Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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GASEOUS FUEL INJECTOR
Field of the Invention
[0001] The present application relates to a fuel injector for a gaseous
fuel, and more
particularly to a fuel injector that introduces a gaseous fuel directly into a
combustion
chamber of an internal combustion engine.
Background of the Invention
[0002] Gaseous fuels, such as natural gas, have been consumed along with
conventional liquid fuels, such as gasoline, as a fuel for so called bi-fuel,
dual fuel and
other fuel internal combustion engines modified to be fuelled with some
combination of
liquid fuel and gaseous fuel. In this disclosure "bi-fuel" describes engines
that can be
fueled with either one fuel or another fuel, and "dual fuel" describes engines
that are
fueled with two different fuels at the same time. Some engines have also been
made to
be fueled with just a gaseous fuel in so-called "mono-fuel" or "dedicated
natural gas"
engines. However, the base engine that is used as the starting point for
making a gaseous
fuelled engine, no matter which type, has normally been an engine that was
originally
designed and manufactured for liquid fuel, with this base engine requiring
modifications
to operate with a gaseous fuel. This means that the base engine is optimized
for operation
with gasoline or diesel, and gaseous fuels like natural gas are considered a
secondary
fuel. As an example, recent technology improvements for gasoline engines
include the
adoption of direct injection for injecting the gasoline directly into the
combustion
chamber instead of injecting the gasoline somewhere in the intake air system.
Current
product offerings for hi-fuel engines employ direct injection for the gasoline
and port
injection into the intake air ports for the gaseous fuel. Direct injection
provides fuel
economy savings when operating on gasoline, and when operating on CNG such
engines
operate at reduced power due to displacement of oxygen by injecting the
gaseous fuel
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into the intake air system. That is, when gaseous fuel is injected into the
intake air port, a
corresponding volume of air is displaced from entering the combustion chamber,
which
reduces the amount of oxygen available to burn with fuel during each
combustion event,
thereby reducing peak combustion pressure and power output. Due to reduced
power,
these internal combustion engines are typically limited to a narrower range of
engine
operating conditions when operating with natural gas alone, compared to when
it is
fueled with gasoline.
[0003] More recently, there is a growing desire to replace conventional
liquid fuels
with a gaseous fuel as the primary fuel, and even to employ the gaseous fuel
as the only
fuel available to the internal combustion engine in so called mono-fuel or
dedicated CNG
engines. All things being the same, to generate power comparable to a
conventional
liquid-fuelled engine, the gaseous fuel must be introduced after the intake
valve closes so
intake air is not displaced by gaseous fuel. There are fuel injection timing
constraints
when injecting during the compression stroke because as the piston moves
towards the
cylinder head, that is, when it is moving towards top dead center (TDC), the
in-cylinder
pressure increases. When the fuel is pressurized above maximum in-cylinder
compression
pressure it can be introduced generally at any time during the compression
stroke. Liquid
fuels can be pressurized with relative economy and efficiency compared to
gaseous fuels,
since liquid fuels are incompressible fluids compared to gaseous fuels, which
are
compressible. In light duty applications, there are budget constraints that
preclude the
use of gas compressors, which can adjust the pressure of the gaseous fuel as a
function of
engine operating conditions, since the economic and efficiency costs of
pressurizing a
gaseous fuel is considerably more than pressurizing a liquid fuel. In this
circumstance, the
gaseous fuel is compressed beforehand and stored in high pressure storage
tanks, and as
the gaseous fuel is consumed by the engine the pressure of the gaseous fuel in
the storage
tank continues to decrease until the pressure is below a predetermined minimum
pressure
required by the gaseous fuel injector to introduce a predetermined quantity of
fuel within
a predetermined injection window that allows the engine to operate at full
load without
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being derated. Preferably, the predetermined minimum pressure of gaseous fuel
is as low
as possible to increase the useable amount of fuel in the storage tank for
which the engine
can operate at full load. As gaseous fuel is consumed and gaseous fuel
pressure (tank
pressure) decreases, the available injection timing window after the intake
valve closes
also decreases since the gaseous fuel pressure must be greater than in-
cylinder pressure
by a predetermined margin to be able to inject fuel. It is desirable for a
gaseous fuel
injector to be able to introduce the predetermined quantity of fuel within the
predetermined injection window with a reduced gaseous fuel pressure such that
the
useable amount of fuel in the tank increases.
[0004] The energy density of liquid fuels is greater than gaseous fuels.
For a given
volume of liquid fuel, the volume of gaseous fuel that provides an equivalent
amount of
energy is considerably larger. As the pressure of the gaseous fuel decreases,
for example
when the gaseous fuel is consumed by an engine in a system without a gas
compressor to
increase gaseous fuel pressure, the energy equivalent volume of the gaseous
fuel,
compared to the liquid fuel volume, increases. In this circumstance, a gaseous
fuel
injector that injects a gaseous fuel directly into the combustion chamber must
provide a
considerably greater flow area compared to a liquid fuel injector when the
injection
periods for both fuel injectors are the same. Normally the liquid fuel is
pressurized,
which can be accomplished both efficiently and economically, unlike the
gaseous fuel
where in a low cost system is not pressurized due to the greater economic and
efficiency
costs associated with pressurizing a gas. As a result, it is advantageous if
the gaseous fuel
injector injects an energy equivalent amount of fuel at lower minimum
injection pressures
compared to the liquid fuel injector; to accomplish this a higher volumetric
flow rate is
needed for gaseous fuels. Accordingly, gaseous fuel injectors are normally
much larger
than liquid fuel injectors for injecting the same amount of fuel on an energy
basis. When
modifying an engine that was designed for liquid fuel injectors, for example,
in some
engines which have attempted direct injection of gaseous fuels, when replacing
gasoline
direct injectors with CNG direct injectors in the same location, a fuel
injector bore in the
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cylinder head or the cylinder wall is enlarged to accommodate a larger gaseous
fuel
injector. This type of modification to the cylinder head or engine block
increases the cost
of production and changes the thermal behavior of the engine as a result of
the removal of
material that acted as a structural member, which also increases thermal
stress to the
engine, which can reduce engine durability and shorten it's useful lifetime.
