Electromagnetically-operated fuel injection valve

An electromagnetically-operated fuel injection valve has a magnetic circuit comprising a valve casing, a stator core on which an electromagnetic coil is wound, an armature core, and an air gap between the stator core and the armature core. At least one of the valve casing, the stator core and the armature core is so configuared that the magnetic flux passing therethrough is saturated substantially at the time the armature core is fully attracted to inject fuel. A magnetic restrictor at which the cross-sectional area for the magnetic flux is reduced than that at the other portion is provided at least at a portion of the valve casing, the stator core and the armature core so that the magnetic flux is saturated thereat substantially at the time the armature core is attracted fully.

BACKGROUND OF THE INVENTION 
The present invention relates to an electromagnetically-operated fuel 
injection valve for use in an electronically-controlled fuel injection 
system. 
In an electronically-controlled fuel injection system for an internal 
combustion engine of an automotive vehicle, an 
electromagnetically-operated fuel injection valve has been used. 
As disclosed in Kamai et al U.S. Pat. No. 4,331,317 assigned to the same 
assignee of the present application, for instance, the fuel injection 
valve generally has an electromagnetic coil wound on a stator core in a 
valve casing, an armature core integrally connected with a valve needle 
for opening and closing an injection port, and a spring disposed between 
the stator core and the armature core for biasing the valve needle to 
close the injection port. While the electromagnetic coil is energized, a 
magnetic circuit is formed through the stator core, the valve casing, the 
armature core and an air gap between the stator core and the armature 
core, and the armature core is attracted against the biasing force of the 
spring so that the valve needle integral with the armature core opens the 
injection port for metering fuel. 
In the magnetic circuit, the minimum cross-sectional area for the magnetic 
flux is formed at a portion where the bottom of the stator core and the 
top of the armature core face with the air gap therebetween and the 
cross-sectional area for the magnetic flux in the other portions of the 
magnetic circuit is made larger than the minimum cross-sectional area. As 
a result, while the electromagnetic coil is kept energized, the electric 
current actually flowing through the electromagnetic coil and the 
resulting electromagnetic force increase gradually until the magnetic 
saturation occurs, even after the armature core and the valve needle are 
fully attracted to open the injection port fully after a valve opening 
response delay. Since the time period the electromagnetic coil is kept 
energized is varied in proportion to the required quantity of fuel, the 
electric current having been flowing through the electromagnetic coil and 
the electromagnetic force generated just before the electromagnetic coil 
is deenergized is dependent on the time period the electromagnetic coil 
has been energized. As a result, a valve closing response delay in which 
the valve needle is returned to the fully closed position from the fully 
open position in response to the deenergization of the electromagnetic 
coil is varied in dependence on the energization time period. Therefore, 
even if the valve opening response delay is substantially constant, 
linearity between the energization time period and the metered quantity of 
fuel cannot be assured. 
SUMMARY OF THE INVENTION 
It is a primary object of the invention to provide an 
electromagnetically-operated fuel injection valve capable of assuring 
substantial linearity between the energization time period and the metered 
quantity of fuel. 
It is a further object of the invention to provide an 
electromagnetically-operated fuel injection valve the valve closing 
response delay of which is maintained substantially constant. 
It is a still further object of the invention to provide an 
electromagnetically-operated fuel injection valve the magnetic circuit of 
which magnetically saturates substantially as soon as an armature core is 
fully attracted. 
The electromagnetically operated fuel injection valve according to the 
present invention has a magnetic circuit comprising a valve casing, a 
stator core on which an electromagnetic coil is wound, an armature core 
integral with a valve needle, and an air gap between the stator core and 
the armature core. At least one of the valve casing, the stator core and 
the armature core is so configured that the magnetic flux passing 
therethrough is saturated substantially at the time the armature core is 
fully attracted.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The present invention will be described in more detail hereinunder. 
