Note: Descriptions are shown in the official language in which they were submitted.
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FUEL INJECTI~N VALVE
Field of the Invention
[0001] 'fhe present invention relates to a fuel injection valve and a
method of operating such a fuel injection valve for controlling fuel flow
into an internal combustion engine. More particularly, the fuel injection
valve comprises a nozzle arrangement that provides a substantially
constant flow rate for a predetermined range of valve needle movement.
background of the Invention
[0002] A fuel injection valve can employ a number of control
strategies for governing the quantity of fuel that is introduced into the
10 combustion chamber of an internal combustion engine. For example,
some of the parameters that can be manipulated by commonly known
control strategies are the pulse width ofthe injection event, fuel pressure,
and the valve needle lift.
(0003] The "pulse width" of an injection event is defined herein by
the time that a fuel injection valve is open to allow fuel to be injected into
the combustion Chamber. Assuming a constant fuel pressure and a
constant valve needle lift, a longer pulse width l;enerally results in a
larger
quantity of fuel being introduced into the combustion chamber.
[0004] 1=Iowever, fuel pressure need not be constant from one
injection event to another and fuel pressure can be raised to increase the
quantity of fuel that is introduced into the combustion chamber.
Conversely fuel pressure can be reduced to injecr~ a smaller quantity of fuel
into the engine, for example during idle or low load conditions.
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[0005] As yet another example, some t3~pes of fuel injection valves
can control valve needle lift to influence the quantity of fuel that is
introduced into a corr.~bustion chamber. An increase ire needle lift
generally corresponds to an increase in the quantity of fuel that is injected
and some fuel injection valves can be controlled to hold the valve needle
at an intermediate position between the closed and fully open positions to
allow a flow rate that is less than a maximum flow rate. To control valve
needle lift a fuel injection valve can employ mechanical devices or an
actuator that is controllable to Iift a~xd hold the needle at intermediate
positions between the closed and fully open positions.
[0006] A difficult task for known control strategies is controlling
the quantity of fuel that is injected into an engine's combustion chamber
under idle or low load conditions. Under such conditions the fuel injection
valve is required to inject only a small amount of fuel into the combustion
chamber, and even small variations in the quantity of fuel that is injected
into the combustion chamber can result in a significant variance in the
injected quantity of fi~.el that can cause unstable operation. Under high
load conditions, variations in the quantity of fuel of the same order of
magnitude have Iess impact on engine operation because they represent a
much smaller variation in the difference between the desired quantity of
injected fuel versus the actual quantity of injected fuel, when this
difference is considered as a percentage of the total quantity of injected
fuel.
[0007] 'fo control the quantity of fuel injected during idle and low
load conditions, if the control strategy manipulates only pulse width, this
strategy can result in a pulse width that is too short to provide consistent
and efficient combustion. Accordingly, simply shortening pulse width at
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idle or low load conditions to reduce the quantity of injected fuel is not a
desirable strategy.
[0008] A pulse width sufficiently long for idle or low load
conditions can be achieved by reducing the fuel pressure. For liquid fuels
this is a viable strategy, but it requires a system for controlling fuel
pressure, adding to the cost and complexity of the fuel injection system.
For example, known liquid fuel systems can reduce fuel pressure by
returning a portion of the high-pressure fuel to i:he fuel tank. With liquid
fuels, there are limitations on how low the pressure can be reduced since a
minimum fuel pressure is required to atomize the fuel when it is
introduced into the engine's combustion chamber. However, this
approach is more difficult with a gaseous fuel. Since a gas is a
compressible fluid, compared to a liquid fuel, much more gaseous fuel
must be returned to the fuel tank fox a comparable reduction in fuel
pressure, and if the gaseous fuel tank is pressurized, there can be times
when the tank pressure exceeds the fuel rail pressure, making return flow
impossible. Furthermore, it can be difficult to control fuel pressure to
achieve the desired responsiveness for controlling the fuel injection mass
flow rate during an injection event or from one injection event to the next.
It can also be difficult to control fuel pressure and injection valve
operation to accurately inject the exact quantity of fuel with the precision
desired for each injection event, and again, only small variations in fuel
quantity can cause unstable operating conditions.