[0005] The state of the art is lacking in a gaseous fuel injector that
injects gaseous
fuel directly into a combustion chamber that can supply enough fuel for engine
performance comparable to that of liquid fuel internal combustion engines, and
that can
increase the useable amount of fuel in the storage tank, for an engine fuel
system that
does not pressurize the gaseous fuel above storage pressure.
Summary of the Invention
[0006] An improved fuel injector for injecting gaseous fuel directly into
a
combustion chamber of an internal combustion engine comprises an elongated
nozzle
having a proximal end upstream from a distal end. There is an elongated valve
member
having a first end operatively connected with an actuator and extending
through a
longitudinal bore within the elongated nozzle, and having a second end
opposite the first
end. A valve member guide is disposed within the longitudinal bore between the
elongated nozzle and the elongated valve member for aligning the elongated
valve
member along the longitudinal axis of the elongated nozzle. There is a valve
seat in one
of the distal end of the elongated nozzle and the valve member guide. The
second end of
the valve member cooperates with the valve seat to form a valve. The elongated
valve
member is moveable by the actuator to actuate the valve between a closed
position and an
open position. An outer diameter of a portion of the elongated nozzle in the
combustion
chamber is less than 8 mm, for light duty engines, and 10 mm for medium duty
engines,
and the elongated nozzle, the elongated valve member and the valve member
guide
cooperate to choke the flow area at the valve seat. In a preferred embodiment,
the
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elongated valve member moves into the combustion chamber when the valve is
actuated
from the closed position to the open position.
[0007] The actuator can be one of a solenoid actuator, a solenoid
actuator comprising
a permanent magnet, a piezoelectric actuator and a magnetostrictive actuator.
The
actuator can provide a closing force when the valve is in the closed position.
And when
the fuel injector further comprises a spring that urges the valve closed, the
actuator can
provide at least 80% of the closing force and the spring at most 20% of the
closing force
when the valve is in the closed position. The valve member can be moved
between the
closed position and the open position in less than 700 us, and between the
open position
and the closed position in less than 700 us. The maximum velocity of the valve
member
is between 1 m/s and 1.5 m/s, when the distance between the open position and
the closed
position is at least 400 p.m.
[0008] In a preferred embodiment, a ratio between a diameter of the valve
seat and
the outer diameter of the portion of the elongated nozzle in the combustion
chamber is
between a range of 0.375 (3/8) to 0.625 (5/8). A flow area upstream from the
valve seat is
at least 1.5 times, and preferably at least 2 times, the flow area at the
valve seat. A
distance between the open position and the closed position is at least 400 um,
and
preferably in a range of 400 um and 600 p.m. An outer diameter of the valve
member in
the elongated nozzle is at most 2.5 mm and an inner diameter of the elongated
nozzle is at
least 4 mm. An outer diameter of a portion of the elongated nozzle in a bore
in one of a
cylinder head and a cylinder wall of the internal combustion engine is less
than 8 mm.
The outer diameter of the portion of the elongated nozzle in the combustion
chamber is
between a range of 7.5 mm and 7.7 mm.
[0009] The gaseous fuel is introduced into the combustion chamber at an
injection
pressure of at most 30 bar, and with an injection timing after an intake valve
associated
with the combustion chamber closes and before 90 TDC. In a preferred
embodiment, the
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gaseous fuel is natural gas and the gaseous fuel injector provides a mass flow
of 16 g/s of
natural gas into the combustion chamber when the valve is in the open
position.
[0010] In a preferred embodiment, the elongated nozzle further comprises
an inner
shelf, and the valve member guide further comprises a sleeve extending along
the
longitudinal axis of the gaseous fuel injector; and an annular collar extends
around the
sleeve. The annular collar abuts the inner shelf in the elongated nozzle and
is secured
thereto. The valve member guide further comprises two or more elongated
protrusions
extending radially outwardly from the sleeve and abutting an inner surface of
the
elongated nozzle.
[0011] In another preferred embodiment, the valve member guide comprises at
least
two semi-annular segments extending around different portions of an outer
circumference
of the valve member and spaced apart from each other along the longitudinal
axis of the
fuel injector. The different portions of the outer circumference can be
partially
overlapping. The at least two semi-annular segments can be connected to the
valve
member, or alternatively to the nozzle.
[0012] In yet another preferred embodiment, the valve guide is a valve
guide and seat
member comprising an annular portion having a valve seat and a conical section
on an
inner radial surface; a sleeve spaced apart from the annular portion; and at
least two
elongate protrusions extending from the sleeve towards an inner surface of the
elongated
nozzle and to the annular portion. The valve member is guided by the sleeve.
