The present invention relates to an electromagnetically
actuated fuel injector.
An electromagnetic fuel injector normally comprises a tubular
supporting body having a central channel, which acts as a fuel conduit and terminates
in an injection nozzle regulated by an injection valve controlled by an electromagnetic
actuator. The injection valve has a pin connected rigidly to a movable armature
of the electromagnetic actuator, and which is moved by the electromagnetic actuator
between a closed position and an open position respectively closing and opening
the injection nozzle in opposition to a spring which keeps the pin in the closed
One example of an electromagnetic fuel injector of the
above type is described in Patent US-6027050-A1, which relates to a fuel injector
having a pin which cooperates at one end with a valve seat, and is integral at the
opposite end with a movable armature of an electromagnetic actuator; the pin is
guided by the armature at the top, and at the bottom by the end portion of the pin
sliding inside a guide portion of the valve seat.
Known electromagnetic fuel injectors of the above type
are widely used, by combining good performance and low cost. Since injectors with
an electromagnetically actuated pin, however, are unable to operate at very high
fuel pressures, injectors with a hydraulically operated pin have been proposed,
i.e. in which movement of the pin from the closed to the open position, in opposition
to the spring, is produced by hydraulic forces. Examples of such injectors are described
in Patent Applications EP-1036932-A2, EP-0921302-A2, and WO-0129395-A1.
Though of good dynamic performance and capable of operating
at very high fuel pressures, injectors with a hydraulically actuated pin are complicated
and expensive to produce, by requiring a hydraulic circuit with a piezoelectrically
or electromagnetically actuated control valve. Moreover, there is always a certain
amount of backflow of fuel, which is drained at ambient pressure, and which has
the negative effects of constituting a loss of energy, and of tending to heat the
When assembled in an injection system, the injector is
connected to a pressurized-fuel feed conduit. More specifically, the tubular supporting
body of the injector is connected in fluidtight manner to the feed conduit to connect
the central channel of the supporting body hydraulically to the feed conduit. The
fluidtight connection is normally made using a connector, which provides for a conical
connection with no elastic seals, i.e. an inclined surface of the supporting body
is kept pressed against a corresponding inclined surface of the connector with no
elastic seal in between. However, to ensure long-term sealing of such connections,
even in the presence of continuous vibration (typical of an internal combustion
engine), the component parts, particularly the inclined surfaces pressed against
each other, call for extremely precise machining, and as such are time-consuming
and expensive to produce.
It is an object of the present invention to provide an
electromagnetically actuated fuel injector designed to eliminate the aforementioned
drawbacks, and which, in particular, is cheap and easy to produce.
According to the present invention, there is provided an
electromagnetically actuated fuel injector, as recited in the accompanying Claims.
A number of non-limiting embodiments of the present invention
will be described by way of example with reference to the accompanying drawings,
- Figure 1 shows a schematic, partly sectioned, side view of a fuel injector in
accordance with the present invention;
- Figure 2 shows a larger-scale view of an injection valve of the Figure 1 injector;
- Figure 3 shows a larger-scale view of a connecting device fitted to the Figure
- Figure 4 shows an alternative embodiment of the Figure 3 connecting device.
Number 1 in Figure 1 indicates as a whole a fuel injector,
which is cylindrically symmetrical about a longitudinal axis 2, and is controlled
to inject fuel from an injection nozzle 3. Injector 1 comprises a cylindrical tubular
supporting body 4 varying in section along longitudinal axis 2, and having a central
channel 5 extending the full length of supporting body 4 to feed pressurized fuel
to injection nozzle 3. Supporting body 4 houses an electromagnetic actuator 6 in
a top portion, and an injection valve 7 in a bottom portion. In actual use, injection
valve 7 is activated by electromagnetic actuator 6 to regulate fuel flow through
injection nozzle 3, which is formed at injection valve 7.
Supporting body 4 is formed by connection of a one-piece
tubular top member 8, housing electromagnetic actuator 6, to a one-piece tubular
bottom member 9, housing injection valve 7. Tubular top member 8 preferably comprises
a cylindrical, internally threaded seat for receiving a threaded portion of tubular
bottom member 9. A one-piece cylindrical sleeve 10, preferably made of plastic material,
such as PEEK 30 CF, may be fitted about part of tubular top member 8 and part of
tubular bottom member 9 to relieve tubular bottom member 9 of the axial and transverse
loads (e.g. tightening stress) to which injector 1 is subjected.