[0009] If a fuel injection valve is operable to control valve needle
lift, flow rate can be controlled to provide a suflieiently long pulse width
to inject the desired quantity of fuel for an engine that is idling or
operating under low load conditions. As shown. by Tapanese Patent
Application No. 60031204 a fuel infection valve can be provided with a
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stopper that is movable to limit the lift of the valve needle. This type of
mechanical arrangement adds considerable complexity to the fuel injection
valve and, consequently, higher manufacturing costs, space requirements
for installing the injection valve assembly, maintenance costs, and
5 reliability concerns.
[0010] In another approach, fuel injection valves are known that
control the quantity of injected fuel by employing variable orifice areas.
That is, the injection valve can have two sets of orifices whereby the valve
is operable to inject fuel through only one set of orifices when a smaller
10 quantity of fuel is to be injected, and fuel is injected through both sets
of
orifices when a larger quantity of fuel is to be injected. United States
Patent
No. 4,546,739 discloses an example of such an injection valve.
Like other known mechanical solutions this arrangement adds complexity
and the associated disadvantages of higher manufacturing costs,
15 maintenance costs, and concerns for reliability.
[0011] Another type of fuel injection valve can be directly actuated
by a strain-type actuator, which can be commanded to lift the valve needle
to any position between its closed and open position. Co-owned United
States Patent Nos. 6,298,829, 6,564,777, 6,575,138 and 6,584,958, disclose
20 examples of directly actuated fuel injection valves that employ a strain-
type
actuator. For example, if the strain-type actuator is a piezoelectric
actuator, by
controlling the charge applied to the actuator the valve needle lift can be
commanded to the desired lift position. However, even with this approach
there can be variability of fuel flow from one injection event to the next
25 because the actual valve needle lift may not always accurately match the
commanded lift. Variability in the actual valve needle lift can be caused
by a number of factors, including, for example, one or more of variations
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in combustion chamber pressure, variations in fuel pressure, the effects of
differential thermal expansion/contraction within the fuel inj ection valve,
and component wear within the fuel injection valve. Accordingly, even
with a fuel injection valve that employs an actuator that allows lift control,
there can be factors that cause variability in the actual lift that can still
be large
enough to cause variability in the quantity of injected fuel.
[0012] Engine instability at idle and low load conditions can cause
higher engine fuel consumption, exhaust emissions, noise and vibration.
Accordingly, there is a need for an apparatus and method that provides a
more consistent means of controlling the quantity of fuel inj ected during
each inj ection event when an engine is idling or under low load conditions
and that improves combustion stability under such conditions.
[0013] For compression ignition engines that burn a gaseous fuel it
can be beneficial to shape the rate of fuel injection to begin an injection
event with an initial low mass flow rate, followed by a higher mass flow
rate until the end of the fuel injection event. An example of this is
disclosed in co-owned and co-pending U.S. Patent Application Serial No.
10/414,850, entitled, "Internal Combustion Engine With Injection Of Gaseous
Fuel". It can be difficult to operate a conventional fuel injection valve to
provide
the stepped flow characteristic that is needed to achieve this result. If a
fuel injection valve that provides a substantially constant mass flow rate
for a predetermined range of valve needle movement can be made so that
this constant mass flow rate corresponds to the initial low mass flow rate
for a stepped injection event, such a feature can be useful for improving
injection consistency and engine performance for all operating conditions
from idle through to full load.
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Summary of the Invention
[0014] A fuel injection valve is disclosed for introducing a fuel into
an engine. The fuel injection valve comprises:
a. a valve body that comprises a nozzle and. that defines a fuel cavity
5 disposed 'vithin the valve body; and
b. a valve needle movable within the nozzle between a closed position
at which the valve needle is seated against a valve seat associated
with the nozzle, and a fully open position at which the valve needle
is spaced furthest apart from the valve seat to allow the fuel to flow
10 from the fuel cavity and into the engine through the nozzle.
[0015] When the valve needle is positioned between a first
intermediate position proximate to the closed position and a second
intermediate position spaced from the first intermediate position, the valve
needle and the valve body are shaped to cooperatively provide a constant
15 flow area between the valve needle and the valve body. The constant flow
area restricts flow through the nozzle so that mass flow rate is substantially
constant for a range o:f valve needle movement with boundaries of the range
of movement defined by the first and second intermediate positions.