In preferred
embodiments, the valve member can comprise a needle and an annular abutment
member
extending around the needle and secured thereto, and spaced apart from the
valve guide
and seat member. When the actuator is activated to move the valve member to
the open
position, the valve member is stopped when the abutment member abuts the valve
guide
and seat member.
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[0013] In still another preferred embodiment, the valve member comprises a
needle
and a spring retainer secured thereto, and the elongated nozzle further
comprises a spring
and a retaining and abutment member comprising an annular disc; an elongated
cylindrical portion extending from the disc; and an annular protrusion
extending radially
outwards from the elongated cylindrical portion at an end opposite the annular
disc. The
spring is retained between the spring retainer and the annular disc, and the
annular
protrusion operates as a positive stop for the spring retainer when the valve
member is
made to move by the actuator. A compression spring extending between the
elongated
nozzle and the spring retainer urges the valve to the closed position. A fuel
injector body
has opposing ends and defines an interior space. One end of the fuel injector
body is
connected with an end of the elongated nozzle opposite the valve seat. In a
preferred
embodiment, the fuel injector body is a metallic tube.
[0014] The actuator can comprise a lower flux guide within the fuel
injector body; an
upper flux guide within the fuel injector body spaced apart from the lower
flux guide
along the longitudinal axis, and an armature secured to the valve member and
moveable
between the lower and upper flux guides. The valve member can extend through
the
lower and upper flux guides and the armature. The lower and upper flux guides
and the
armature each comprise passageways dimensioned to provide a flow area at least
1.5
times the flow area at the valve seat. An upper valve member guide, in the
form of a
sleeve, is received in a bore in the lower flux guide, and guides the valve
member. A
preload spring extends into the upper flux guide and biases the valve member
open. One
end of the preload spring abuts the armature. A preload adjuster is secured
with the fuel
injector body and abuts an end opposite the one end of the preload spring to
adjust the
tension thereof.
[0015] An annular retainer is connected with an end of the fuel injector
body opposite
the elongated nozzle. A gaseous fuel fitting is connected with an end of the
annular
retainer opposite the fuel injector body. A fluid communication channel
extends from the
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gaseous fuel fitting through the annular retainer, the fuel injector body and
the elongated
nozzle to the valve. The annular retainer comprises a first annular portion
connected to
the body, and a second annular portion threadedly received in the first
annular portion
and threadedly receiving the preload adjuster and the gaseous fuel fitting.
[0016] An improved fuel injector for injecting gaseous fuel directly into
a combustion
chamber of an internal combustion engine comprises an elongated nozzle having
a
proximal end upstream from a distal end. There is an elongated valve member
having a
first end operatively connected with an actuator and extending through a
longitudinal
bore within the elongated nozzle, and having a second end opposite the first
end. A valve
member guide is disposed within the longitudinal bore between the elongated
nozzle and
the elongated valve member for aligning the elongated valve member along the
longitudinal axis of the elongated nozzle. There is a valve seat in one of the
distal end of
the elongated nozzle and the valve member guide. The second end of the valve
member
cooperates with the valve seat to form a valve. The elongated valve member is
moveable
by the actuator to actuate the valve between a closed position and an open
position. There
is a compression spring urging the valve to the closed position. When the
valve is in the
closed position, both the actuator and the compression provide a closing
force.
[0017] An improved fuel injector for injecting gaseous fuel directly into
a combustion
chamber of an internal combustion engine comprises an elongated nozzle having
a
proximal end upstream from a distal end. There is an elongated valve member
having a
first end operatively connected with an actuator and extending through a
longitudinal
bore within the elongated nozzle, and having a second end opposite the first
end. A valve
member guide is disposed within the longitudinal bore between the elongated
nozzle and
the elongated valve member for aligning the elongated valve member along the
longitudinal axis of the elongated nozzle. There is a valve seat in one of the
distal end of
the elongated nozzle and the valve member guide. The second end of the valve
member
cooperates with the valve seat to form a valve. The elongated valve member is
moveable
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by the actuator to actuate the valve between a closed position and an open
position. The
displacement of the elongated valve member between the closed position and the
open
position is at least 400 p.m.
[0018] An improved fuel injector for injecting gaseous fuel directly into
a combustion
chamber of an internal combustion engine comprises an elongated nozzle having
a
proximal end upstream from a distal end. There is an elongated valve member
having a
first end operatively connected with an actuator and extending through a
longitudinal
bore within the elongated nozzle, and having a second end opposite the first
end. A valve
member guide is disposed within the longitudinal bore between the elongated
nozzle and
the elongated valve member for aligning the elongated valve member along the
longitudinal axis of the elongated nozzle. There is a valve seat in one of the
distal end of
the elongated nozzle and the valve member guide. The second end of the valve
member
cooperates with the valve seat to form a valve. The elongated valve member is
moveable
by the actuator to actuate the valve between a closed position and an open
position. The
actuator moves the elongated valve member between the closed position and the
open
position in at most 700 [is, and the actuator moves the elongated valve member
between
the open position and the closed position in at most 700 ps.
Brief Description of the Drawings
[0019] FIG. 1 is a cross-sectional view of a gaseous fuel injector
according to a first
embodiment.