Electromagnetic actuator 6 comprises an electromagnet 11
housed in a fixed position inside supporting body 4, and which, when excited, moves
an armature 12 of ferromagnetic material along axis 2 from a closed position to
an open position to open injection valve 7 in opposition to a spring 13 which keeps
armature 12 in the closed position closing injection valve 7. Electromagnet 11 comprises
a dry coil 14 powered electrically by an electronic control unit (not shown) and
located outside supporting body 4; and a magnetic core 15 housed inside supporting
body 4 and having a central hole 16 to permit fuel flow to injection nozzle 3. A
cylindrical tubular retaining body 17 is fitted in a fixed position inside central
hole 16 in magnetic core 15 to permit fuel flow to injection nozzle 3 and to keep
spring 13 pressed against armature 12. Magnetic core 15 is preferably connected
to supporting body 4 by an annular weld inside supporting body 4.
Coil 14 of electromagnet 11 is housed inside a tubular
seating body 18, which is closed at the bottom, surrounds supporting body 4, and
is welded to supporting body 4 by an annular weld. At the top, seating body 18 is
closed by an annular plug 19 welded to seating body 18 to isolate coil 14 inside
seating body 18. It is important to note that, by virtue of its location, coil 14
dissipates considerable heat, and is isolated from the fuel and so unaffected by
the mechanical effect and chemical aggression produced by the pressurized fuel.
Armature 12 forms part of a movable assembly, which also
comprises a shutter or pin 20 having a top portion integral with armature 12, and
a bottom portion cooperating with a valve seat 21 (Figure 2) of injection valve
7 to regulate fuel flow through injection nozzle 3 in known manner.
As shown in Figure 2, valve seat 21 is defined by a disk-shaped
sealing member 22, which closes the bottom of central channel 5 of supporting body
4 in fluidtight manner, and through which injection nozzle 3 extends. A tubular
guide member 23 extends upwards from disk-shaped sealing member 22, houses pin 20
to define a bottom guide of pin 20, and has an outside diameter substantially equal
to the inside diameter of central channel 5 of supporting body 4.
Pin 20 terminates with a substantially spherical shutter
head 24, which rests in fluidtight manner on valve seat 21. Shutter head 24 also
rests in sliding manner against a cylindrical inner surface 25 of guide member 23,
by which it is guided in its movement along longitudinal axis 2. Recesses 26 (only
one shown in Figure 2) are formed in shutter head 24 to define, between each recess
26 and cylindrical inner surface 25 of guide member 23, a fuel flow passage to injection
nozzle 3. In a preferred embodiment shown in Figure 2, injection nozzle 3 is defined
by a number of through holes 27 extending from a hemispherical chamber 28 formed
downstream from valve seat 21.
As shown in Figure 1, armature 12 is a one-piece body,
and comprises an annular member 29; and a disk-shaped member 30, which closes the
underside of annular member 29, and in turn comprises a central through hole for
receiving a top portion of pin 20, and a number of peripheral through holes (only
two shown in Figure 1) to permit fuel flow to injection nozzle 3. A central portion
of disk-shaped member 30 is shaped to receive and hold in position a bottom end
of spring 13. Pin 20 is preferably made integral with disk-shaped member 30 of armature
12 by an annular weld.
The outside diameter of annular member 29 of armature 12
is substantially equal to the inside diameter of the corresponding portion of central
channel 5 of supporting body 4, so that armature 12 can slide with respect to supporting
body 4 along longitudinal axis 2, but is prevented from moving crosswise to longitudinal
axis 2 with respect to supporting body 4. Pin 20 being connected rigidly to armature
12, armature 12 therefore also acts as a top guide for pin 20, which is therefore
guided at the top by armature 12 and at the bottom by guide member 23.
In an alternative embodiment not shown, a bounce-damping
device is connected to the underside face of disk-shaped member 30 of armature 12
to reduce bounce of shutter head 24 of pin 20 on valve seat 21 when pin 20 moves
from the open position to the closed position closing injection valve 7.