[0016] To reduce the variability in flow rate when the valve needle
20 is positioned between the first and second intermediate positions, the
constant flow area is preferably smaller than the open flow area between
the valve seat so that the constant flow area controls the fuel mass flow
rate through the fuel injection valve when the valve needle is positioned
between the first and second intermediate positions.
25 [0017] The constant flow area can be provided by an annular gap
between the valve needle and the valve body or by grooves formed in the
valve body or the valve needle. The raised portions between the grooves
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can act as guides for the valve needle to add consistency to the positioning
of the valve needle on the valve seat.
[0018] In preferred embodiments, the fuel injection valve further
comprises a strain-type actuator for directly actuating the valve member.
The strain-type actuator can comprise a transducer selected from the group
consisting of piezoelectric, magnetostrictive, anf~ electrostrictive
transducers.
An electronic controller can be programmed to send command signals to the
actuator to move the valve needle between the closed position and the fully
open position and to positions therebetween according to predetermined
wavefonns.
[0019] The fuel injection valve can further comprise an amplifier
disposed between the actuator and the valve member to amplify the strain
produced by the actuator to cause larger corresponding movements of the
valve member. The amplifier can be a hydraulic displacement amplifier,
I S or it can employ at least one Iever to amplify the strain mechanically.
(0020] In preferred embodiments, the fuel is introducible into the
fuel cavity in the gaseous phase. The fuel can be selected from the group
consisting of natural gas, methane, ethane, liqueified petroleum gas, lighter
flammable hydrocarbon derivatives, hydrogen, and blends thereof.
[0021] The valve needle can be an inward opening valve needle
whereby the valve needle is movable in an inward direction opposite to the
direction of fuel flow when moving from the closed position towards the
open position. In this embodiment the nozzle can comprise a closed end
with at least one orifice through which the fuel can be injected when the
25 valve needle is spaced apart from the valve seat. In preferred embodiments,
the nozzle comprises a plurality of orifices through which the fuel can be
injected when the valve needle is spaced apart from the valve seat and the
collective open area of the plurality of orifices is greater than the constant
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flow area. When the valve needle is in the fully open position, the collective
open area of the plurality of orifices provides the smallest restriction for
the
fuel flowing through t:he nozzle and thereby govc;rns the mass flow rate of
fuel flowing through t:he fuel inj action valve.
5 [0022] ~n another embodiment the fuel injection valve can further
comprise a third intermediate position spaced from the second intermediate
position, defining a boundary of a second range of valve needle movement
between the second and third intermediate positions. When the valve needle
is positioned between the second and third intermediate positions the valve
10 body and the valve needle can be shaped to cooperatively provide a second
constant flow area that restricts flow through the nozzle so that mass flow
rate is substantially constant but higher than the mass flow rate when the
valve needle is positioned between the first and second intermediate
positions.
15 [0023] 13y way of example, preferred embodiments are illustrated
and described of a fuel injection valve for injecting a fuel directly into a
combustion chamber of an engine. Without delaarting from the spirit and
scope of this disclosure, persons skilled in this technology will understand
that other arrangements for the vald°e body and the valve needle of the
fuel
20 injection valve are also possible. The scope of the disclosed fuel
injection
valve includes nozzles and valve needles that are shaped to cooperate with
each other so that, when the valve needle is positioned between a first
intermediate position proximate to the closed position and a second
intermediate position spaced from the first interrriediate position, a
25 substantially constant pressure drop occurs when the fuel is flowing
through
the nozzle so that mass flow rate is substantially constant for a range of
valve needle movement with boundaries of the range of movement defined
by the first and second intermediate positions.
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[0024] ~ method is provided of regulating fuel mass flow rate into
an engine through a nozzle of a fuel injection valve. 'The method comprises:
commanding a valve needle to move to av position between first and
second predetermined intermediate positions, which are between a closed
5 position and a fully open position; and
shaping the valve needle and the nozzle to cooperate with one
another to provide fuel passages through the nozzle that restrict fuel flow so
that mass flow rate through the nozzle is substantially constant when the
valve needle is positioned between the first and second intermediate
10 positions and the fuel is introduced, at a substanl;ially constant
pressure, into
a fuel cavity within the nozzle.