[0020] FIG. 2 is a cross-sectional view of a nozzle of the gaseous fuel
injector of FIG.
1.
[0021] FIG. 3 is cross-sectional view of a valve member of the gaseous
fuel injector
of FIG. 1.
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[0022] FIG. 4 is a perspective view of a valve member guide of the gaseous
fuel
injector of FIG. 1 according to a first embodiment.
[0023] FIG. 5 is a cross-sectional view of a sleeve of the valve member
guide of FIG.
4.
[0024] FIG. 6 is a perspective view of a collar of the valve member guide
of FIG. 4.
[0025] FIG. 7 is a perspective view of a lower flux guide of an actuator
assembly of
the gaseous fuel injector of FIG. 1.
[0026] FIG. 8 is a perspective view of an upper flux guide of an actuator
assembly of
the gaseous fuel injector of FIG. 1.
[0027] FIG. 9 is a perspective view of an armature of an actuator assembly of
the
gaseous fuel injector of FIG. 1.
[0028] FIG. 10 is a partial cross-sectional view of a nozzle assembly for
the gaseous
fuel injector of FIG. 1 according to a second embodiment.
[0029] FIG. 11 is a partial perspective view of an assembly of a valve member
guide
and a valve member of the nozzle assembly of FIG. 10.
[0030] FIG. 12 is a partial cross-sectional view of a nozzle assembly
comprising a
valve member guide for the gaseous fuel injector of FIG. 1 according to a
third
embodiment.
[0031] FIG. 13 is a perspective view of a valve guide and seat member of
the nozzle
assembly of FIG. 12.
[0032] FIG. 14 is a cross-sectional view of the valve guide and seat member
of FIG.
13.
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[0033] FIG. 15 is a perspective view of an abutment member of the nozzle
assembly
of FIG. 12.
[0034] FIG. 16 is a partial, cross-sectional view of a nozzle assembly
for the gaseous
fuel injector of FIG. 1 according to a fourth embodiment.
Detailed Description of Preferred Embodiment(s)
[0035] Referring to FIGS. 1 through 6, there is shown fuel injector 100
according to
one embodiment that injects gaseous fuel directly into a combustion chamber of
an
internal combustion engine. A gaseous fuel is any fuel that is in a gas state
at standard
temperature and pressure, which in the context of this application is 20
degrees Celsius
("C) and 1 atmosphere (atm). By way of example, typical gaseous fuels include,
without
limitation, natural gas, propane, hydrogen, methane, butane, ethane, other
known fuels
with similar energy content, and mixtures including at least one of these
fuels. Natural
gas itself is a mixture, and it is a popular gaseous fuel for internal
combustion engines
because it is abundant, less expensive and cleaner burning than oil-based
liquid fuels, and
the sources are broadly dispersed geographically around the world. Fuel
injector 100
comprises nozzle assembly 110, actuator assembly 120 and fuel inlet assembly
130. Each
of the assemblies comprises a collection of components that cooperate to
provide
functionality intended by the respective assembly, as will become apparent in
the course
of this application. Certain components span one or more assemblies and when
describing
these sections these components will at least be described with respect to the
purpose the
component serves in the respective assembly.
[0036] Nozzle assembly 110 comprises nozzle 140, shown in FIG. 2, which is
hollow
and open ended in construction, having valve seat 150 at distal end 160,
interior shelf 170
near proximal end 180, and interior space 190 therebetween. Fuel injector 100
is installed
in a bore, for example in a cylinder head or cylinder wall in an engine block,
such that
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portion 200 of nozzle 140 resides inside a combustion chamber. Annular groove
210
receives a seal (not shown), such as a polymer ring or the like, that seals
nozzle 140
against the bore in the cylinder head or the engine block, depending upon
where the fuel
injector is installed. Elongated valve member 220, shown in FIG. 3, comprises
needle 222
that extends into the opening at distal end 160 of the nozzle and through
interior space
190 into actuator assembly 120, and head 224 that in cooperation with valve
seat 150
forms injection valve 230. In the illustrated embodiment fuel injector 100 is
an outwardly
opening fuel injector, meaning injection valve 230 opens when head 224 of the
elongated
valve member moves away from contact with valve seat 150, and remains open so
long
as head 224 is spaced from valve seat 150. Nozzle valve member guide 240,
shown in
FIG. 4, is rigidly connected with nozzle 140 by annular collar 310, which is
fixedly
attached, for example, by welding, to outer surface 320 of sleeve 250 and to
nozzle 140
where it abuts shelf 170. In assembled fuel injector 100, installed needle 222
extends
through hollow sleeve 250, which guides the movement of needle 222 along
longitudinal
axis 260 so that head 224 remains aligned with valve seat 150 to improve
sealing and for
more consistently distributed fluid flow through nozzle 110, when needle 222
is actuated
by actuator assembly 120, as will be discussed in more detail below. In the
embodiment
shown in FIG. 4, elongated protrusions 280 extend radially outwardly from
sleeve 250
and abut inner surface 290 of nozzle 140 and serve to align end 300 of valve
member
guide 240 with longitudinal axis 260. Valve bias means 330 comprises spring
retainer
340, which is fixedly attached, for example by a welded connection, to valve
member
220, and helical compression spring 350 retained between proximal end 180 of
nozzle
140 and the retainer, which urges head 224 towards valve seat 150 such that
valve 230 is
biased to the closed position. The location of spring retainer 340 along valve
member 220
is selected in combination with the spring constant and other characteristics
of helical
compression spring 350 to provide a predetermined biased closing force for
valve 230.