In actual use, when electromagnet 11 is deenergized, armature
12 is not attracted by magnetic core 15, and the elastic force of spring 13 pushes
armature 12, together with pin 20, downwards, so that shutter head 24 of pin 20
is pressed against valve seat 21 of injection valve 7 to isolate injection nozzle
3 from the pressurized fuel. Conversely, when electromagnet 11 is energized, armature
12 is attracted magnetically by magnetic coil 15 in opposition to the elastic force
of spring 13, and armature 12, together with pin 20, moves up into contact with
magnetic core 15, so that shutter head 24 of pin 20 is lifted off valve seat 21
of injection valve 7, thus permitting pressurized-fuel flow through injection nozzle
As shown clearly in Figure 1, tubular bottom member 9 is
much longer than tubular top member 8, and houses almost the whole of pin 20, which
is the mechanical member responsible for opening and closing injection valve 7.
To avoid the negative effects produced by thermal expansion, both tubular bottom
member 9 and pin 20 are made of a low-thermal-expansion alloy, in particular INVAR
36. Cylindrical sleeve 10, on the other hand, performs purely mechanical functions,
to relieve tubular bottom member 9 of the axial and transverse loads to which injector
1 is subjected in use, and is therefore made of ordinary stainless steel.
Tubular top member 8 is preferably made of high-tensile
stainless steel with poor magnetic characteristics (i.e. nonmagnetic, and therefore
of low magnetic permeability comparable to that of air). An iron-cobalt alloy, such
as hardened and tempered ISI 440C, may be used, for example. Seating body 18, annular
plug 19, magnetic core 15, and armature 12 (or at least tubular member 9 of armature
12) are made of magnetic stainless steel (i.e. with a much higher magnetic permeability
than air), such as VACUFLUX 50.
In an alternative embodiment not shown, supporting body
4 is formed in one piece and made entirely of high-tensile stainless steel with
poor magnetic characteristics.
Injector 1 as described above is cheap and easy to produce,
by being formed by connecting a small number of parts, each of which is cylindrically
symmetrical and therefore easy to produce by means of standard, easily automated
turning operations involving no dedicated tooling. Moreover, simulation and testing
have shown injector 1 as described above to be capable of operating at very high
fuel pressures (close to 1000 bars) while still maintaining excellent dynamic performance
(i.e. precise injection times).
As shown in Figures 3 and 4, supporting body 4 of injector
1 is connected to a pressurized-fuel feed conduit 31 by means of a connector 32.
More specifically, supporting body 4 is connected in fluidtight manner to feed conduit
31 to connect central channel 5 of supporting body 4 hydraulically to feed conduit
Connector 32 is cylindrically symmetrical about longitudinal
axis 2, and comprises a cylindrical top member 33, which is substantially equal
in outside diameter to the inside diameter of feed conduit 31, and has a threaded
outer end portion which screws inside feed conduit 31. Connector 32 also comprises
a central member 34 larger in outside diameter than top member 33 and terminating
with a truncated-cone-shaped surface 35; and a cylindrical bottom member 36 smaller
in outside diameter than the inside diameter of central channel 5 of supporting
body 4, and which is located inside central channel 5. For this purpose, the top
end of supporting body 4 has a truncated-cone-shaped surface 37, which is positioned
contacting truncated-cone-shaped surface 35 of central member 34 of connector 32.
To keep connector 32 pressed against supporting body 4,
an annular fastening member 38 is screwed to a threaded outer surface 39 of supporting
body 4 so as to contact, with a given pressure, an annular top surface 40 of central
member 34 of connector 32.
An elastic annular seal 43 is fitted between an outer surface
41 of bottom member 36 and an inner surface 42 of central channel 5. To facilitate
assembly of annular seal 43, bottom member 36 terminates with an annular enlargement
44 for retaining seal 43 on bottom member 36 during assembly.
In the Figure 3 embodiment, annular seal 43 is an O-ring
seal made of elastic polymer material and having a solid oval-shaped cross section.
In the Figure 4 embodiment, annular seal 43 is a lip seal
made of elastic polymer material and having a partly hollow, inverted-U-shaped cross
section. An annular, inverted-U-shaped spring 45 is preferably inserted inside annular
lip seal 43, and may be made of metal or elastomer.
Connector 32 as described above provides for ensuring long-term
sealing, even in the presence of continuous vibration, and is cheap and easy to
produce, by the component parts not requiring particularly accurate machining.