[0025] ~'referably the method further comprises commanding the
valve needle to the mid-point between the first and second intermediate
positions when the su'~stantially constant mass flow rate is desired. Because
15 there can be some variability between the commanded needle position and
the actual needle position, commanding the valve needle to the mid-paint
of the range of movement reduces the likelihood of the actual valve needle
position being outside of the range of movement defined by the
predetermined first and second intermediate positions. ~verall, this
20 reduces variability in the fuel mass flow rate dE;livered into the
combustion
chamber.
[0026] In preferred embodiments of the method, the substantially
constant fuel mass flow rate corresponds to the desired fuel mass flow rate
for idle or low load conditions. As indicated already, under these
25 conditions an engine is most susceptible to variations in fuel mass flow
rate because the required amount of fuel to be injected is already small,
compared to when the engine is operating under higher loads, and even
small variations in fuel mass flow rate can have an adverse effect on stable
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engine operation, with corresponding adverse impacts on engine
performance characteristics such as engine emissions, noise, and/or
efficiency.
[0027) In a preferred embodiment of the method, providing a flow
restriction within the rgozzle with a constant flog,- area when the valve
needle
is positioned between the first and second intermiediate positions regulates
the substantially constant fuel mass flow rate. Fuel mass flow rate can be
substantially and progressively increased by moving the valve needle from
the second intermediate position toward the fully open position.
[0028] The method can further comprise shaping the valve needle
and the nozzle to cooperate with one another to provide fuel passages
through the nozzle that restrict fuel flow so that vwhen the valve needle is
positioned between the second intermediate position and a third intermediate
position, which is provided between the second intermediate position and
the fully open position, fuel mass flow rate through the nozzle is
substantially constant but greater than fuel mass flow rate when the valve
needle is positioned between the first and secondl intermediate positions. In
this embodiment of the method, the fuel mass flow rate can be substantially
and progressively increased by moving the valve needle from the third
intermediate position l:oward the fully open position.
[0029] The method preferably comprises injecting the fuel from
the nozzle directly into a combustion chamber of the engine. By injecting
the fuel directly into the combustion chamber, the engine can maintain the
compression ratio and efficiency of an equivalent engine burning diesel
25 fuel. If the fuel is injected into the air intake system upstream of the
intake
valve, to avoid early detonation of fhe fuel it m<~y be necessary to limit the
amount of fuel injected and/or to reduce the engine's compression ratio.
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[0030] The present method is particularly suitable fog° fuel that is in
the gaseous phase when it is flowing through the nozzle. For example, the
fuel is selected from the group consisting of natural gas, methane, ethane,
liquefied petroleum gas, lighter flammable hydrocarbon derivatives,
hydrogen, and blends 'thereof.
[0031] A preferred embodirc~ent of the method further comprises
actuating a strain-type actuator to cause corresponding movements of the
valve needle. Strain-type actuators are particularly suited to implementing
the disclosed method because they can be controlled to command the valve
needle to move to and be held at any intermediate position between the
closed and fully open positions. The strain-type actuator preferably
comprises a transducer selected from the group consisting of piezoelectric,
magnetostrictive, and electrostrictive transducer:..
[0032] A method of regulating fuel mass flow rate into an engine
through a nozzle of a fuel injection valve by controlling valve needle
position, the method comprising:
increasing fuel mass flow rate from zero to a first value by moving
the valve needle from a closed position where it is urged against a valve
seat to a first interrrxediate position;
20 maintaining fuel mass flow rate substantially constant at about the
first value when the valve needle is positioned between the first
intermediate position and a second intermediate position, which is spaced
from the first intermediate position;
progressively increasing fuel mass flow rate beyond the first value
25 by moving the valve needle from the second intermediate position towards
a fully open position; and
increasing fuel mass flow rate to a maximum value by moving the
valve needle to the fully open position.
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[0033] In a preferred method, the first value is the fuel mass flow
rate that is commanded when the engine is operating under idle or low
load conditions.
[0034] 'The preferred method can further comprise commanding
the valve needle to move according to a stepped waveform with a
relatively low mass flow rate during a first step and a higher mass flow
rate during a second step and wherein the first value is the fuel mass flow
rate that is commanded for the first step.
Srief Descrimtion c~f the Dradvin~s
[0035] 'The drawings illustrate specific embodiments of the
invention, but should not be considered as restricting the spirit or scope of
the invention in any way.