Annular protrusion 270 of valve member guide 240 extends radially outwardly
from
sleeve 250, and serves to act as a positive stop (an abutment) to constrain
movement of
valve member 220. That is, with respect to the illustrated embodiment, when
actuator
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assembly 120 activates valve 230 to open, the distance that valve member 220
can travel
is limited by spring retainer 340 coming into contact with annular protrusion
270. In the
shown embodiment fuel injector body 360 is in the form of a thin-walled
metallic tube,
with an L-shaped end that abuts annular shelf 370 on nozzle 140. Injector body
360 is
removably attached to nozzle 140, by locknut 380 which engages nozzle 140 by
means of
threaded assembly 375, but in other embodiments it can be welded to nozzle
140. Injector
body 360 extends from nozzle assembly 110, through actuator assembly 120, to
fuel inlet
assembly 130. Annular seal 390 extends around longitudinal axis 260 of nozzle
140 and
fluidly seals the nozzle with fuel injector body 360.
10037] When the base engine is a gasoline-fueled direct injection light
duty engine, a
gaseous fuel injector with the features described herein is enabled to be
manufactured
with the outer diameters of portions 200 and 205 of nozzle 140 being less than
8
millimeters (mm), and preferably between 7.5 mm and 7.7 mm, such that gaseous
fuel
injector 100 can be installed into standard sized fuel injector bores employed
for gasoline
direct injectors. When gaseous fuel injector 100 is to be installed into a
standard sized
fuel injector bore in a medium duty engine, the described features enable the
outer
diameters of portions 200 and 205 to be less than 10 mm. In this application
light duty
engines are defined to be engines that have swept volumes of less than 900
cubic
centimeters (cc) per cylinder, and that typically have cylinder bore diameters
less than
105 mm, and medium duty engines are defined to be engines that have swept
volumes
between 900 cc and 1700 cc per cylinder, and that typically have cylinder bore
diameters
between 105 mm and 140 mm. By installing gaseous fuel injector 100 into
standard sized
fuel injector bores, the conversion of an engine that employs gasoline direct
injectors to
one that employs natural gas direct injectors, such as gaseous fuel injector
100, is
simplified. The cooperation of the components in nozzle assembly 110, where
the outer
diameter is reduced compared to that of actuator assembly 120 and fuel inlet
assembly
130, provides a fuel flow area (described in more detail below) that enables
direct
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replacement of gasoline direct injectors without requiring modification to
fuel injector
bores.
[0038] With reference to FIG. 1, actuator assembly 120 is now described
in more
detail. In the illustrated and preferred embodiment, actuator 400 is a
solenoid-type
actuator that employs at least one permanent magnet and has a constant overall
air gap
length in the flux paths of the actuator to generate a force that acts on an
armature
connected to valve member 220. In other embodiments solenoid actuators that do
not
comprise a permanent magnet and/or have a constant overall air gap length can
be
employed, as well as strain-type actuators such as piezoelectric actuators and
magnetostrictive actuators. Actuator 400 is spaced apart, along the
longitudinal axis, from
nozzle assembly 110. Annular support 410 abuts annular shelf 420 (seen in FIG.
2)
around nozzle 140 and extends away from proximal end 180 inside fuel injector
body 360
and supports annular spacer 430. Components of actuator 400 inside fuel
injector body
360 are supported by spacer 430. Lower flux guide 440, in the form of an
annulus in the
illustrated embodiment, abuts annular spacer 430 and is radially and axially
constrained,
with respect to longitudinal axis 260, by fuel injector body 360. The lower
flux guide
provides a path for magnetic flux associated with actuator 400. In this
application the
term lower refers to items further downstream, with respect to fuel flow, in
fuel injector
100, and the term upper refers to items further upstream, where fuel flows
into fuel inlet
assembly 130 and out of nozzle assembly 110. Actuator valve member guide 450
extends
into a bore of lower flux guide 440 and serves to align the axial movement of
valve
member 220 through the lower flux guide in actuator assembly 120. Upper flux
guide
470, in the form of an annulus in the illustrated embodiment, is spaced apart
from lower
flux guide 440, and is radially and axially constrained, with respect to
longitudinal axis
260, by fuel injector body 360. Armature 480, also in the form of an annulus
in the
illustrated embodiment, is positioned between lower and upper flux guides 440
and 470
respectively, and is fixedly attached to valve member 220, for example by a
weld, such
that air gap 490 is a predetermined distance. When actuator 400 is activated
it operates to
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move armature 480 and valve member 220, such that valve 230 either opens or
closes
depending on the direction of movement of the valve member. Lower and upper
flux
guides 440 and 470 have passageways 620 and 630 respectively, and armature 480
has
passageways 640, seen in FIGS.7, 8 and 9 respectively, that are dimensioned to
provide a
predetermined flow area for gaseous fuel therethrough, which is at least 1.5
times the
flow area through valve 230 when opened. In the illustrated embodiment, the
passageways 620, 630 and 640 are in the form of slots. The slots forming
passageways
620 in flux guide 440 of FIG. 7 extend radially from the bore of the annulus
and from end
to end of the flux guide, and for a portion of the longitudinal extent to the
outer radial
surface of the flux guide. In addition to fuel passage, the passageways also
reduce eddy
current losses that result when actuator 400 is activated causing a varying
magnetic field
in the lower and upper flux guides and the armature.