In FIG. 1 showing a first embodiment, numeral 1 designates a valve casing 
comprising a first body 2 and a second body 3. The bottom of the body 2 is 
bent to be firmly connected to the body 3. The body 2 is made of a 
conventional magnetic material such as ferrite having a low magnetic 
saturation characteristic. The body 2 is shaped generally cylindrically 
and has a magnetic restrictor 23 at which the cross-sectional area for the 
magnetic flux is reduced by the circumferentially formed groove. A cover 4 
is presently fixed to the lower portion of the body 3. 
An electromagnetic coil 5 connected to an electrical terminal 6 is provided 
in the first body 2 so that, when an electric pulse voltage is applied to 
the terminal 6 by an electronic control unit 7, the electromagnetic coil 5 
is energized to generate magnetic flux. 
A stator core 8 having a longitudinal inner space is fixedly provided in 
the body 2. The electromagnetic coil 5 is carried on the stator core 8 by 
way of a resin bobbin. The stator core 8 is made of the same magnetic 
material as the body 2. At the top end of the stator core 8, a connector 
portion 16 in which a fuel filter 17 is provided is formed to be connected 
to a fuel pipe 24. 
An armature core 9 is movably provided in the body 2 to face the bottom end 
of the stator core 8 leaving an air gap therebetween. The armature core 9 
is made of the same magnetic material as the body 2 and the stator core 8. 
A valve needle 11 is fitted, by caulking, to the bottom portion of the 
stator core 8 to be movable therewith. The top end portion of the valve 
needle 11 fitted within the through hole of the armature core 9 is formed 
with a pair of flat surfaces for allowing fuel flow therethrough. A coiled 
spring 10 is provided between the armature core 9 and the stator core 8 to 
downwardly bias the armature core 9 and the valve needle 11. The top end 
of the coiled spring 10 is received by the bottom end of the fuel pipe 24 
fitted in the stator core 8. The valve needle 11 which is axially movable 
within longitudinal inner spaces of the bodies 2 and 3 is provided with a 
conical head at the bottom end portion thereof. On the other hand, a valve 
seat 19 which receives the conical head of the valve needle 11 and a fuel 
injection port 20 which is in communication with a fuel chamber 18 are 
provided at the bottom of the body 3. The valve needle 11 has a stopper 21 
and a stopper 22 is inserted between the bodies 2 and 3, thus limiting the 
upward movement of the valve needle 11. 
The connector portion 16 is connected to a fuel tank 12 through a fuel 
filter 14 and a fuel pump 13 in one way and through a pressure regulator 
15 in the other way. 
While no electric pulse voltage is applied to the electromagnetic coil 5 by 
the control unit 7, the armature core 9 biased downward by the coiled 
spring 10 keeps the conical head of the valve needle 11 to seat on the 
valve seat 19 of the body 3 so that no fuel to be injected from the 
injection port 20 is metered. While the electric pulse voltage is applied 
to the electromagnetic coil 5 by the control unit 7, on the other hand, 
the electromagnetic coil 5 is energized to generate the magnetic flux 
which circularly passes a magnetic circuit comprising the body 2, the 
stator core 8, the armature core 9 and the air gap between the stator core 
8 and the armature core 9 as shown by the arrows in the figure. As a 
result, the magnetic force is generated between the stator core 8 and the 
armature core 9 and the armature core 9 is attracted upward against the 
biasing force of the coiled spring 10. As the armature core 9 is attracted 
toward the stator core 10, the conical head of the valve needle 11 leaves 
the valve seat 19 so that fuel flowing through the fuel pipe 24, the 
armature core 9 and through the outer space of the valve needle 11 and 
being accumulated in the fuel chamber 18 is injected through the injection 
port 20. 
When the electric pulse voltage applied to the electromagnetic coil 5 is 
stopped, the electromagnetic force between the stator core 8 and the 
armature core 9 dissappears and the conical head of the valve needle 11 is 
pushed down by the coiled spring 10 to seat on the valve seat 19 so that 
fuel injection is stopped. 