[0036] Figure 1 is a schematic view of a directly actuated fuel
15 injection valve that is operable to inject a substantially constant
quantity of
fuel for a predetermined range of valve needle movement.
[0037] Figures 2A through 2C show schematic cross section views
of a valve nozzle and valve needle tip that could be employed, for
example, by the fuel injection valve of Figure 1. Figure 2A shows the
valve needle in the closed position. Figure 2B ;shows the valve needle
positioned in a region that provides a constant flow area thereby producing
a substantially constant flow rate for a range of needle movement. Figure
2C shows the valve needle lifted beyond the region of constant flow area.
Figures 2A through 2~C illustrate an embodiment of the features that can be
25 employed to make the fuel injection valve operable to inject a
substantially
constant quantity of° fixel for a predetermined range of valve needle
movement.
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[0038] Figures 2D and 2E show section views through the section
line marked D/l~ in Figure 2A. Figures 2D shows a simple concentric
circular arrangement that defines an annular constant flow area between
the valve needle and the valve body. Figure 2E provides an example of
another embodiment where a constant flow are<~ is provided by a plurality
of grooves formed in the valve body.
[0039] Figure 3 is a schematic cross section view of a nozzle that
comprises features for providing two different ranges of movement for an
inward opening valve needle, with each range a~f movement providing a
respective substantially constant flow rate determined by the constant flow
area provided within each range.
[0040] Figures 4A through 4C show schematic cross section views
of an embodiment of a valve nozzle for an outvcrard opening needle.
Figure 4A shows the valve needle in the closed position. Figure 4B shows
15 the valve needle positioned in a region that provides a constant flow area
thereby producing a substantially constant flow rate for a range of needle
movement. Figure 4C shows the valve needle lifted beyond the region of
constant flow area.
[0041] Figure 5 is a schematic cross section view of an outward
opening valve needle and a valve nozzle that cooperate with each other to
provide two ranges of valve needle positions that each provide a
substantially constant flow area whereby fuel mass flowrate is
substantially constant when the valve needle is ;positioned anywhere within
those ranges.
25 [0042] Figure 6 is a plot of the mass flow rate through a fuel
injection valve nozzle against valve needle lift. Two embodiments are
illustrated, one with a single range of movement that causes a substantially
constant mass flow rate and a second embodiment with two ranges of
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movement that cause respective substantially constant mass flow rates.
These embodiments are compared to a plot of the flow characteristics for a
conventional fuel injection valve.
[0043] Figure 7 is a plot of the commanded mass flow rate through
a fuel injection valve. A number of commanded shapes are shown which
can benefit from the consistency that can be achieved by employing the
disclosed nozzle and valve needle features to improve the flow
characteristics through fuel injection valves.
Detailed I)escri~tion of Preferred Embodiment s
[0044] The schematic views are not dram to scale and certain
features may be exaggerated to better illustrate their functionality.
[0045) Figure 1 is a schematic cross-sectional view of fuel
injection valve 100, which can be employed to introduce fuel into an
engine. Valve body 102 houses valve needle 1:10, actuator 120, and
transmission assembly 13U. Valve body 102 also defines fuel cavity 104,
which comprises fuel passages extending from coupling 106 and fuel inlet
108 through to valve seat I I2. Valve needle 110 is movable within nozzle
114 between a closed position at which valve needle 110 is seated against
valve seat 112 and a fully open position at which valve needle 110 is
spaced furthest apart from valve seat 112. When valve needle 110 is
spaced apart from valve seat I 12, fuel can flow from fuel cavity 104 into
the engine through nozzle 114. In the example illustrated by Figure l, fuel
exits nozzle 114 through orifices 116. In the case of an. outward opening
25 valve needle (see for example Figures 4 and 5), fuel can exit the nozzle
directly through the opening between the valve needle and the valve seat.
[0046] The disclosed features for influencing the flow
characteristics through a fuel injection valve are independent from the type
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of actuator employed to cause valve needle movements. Any actuator that
can be controlled to influence the speed of valve needle actuation andJor to
control valve needle position between the closed and fully open positions
can benefit from the disclosed arrangement. Far example, an
5 electromagnetically actuated fuel injection valve can employ the disclosed
features because the rate of opening for an electromagnetic valve can be
controlled to a certain degree by controlling the rate of force rise. That is,
using an electromagnetic actuator, the speed of valve needle movement
can be kept slow during the beginning of a fuel injection event, prolonging
10 the time when the fuel is introduced at a constant relatively low fuel mass
flow rate before the fuel mass flow rate increases during the later part of
the fuel injection event.