[0039] Referring again to FIG. 1, annular flux guides 500 and 510, also
called stator
segments, extend around the outer surface of fuel injector body 360 and form
magnetic
flux paths with lower flux guide 440 and upper flux guide 470 respectively.
Permanent
magnet 520 extends annularly around fuel injector body 360 and forms a
magnetic flux
path with armature 480 and flux guides 510 and 530. Flux guide 530 extends
annularly
around the permanent magnet and forms additional magnetic flux paths with flux
guides
500 and 510. Stator housing 540 retains flux guides 500, 510, 530 and
permanent magnet
520 to fuel injector body 360, and is fixedly attached thereto, such as by a
weld. Coil 570
extends annularly around the outer surface of fuel injector body 360 and is
electrically
connected with an electrical connection (not shown), which in turn is
electrically
connected with an actuator driver (not shown) for activating actuator 400 to
open and
close valve 230. Actuator assembly 120 further comprises preload spring 550
extending
into a bore of upper flux guide 470 and abutting armature 480. By positioning
preload
spring 550 in this way, the overall length of fuel injector 100 along
longitudinal axis 260
is reduced. Positional adjustment of inner preload adjuster 560, to set the
tension of
preload spring 550 on armature 480, is allowed by a threaded connection with
retainer
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600, which is described in more detail when discussing fuel inlet assembly 130
below.
Generally, preload spring 550 is at least loaded by an amount that when valve
230 is fully
opened the preload spring does not reach its free length (fully extended). A
shim can be
employed between preload spring 550 and armature 480, depending upon the
material of
the armature, to avoid fretting.
[00401 When valve 230 is closed, there is an opening force acting on the
valve from
preload spring 550 and fuel pressure within fuel injector 100, which is
balanced by a
closing force provided by permanent magnet 520 and spring 350. Magnetic flux
from
permanent magnet 520 flows through armature 480, upper flux guide 470 and flux
guides
510 and 530, thereby latching the armature to the upper flux guide when the
valve is
closed. In other embodiments that do not employ an actuator comprising a
permanent
magnet, the actuator can be activated to apply a portion of the closing force
when valve
230 is closed, for example by energizing an electromagnet of a solenoid
actuator.
Alternatively, or additionally, actuator 400 can provide the closing force
using other
known techniques. In a preferred embodiment, permanent magnet 520 provides
approximately 90% of the closing force when head 224 of valve member 220 is
seated on
valve seat 150, and spring 350 provides approximately 10% of the closing
force. In this
circumstance, when valve 230 is opened, spring 350 compresses, and the closing
force
provided by the spring increases according to the spring rate. When the valve
is biased in
this manner, spring 350 and permanent magnet 520 can both be made smaller,
thereby
reducing the size of fuel injector 100 in the corresponding regions where
these
components are located. In other preferred embodiments, spring 350 can provide
up to
20% of the closing force and permanent magnet 520 can provide at least 80% of
the
closing force, when head 224 is seated on valve seat 150.
[0041] In a preferred embodiment actuator 400 moves head 224 of valve member
220
from the closed position, in fluidly sealed contact with valve seat 150, to
the open
position a distance of at least 400 micrometers (pm) away from the closed
position, and
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preferably between 400 pm and 600 pm. By moving head 224 at least 400 pm the
flow
area through valve 230 is increased, compared to previously known gaseous fuel
injectors
that move valve members no more than 300 pm, which increases the rate at which
gaseous fuel is introduced into the combustion chamber, thereby allowing a
predetermined quantity of gaseous fuel to be introduced at a lower gaseous
fuel pressure,
compared to previous gaseous fuel injectors employing an equivalent injection
window,
which increases the useable fuel in a gaseous fuel storage tank, and
accommodates
decreasing the outer diameters of portions 200 and 205 of nozzle 140 to and
below 8 mm
for light duty engines, and below 10 mm for medium duty engines, without
sacrificing
engine performance. Actuator 400 in cooperation with valve member 220, valve
member
guide 140 and spring 350, opens valve 230 from the closed position to the open
position
in less than 700 microseconds (ps), and similarly closes the valve from the
open position
to the closed position in less than 700 ps. In a preferred embodiment, the
opening and
closing time for valve 230 is less than 500 ps. The maximum velocity of valve
member
220 is between 1 meters/second (m/s) and 1.5 m/s during flight, either opening
or closing,
and when the valve member nears the end of its stroke, actuator 400 can be
activated with
debounce or parachute pulses to decelerate the valve member before impact.
[0042] With reference to FIG. 1, fuel inlet assembly 130 is described in
more detail.
Annular retainer 590 is fixedly attached to fuel injector body 360, for
example by
welding, and removably joined to spigot retainer 600, for example, by a
threaded
connection as shown. Annular seals 605 and 606 fluidly seal inlet assembly
130. The
threaded connections allow greater serviceability of fuel injector 100 because
it allows
easier access for repair and replacement of internal components, or modular
servicing that
permits the retention of the fuel inlet assembly and replacement of just the
internal
components of the actuator assembly or just the internal components of the
nozzle
assembly. However, in other embodiments retainers 590 and 600 can be rigidly
connected such as by a weld, or can be manufactured as a unitary component.
