke
212
, thereby resulting in a drop in fuel pressure within the control pressure chamber
211
. This causes the sum of fuel pressure in the fuel sump
216
urging a nozzle valve
200
in a spray hole-opening direction and the pressure produced by a coil spring
218
urging the nozzle valve
200
in a spray hole-closing direction to overcome the fuel pressure in the control pressure chamber
211
, thereby lifting the nozzle valve
200
upward. When the electromagnet
213
is deenergized, it will cause the control valve
206
to close the valve hole
207
, thereby resulting in an increase in fuel pressure within the control pressure chamber
211
. This causes the nozzle valve
200
to be moved downward to close the spray hole. The injection timing, therefore, has a correlation with the time of lift of the control valve
206
. The quantity of fuel injected has a correlation with the length of time the valve hole
207
is opened.
The above fuel injector, however, has a problem that it is difficult to adjust the quantity of fuel injected after the fuel injector is assembled. The reason for this will be discussed below.
The lift of the control valve
206
undergoes a time lag between application of a drive pulse signal to the electromagnet
213
and action of a valve-lifting force on the control valve
206
. The injection delay depends upon the spring load produced by the spring
203
on the control valve
206
in the valve-closing direction. The spring load is determined by the degree to which an adjusting screw
202
is fastened. It is, however, impossible to change the fastening degree of the adjusting screw
202
after the fuel injector is assembled, thus resulting in a difficulty in adjusting the time lag and the action of the valve-lifting force on the control valve
206
.
If the width of the drive pulse signal applied to the electromagnet
213
is constant, and the fuel pressure supplied to the fuel injector is also constant, the opening duration of the valve hole
207
depends upon a time delay between rising of the drive pulse signal and the time the control valve starts to be lifted and a time delay between falling of the drive pulse signal and the time the control valve closes the valve hole
207
. The valve lift time delay depends upon the spring load of the spring
203
and, thus, impossible to regulate after the fuel injector is assembled. The valve closing time delay depends upon the amount of lift of the control valve
206
and the spring load of the spring
203
. A maximum amount of lift of the control valve
206
is determined by an air gap between the stator or yoke
204
and the armature
205
. It is, however, impossible to adjust the spring load for the same reason as described above. The electromagnet
213
and the valve hole
207
are both restrained by a guide member
208
from moving. The guide member
208
is held between a nozzle body
209
and a control body
214
. The air gap between the yoke
204
and the armature
205
is a function of the distance between the valve hole
207
and the yoke
204
. It is, thus, impossible to change the amount of lift of the control valve
206
after the fuel injector is assembled. For these reasons, the opening duration of the valve hole
207
cannot be adjusted after the assembly of the fuel injector, thus resulting in a difficulty in regulating the quantity of fuel to be injected into the engine.
Accordingly, the regulation of the quantity of fuel injected should be accomplished by repeating a series of operations: inspection of the quantity of fuel injected, disassembly of the fuel injector, turning of the adjusting screw
202
, and/or replacement of the guide member
208
. This, however, results in a great reduction in productivity. It is also impossible to eliminate a difference in quantity of fuel injected between fuel injectors arising from a difference in size between spray holes.
Further, it is impossible to drain the fuel in the control pressure chamber
211
from a drain passage
201
along a longitudinal center line of the fuel injector. The fuel is, in practice, discharged to the drain passage
201
from the valve hole
207
through the magnet chamber
215
surrounding the electromagnet
213
, thus resulting in an increase in size of the fuel injector in a widthwise-direction thereof.
SUMMARY OF THE INVENTION
It is therefore a principal object of the invention to avoid the disadvantages of the prior art.
It is another object of the invention to provide a compact structure of a fuel injector which is capable of adjusting a fuel jet characteristic such as the quantity of a fuel jet to a target one after the fuel injector is assembled.
According to one aspect of the invention, there is provided an improved structure of a fuel injector capable of adjusting a fuel jet characteristic after assembled. The fuel injector comprises: (a) a nozzle having formed therein a spray hole from which fuel is sprayed; (b) a nozzle valve selectively opening and closing the spray hole; (c) an injector body supporting therein the nozzle valve slidably, the injector body having formed therein a fuel sump supplied with the fuel from an inlet formed in the injector body to produce fuel pressure urging the nozzle valve in a spray hole-opening direction, a pressure chamber supplied with the fuel from the inlet to produce fuel pressure urging the nozzle valve in a spray hole-closing direction, and a valve hole establishing fluid communication between the pressure chamber and a drain port formed in the injector body; (d) a control valve selectively opening and closing the valve hole formed in the injector body; (e) a first urging mechanism urging the control valve in a valve hole-closing direction for closing the valve hole to block the fluid communication between the pressure chamber and the drain port; (f) a control valve moving mechanism made up of a stationary portion and a movable portion, the stationary portion including a stator and a coil, the movable portion including an armature which is connected fixedly to the control valve and spaced from the stator through a given air gap, the coil being energized electrically to produce an attractive force through the stator for attracting the armature to move the control valve in a

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