[0047] Tn preferred embodiments, injection valve 100 comprises a
strain-type actuator for directly actuating valve needle 110 and providing
15 the advantage of facilitating control over valve needle movements. A
directly actuated fuel injection valve is defined herein as one that employs
an actuator that can be activated to produce a mechanical movement that
directly corresponds to a movement of the valve needle. In such a directly
actuated fuel injection valve, the mechanical movements originating from
20 the actuator can be amplified by one or more mechanical levers or a
hydraulic amplifier, but the movements of the actuator always correlate to
corresponding movements of the valve needle. Tn the example illustrated
by Figure 1, transmission assembly 130 transmits movements from
actuator 120 to valve needle 110. Transmission assembly 130 comprises a
25 hydraulic displacement amplifier. mechanism that a~:~p:lifies the
mechanical
movements originating from actuator 120. In this example, actuation of
valvQ needle 110 occurs as now described. Actuator 120 can be activated
to produce mechanical movements in an axial direction to move base 122 'I
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and plunger 124 towards nozzle 114. Plunger 124 displaces hydraulic
fluid within amplification chamber I32, In the short time interval of an
injection event, the volume of hydraulic fluid within amplification
chamber 132 remains substantially constant. Since the hydraulic fluid is
substantially incompressible, to accommodate the fluid displaced by
plunger I24, valve needle I IO moves in the opposite direction, away from
valve seat 112, thus opening the valve 100 and initiating a fuel injection
event. The amount of amplification is predetermined by the relative end
areas of plunger i24 and the shoulder of valve needle 110, which are both
disposed in amplification chamber I32. That is, the higher tlae ratio
between plunger end area and valve needle shoulder area, the greater is the
needle stroke amplifac:ation.
[0048] Actuator 120 can be commanded to change the amount of
strain during an in~ecoion event to move valve needle 110 to a different
1S open position, or to reduce the strain to zero to end an injection event.
[0049] Spring; 126 biases valve needle 110 in the closed position
and helps to ensure that no spatial gaps form between actuator 120,
transmission assembly I30 and valve needle 110.
[0050] In the illustrated example, transmission assembly 130
further comprises hydraulic fluid reservoir 134. Compared to the time
interval of a fuel injection event, there are much longer periods of time
between injection evE;nts and when the engine is not running, when there is
sufficient time to allow some fluid flow between reservoir 134 and
amplification chamber 132 through the small gaps provided between the
25 adjacent surfaces of plunger 124, valve needle 110, and valve body 102
and conduits 136 and 138. Such flow between reservoir 134 and
amplification chambE;r 132 can compensate for leakage of hydraulic fluid
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and small dimensional changes between components that can be caused,
for example, by differential temperature expansion/contraction and wear.
[OOS1J Seals 137 and 139 seal against leakage of the hydraulic
fluid into fuel cavity 104, which is necessary when valve 100 is employed
to inject a gaseous fuel. If the fuel is a liquid fuel and it is conveniently
employed as the hydraulic fluid, seal 139 is not necessary.
[00S2] Strain-type actuators are generally controllable to produce
any amount of strain between zero and a maximum amount of strain that is
producible by a given actuator. 'That is, a strain-type actuator can be
commanded to move valve needle 110 to an intermediate po;9ition where it
can be held for a desired length of time. A controller can be programmed
to command the actuator to change the amount of strain so that valve
needle 110 is moved from the intermediate position to another open
position or the closed position. This allows the movements of valve
needle 1 I O to be commanded to follow a predetermined waveform, which
provides mare flexibility to control the fuel mass flow rate during an
injection event, and this flexibility can be employed to improve
combustion characteristics to increase performance or efficiency, and/or
reduce the exhausted emissions of undesirable combustion products such
as particulate matter or oxides of nitrogen or carbon, andlor nfeduce engine
noise.
[00S3] By wa.y of example, actuator 120 is depicted :schematically
in Figure 1 as a stack of piezoelectric elements for providing strain-type
actuation of valve needle 110. Persons skilled in this technology will
25 understand that other strain-type actuators, such as electrostrictive or
magnetostrictive actuators, can be employed to achieve the same results.