The
threaded connection between preload adjuster 560 and retainer 600 allows the
force
CA 02857396 2014-07-18
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applied to valve member 220 by preload spring 550 to be adjusted by screwing
the
preload adjuster toward or away from the valve member, which compresses and
decompresses the preload spring respectively. In other embodiments preload
adjuster 560
can be replaced by a preload spring spacer, which can be fixed into position
relative to
retainer 600 to permanently set the preload force. Gas fitting 610 fluidly
connects with a
source of gaseous fuel, such as a fuel rail (not shown). In alternative
embodiments, gas
fitting 610 can be fixedly attached to retainer 600, for example by welding,
or formed as
a unitary component, with preload adjuster 560 inserted and threaded into the
retainer
portion from the lower side.
[0043] The fluid passages through which the gaseous fuel flows from gas
fitting 610
to valve seat 150 are designed to increase volumetric flow capacity compared
to
previously known designs by a unique combination of known techniques and novel
features. For example, in the actuator assembly, as shown in FIGS. 7 to 9,
slotted
openings 620, 630 and 640 are provided in respective lower flux guide 440,
upper flux
guide 470 and armature 480 to increase the flow area through such components.
Gaseous
fuel flows out of actuator 400 through annular spacer 430, around spring
retainer 340 and
spring 350, and through openings 650 and 655 formed between collar 310 and
sleeve 250
(seen in FIG. 4). Within nozzle 140, gaseous fuel flows between sleeve 250 and
inner
surface 290 of the nozzle, around elongated protrusions 280 and through valve
230, when
opened.
[0044] The flow area through fuel injector 100 is choked at valve 230, and
when the
valve is in the open position, the flow area through the valve is at least 4.5
mm2, and
preferably 5 min2. In portion 200 of nozzle 140, the inner diameter of the
nozzle is at
least 4.2 mm and the outer diameter of needle 222 is at most 2.4mm, and
preferably
2.2mm, thereby defining a flow area of around 10 min2. In portion 205 of
nozzle 140, the
inner diameter of nozzle 140 is at least 6 mm, and the outer diameter of
sleeve 230 in this
region is at most 3.6 mm, except around elongate protrusions 280 which extend
to inner
CA 02857396 2014-07-18
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surface 290 of the nozzle, thereby defining a flow area at most of around 18
mm2. The
inner diameter of nozzle 140 is reduced in portion 200, compared to portion
205, as a
consequence of annular groove 210, which is required for retaining a sealing
member that
seals the combustion chamber, and as a result the outer diameter of needle 222
is
constrained such that a predetermined flow area is maintained in this region.
Nozzle 140,
valve member 220 and valve member guide 240 cooperate to provide a flow area
that is
at least 1.5 times the flow area through valve 230 when opened, and preferably
at least
between 2 and 3 times the flow area. Since the respective outer diameters of
actuator
assembly 120 and fuel inlet assembly 130 are much larger than nozzle assembly
110, for
example around 25 mm, the challenge of achieving a flow area of at least 1.5
times that
through valve 230 is reduced compared to the nozzle assembly. By choking the
flow at
valve seat 150, and providing an upstream flow area to valve seat flow area
ratio of
between 1.5 and 3, the pressure drop between the gaseous fuel rail (not shown)
and valve
seat 150 is reduced and preferably minimized, which improves the mass flow
rate of the
fuel injection spray cone into the combustion chamber, for an outwardly
opening injector,
and the mass flow rates of fuel jets, for an inwardly opening injector. For
light duty
engines, when valve 230 is opened fuel injector 100 can provide a fuel flow
rate of 16
grams/second (g/s) of natural gas, for example, when natural gas pressure is
30 bar and
injection timing is before 90 before TDC during the compression stroke, and
for medium
duty engines the fuel injector can provide a flow rate of 30 g/s under similar
constraints.
When natural gas pressure is 15 bar, fuel injector 100 can provide a fuel flow
rate of 8 g/s
for a light duty engine, and 15 g/s for a medium duty engine.
[0045] When valve 230 is closed, the opening force provided by fuel
pressure inside
fuel injector 100 and preload spring 550, which acts on head 224, increases as
the size of
the valve seat diameter Ds (seen in FIG. 2) increases. In preferred
embodiments, to hold
valve 230 in a closed position, actuator 400, or a combination of the actuator
and spring
350, provides a closing force greater than the opening force. As diameter Dvs
increases
typically actuator 400, or spring 350, or both, increase in size. It is
desirable for the
CA 02857396 2014-07-18
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overall outer diameter of fuel injector 100 be less than 30mm, such that
installation into a
variety of engines can be accommodated. The outer diameter of fuel injector
100 can be
constrained to less than 30 mm when a ratio between the valve seat diameter
Dvs and the
diameter DN,200 of portion 200 of the nozzle (seen in FIG. 2) in the
combustion chamber
is between a range of 0.375 (3/8) to 0.625 (5/8). In addition to constraining
the overall
outer diameter of fuel injector 100, it is desirable to maintain a minimal
wall thickness of
portion 200 of the nozzle, in the combustion chamber, where combustion forces
acting on
the nozzle may cause reduced lifetime of the fuel injector when the wall
thickness in this
region becomes too thin. When the Dvs to DN,200 ratio is between 0.375 and
0.625, and
when the diameter of portion 200 is between 7 and 10 mm, the wall thickness of
portion
200 of the nozzle has a desirable margin of safety for durability.