It should be noted, in the above-described first embodiment, that the 
magnetic restrictor 23 or the narrowed cross-sectional area is formed so 
as to limit the magnetic flux passing therethrough to the magnetic flux 
passing between the stator core 8 and the armature core 9 at the time the 
armature core 9 is fully attracted toward the stator core 8. In other 
words, the magnetic restrictor 23 effectuates magnetic saturation in the 
magnetic circuit as soon as the valve needle 11 is fully lifted. The 
magnetic restrictor 23 must be determined in relation to the magnetic 
material. When the magnetic material used has a high magnetic saturation 
characteristic, the cross-sectional area at the magnetic restrictor 23 
must be decreased. When the magnetic material used has a low magnetic 
saturation characteristic, the cross-sectional area at the magnetic 
restrictor 23 must be increased. 
The operational mode of the above-described embodiment will be described 
further with reference to FIG. 2 in which solid lines show characteristics 
of the first embodiment and dotted lines show characteristics of the 
conventional fuel injection valve having no magnetic restrictor. 
As shown in FIG. 2, as soon as the electric pulse voltage having a time 
period t1 is applied to the electromagnetic coil 5, the electric current 
passing through the coil 5 gradually increases because of the inductance 
of the coil 5 and hence the magnetic force generated also gradually 
increases. After a valve opening response delay To, the magnetic force 
attains a certain level at which the valve needle 11 is lifted to the 
uppermost position to fully open the injection port 20 so that fuel 
metering is initiated. When the valve needle 11 is lifted to the uppermost 
position, the air gap between the stator core 8 and the armature core 9 is 
reduced to the minimum and the magnetic resistance in the magnetic circuit 
is reduced to the minimum. With this minimum magnetic resistance, the coil 
current in the magnetic coil 5 increases thereafter. However, the magnetic 
flux in the magnetic circuit is saturated by the magnetic restrictor 23 so 
that the magnetic force is kept substantially unchanged relative to the 
increase in the coil current as opposed to the conventional one in which 
the magnetic force is proportional to the coil current. When the electric 
pulse voltage applied to the magnetic coil 5 disappears, the coil current 
and the magnetic force decreases gradually. When the magnetic force is 
reduced to zero, the valve needle is returned to the lowermost position to 
close the injection port 20 to terminate metering fuel. Thus the valve 
needle 11 is kept open for a valve closing response delay Tc even after 
the electric pulse voltage disappears irrespective of the time period t1 
of the electric pulse voltage, the valve closing response delay Tc is 
unchanged irrespective of the time period t1 of the electric pulse 
voltage. As a result, the quantity of fuel injected through the injection 
port 20 is made proportional to the time period t1 of the electric pulse 
voltage as opposed to the conventional one in which the quantity of fuel 
injected is varied in dependence on the varied valve closing response 
delay Tc. 
FIGS. 3 and 4 show a second and third embodiments, respectively, in which 
same reference numerals are used to designate the same or equivalent 
portions as in the first embodiment shown in FIG. 1. 
According to the second embodiment shown in FIG. 3, the magnetic restrictor 
23 the cross-sectional area of which is smaller than the facing area 
between the bottom end of the stator core 8 and the top end of the 
armature core 9 is provided on the stator core 8 by a circumferentially 
formed outer groove. According to the second embodiment, the magnetic 
restrictor 23 is not provided on the body 2 but provided on the stator 
core 8. Therefore, the mechanical strength of the body 2 which is fixedly 
attached to an internal combustion engine (not shown) is assured. 
In the third embodiment shown in FIG. 4, the magnetic restrictor 23 is 
provided in the armature core 9 by forming a widened inner hole 91. 
According to the third embodiment, the weight of the armature core 9 is 
decreased and therefore the valve opening response delay To and the valve 
closing response delay Tc are made shorter. 
The present invention having been described hereinabove is not limited to 
the specific embodiments but may be modified in many ways without 
departing from the spirit of the invention.