[00S4] While strain-type actuators can be commanded to produce a
desired strain, there are variable effects such as temperature, wear, fuel
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pressure, intake manii:old pressure and combustion chamber ~aressure, that
can influence valve needle position differently from one injection event to
another. Accordingly, even if an actuator is commanded to produce a
given strain that normally corresponds to a desired valve needle position,
5 the actual valve needle position may be different, and variances between
actual position and tine desired position can be significant enough to
reduce combustion efficiency, especially when the engine is at idle or
under low load conditions.
[0055] The features illustrated in Figure 2 through 5 show
10 embodiments of valve needles and valve bodies that are shaped to
cooperatively provide. a constant flow area between the valve; needle and
the valve body when the valve needle is positioned within a range of
movement when the cooperating surfaces are held opposite to each other.
This constant flow area restricts flow through the nozzle so that fuel mass
15 flow rate is substantially constant. By commanding the valve needle to a
position near the mid-point of this range, fuel mass flow rate is made
substantially insensitive to small variations in needle position. All of the
illustrated embodiments operate on the same principles and each can be
advantageously employed to reduce variability between the commanded
20 fuel mass flow rate and the actual fuel mass flow rate for idle and low
load
conditions, as well as higher load conditions when a stepped injection
profile is commanded.
[0056] With reference now to the illustrated embodiment of
Figures 2A through 2C, a valve needle and nozzle arrangement is
25 schematically shown,. This arrangement can be employed, for example,
with the fuel injection valve of Figure 1. Accordingly, the same reference
numbers used in Figure 1 are used to designate similar features in Figures
2A through 2C. only the tip portion of nozzle 114 is shown, with valve
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body 102 defining a portion of fuel cavity 104 that surrounds valve needle
110. Figures 2A through 2C each depict the same embodiment, but with
each figure showing valve needle 110 in a different position.
[0057] In Figure 2A, valve needle 110 is shown in the closed
position, seated against valve seat 112 so that fuel can not flow through
orifices 1 I6. To begin a fuel injection event, valve needle 110 is movable
in the direction of arrow 150. Valve needles such as the one shown in
Figures 1 through 3 are movable away from a valve seat and in a direction
opposite to the direction of fuel flow are known as inward opening valve
needles. In Figure 2E. valve needle 110 has been lifted away from valve
seat 112 to an open position. In Figure 2B a portion of the vertical side
surface of valve needle 110 is opposite to the vertical wall of valve body
102 provided by shoulder 103. The parallel and opposite vertical surfaces
provide a flow restricting gap therebetween, identified by dl . This gap is
sized to provide a flow area that restricts fuel flow through nozzle 114 to a
substantially constant fuel mass flow rate for a range of valve needle
movement as long as a portion of the vertical side surface of valve needle
110 is opposite to the vertical wall provided by shoulder 103. That is,
because the cooperating vertical surfaces that farm the gap are parallel to
one another, the size ~of the gap remains constant for a range of valve
needle movement. In Figure 2C valve needle 110 has been lifted beyond
the point where the vertical surfaces of valve needle 1 I O and shoulder I03
are opposite to each other. Beyond that point, the flow area between valve
needle 1 IO and valve body 102 increases as valve needle 110 moves
25 further away from valve seat 112. Valve needle 110 can be lifted further
from the position in Figure 2C until it reaches a fully open position. With
a nozzle arrangement such as the one shown in Figure 2C, a maximum
fuel mass flow rate can be limited by the restriction of the open area
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provided by orifices 116. if such is the case, lifting the needle beyond the
point where fuel flow becomes choked by the orifices does not result in
further increases in the fuel mass flow rate.
[0058] Reference is now made to Figures 2D and 2E, which show
5 two different embodiments of a section view through the section line
marked D/E in Figure 2A. Figures 2D and 2E show that the constant flow
area can be made in different shapes without departing from the spirit of
the present disclosure. Figure 2D shows a simple concentric circular
arrangement that defines the constant flow area between valve needle 110
10 and the valve body 2C)1. In Figure 2E the constant flow area is provided
by a plurality of grooves formed in the valve body 102. By way of
example, the grooves are shown with a bottom detned by a diameter
concentric with the opposite walls of valve needle 110, and shoulder 103
provides raised surfaces between the grooves. Persons skilled in this
15 technology will understand that the grooves and raised surfaces between
the grooves can take different shapes without departing from. the scope of
the present disclosure. While Figures 2D and 2E are introduced with
reference to the embodiment of Figure 2A, these examples of the shape for
the constant flow area are applicable to all of the embodiments disclosed
20 herein. With some embodiments, the grooves can be formed in the valve
needle surface instead of the valve body surface.