[0046] Referring now to FIGS. 10 and 11, nozzle assembly 112 is a second
embodiment that comprises valve member guide 242 instead of a sleeve-style,
like valve
member guide 240 shown in FIG. 4. Stepped and staggered semi-annular guide
segments
282a, 282b and 282c (282a-c) each extend around a portion of the outer
circumference of
needle 222, such that the flow area around each segment is at least 1.5 times
the flow area
at the valve seat when valve 231 is open. Semi-annular guide segments 282a-c
are each
located at a different axial location along longitudinal axis 260 (stepped),
and each
supports needle 222 at a different circumferential location around the needle
(staggered),
however the guide segments can be overlapping around the circumference. In the
illustrated embodiment guide segments 282a-c resemble a staircase. In other
embodiments, at least two semi-annular guide segments are employed to guide
valve
member 220. Semi-annular guide segments 282a-c can be connected with needle
222, or
can be connected to an inner surface of nozzle 141; the former technique
simplifies
manufacturing of the nozzle and the latter technique decreases needle mass.
[0047] Referring now to FIGS. 12, 13, 14 and 15, nozzle assembly 113 is
shown
according to a third embodiment. Valve guide and seat member 660 comprises
annular
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portion 670 having valve seat 150 on an inner surface of the annulus, sleeve
253 spaced
apart from the annular portion, and elongated protrusions 283 that extend from
sleeve 253
to the annular portion and to the inner surface of portion 200 of nozzle 143
to assist with
centering of sleeve 253 during assembly. Needle 222 (seen in FIG. 12) extends
through
and is guided by sleeve 253. In the illustrated embodiment there are four
protrusions 283,
preferably equally spaced around longitudinal axis 260. In other embodiments
there can
be at least two elongated protrusions, and possibly more than four, providing
the flow
area past elongated protrusions 283 in the nozzle is at least 1.5 times the
flow area
through valve 230 when in the open position. Edge 675 is at the intersection
of two
transverse surfaces in the illustrated embodiment. In other preferred
embodiments edge
675 can be replaced by a conical surface, or a chamfered or rounded corner to
improve
the flow of gaseous fuel through annular portion 670 by reducing turbulence as
the fuel
flows past protrusions 283 towards valve 230. In the illustrated embodiment,
the lower
end of nozzle 143 receives valve guide and seat member 660 such that annular
portion
670 abuts with nozzle 143 and is fixed thereto, such as by welding. Retaining
and
abutment member 700 abuts shelf 170 and comprises disc portion 710 extending
from
bore 720 radially outwardly towards inner surface 730 of nozzle 143.
Protrusions 715
extend radially outwardly from disc portion 710 to inner surface 730 of the
nozzle and
axially below disc portion 710 such that passageways 760 for fuel are formed
between
member 700 and nozzle 143. Compression spring 350 (shown in FIG. 1) is
retained
between disc portion 710 and spring retainer 340 (shown in FIG. 1). Elongated
cylindrical portion 690 extends from disc portion 710 and annular protrusion
273 extends
radially outwardly from cylindrical portion 690, and serves to act as a
positive stop (an
abutment) to constrain movement of valve member 220. In this embodiment,
cylindrical
portion 690 does not act as a guide for needle 222. While guidance for needle
222 is not
needed in the illustrated embodiment, in other embodiments it could, for
example for
configurations that have a longer and/or thinner needle. When actuator
assembly 120
(shown in FIG. 1) activates valve 230 to open, the distance valve member 220
can travel
is limited by spring retainer 340 abutting annular protrusion 273.
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[0048] Referring now to FIG. 16, nozzle assembly 114 is shown according to a
fourth
embodiment. Annular abutment member 701 extends around needle 222 of the valve
member and is fixedly attached thereto. Coil spring 350 (shown in FIG. 1) is
retained
between spring retainer 340 (shown FIG. 1) and shelf 170 of nozzle 144. When
actuator
assembly 120 (shown in FIG. 1) is activated to move valve member 220 such that
valve
230 opens, the travel of the valve member is stopped when abutment member 701
abuts
valve guide and seat member 660. Fuel flows around an outer periphery of
abutment
member 701 between the inner surface of nozzle 144 and the outer periphery.
Compared
to the embodiment of FIGS. 12 to 15, this embodiment simplifies the nozzle
assembly by
replacing retaining and abutment member 700 with abutment member 701, which is
less
complicated to manufacture. However, this embodiment increases the moving mass
of the
valve member which can delay opening and closing times.
[0049] While particular elements, embodiments and applications of the
present
invention have been shown and described, it will be understood, that the
invention is not
limited thereto since modifications can be made by those skilled in the art
without
departing from the scope of the present disclosure, particularly in light of
the foregoing
teachings. By way of example, it will be understood by persons familiar with
injector
technology that certain variations, such as integration of components like the
integration
of sleeve 250 with one or more of annular protrusion 270, annular collar 310
and/or
elongated protrusions 280 by casting, to obviate welded joints, can be
employed without
departing from the spirit of the disclosed invention as claimed.