[0059] Another embodiment of a nozzle with an inward opening
valve needle is shown in Figure 3. Valve body 302 and valve needle 310
define the shown portion of fuel cavity 304. Valve needle 310 is in the
25 closed position, where it is urged into fluidly sealed contact with valve
seat
312. Orifices 316 provide an outlet for the fuel to exit the valve body
when valve needle 310 is lifted away from valve seat 312 in the direction
of arrow 350. The difference between this embodiment and the
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embodiment of Figures 2A through 2C is that valve body 30a? is provided
with two shoulder areas 303 and 303A, which each provide a vertical
surface parallel to the vertical surface of valve needle 310. Shoulder 303
in Figure 3 is similar to shoulder 103 in Figures 2A through 2C. Shoulder
303A provides a second parallel surface area that provides a larger
constant flow area when the vertical surface of valve needle :310 is
opposite to it. Accordingly, the nozzle arrangement of Figure 3 can
provide two ranges of needle movement where the fuel mass flow rate can
be substantially constant. A Lower substantially constant fuel mass flow
rate is provided when the vertical surface of valve needle 310 is opposite
to the vertical surface of shoulder 303 and a higher substantially constant
fuel mass flow rate is provided when the vertical surface of ~ralve needle
310 is opposite to the vertical surface of shoulder 303A.
[0060] Figures 4A through 4C illustrate yet another embodiment of
a valve body and valve needle arrangement that provides a substantially
constant fuel mass flow rate for a predetermined range of valve needle
movement. In Figure 4A, valve needle 410 is shown in the closed
position, seated against valve seat 412 so that fuel can not flow through
nozzle 414. To begin a fuel injection event, valve needle 410 is movable
in the direction of arrow 450. Valve needles such as the one shown in
Figures 4 and S, which are movable away from a valve seat and in a
direction parallel to the direction of fuel flow are known as outward
opening valve needles, and the fuel injection valves that employ outward
opening valve needles are sometimes referred to as poppet valves. In
25 Figure 4B valve needle 410 has been lifted away from valve seat 412 to an
open position within the range of valve needle movement where a
substantially constant fuel mass flow rate can be injected. In Figure 4B a
portion of the vertical side surface of valve needle 410 provided by
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shoulder 403 is opposite to the vertical wall of valve body 402. The
parallel and opposite vertical surfaces provide a gap therebet<ween,
identified by dl . Like the other embodiments, this gap is sized to provide
a flow area that restricts fuel flow through nozzle 414 to a substantially
constant fuel mass flow rate for a range of valve needle movement as long
as a portion of the vertical side surface of valve needle 410 is. opposite to
the vertical wall provided by valve body 402. In Figure 4C valve needle
410 has been lifted beyond the point where the vertical surfaces of
shoulder 403 and valve body 402 are opposite to each other. beyond that
point, the flow area between valve needle 410 and valve body 402
increases as valve needle 410 moves further away from valve seat 412.
Frorn the position in 1?igure 4C, valve needle 410 can be lifted further in
the direction of arrow 450 until it reaches a fully open position.
[0061] Another embodiment of a nozzle arrangement with an
outward opening valve needle is shown in Figure S. Valve body 502 and
valve needle S 10 define the shown portion of fuel cavity 504. Valve
needle 510 is in an open position, where it is has been lifted from the
closed position in direction of arrow SSO. The difference bei;ween this
embodiment and the embodiment of Figures 4A through 4C is that valve
needle 510 is provided with two shoulder areas 503 and 503.x, which each
provide a vertical surface parallel to the vertical surface of the opening
through valve body 502. Shoulder 503 in Figure 5 is similar to shoulder
403 in Figures 4A through 4C. Shoulder 503A provides a second parallel
surface area that provides a larger constant flaw area when the vertical
25 surface of the opening through valve body 502 is opposite to~ it.
Accordingly, the nozzle arrangement of Figure 5 can provide two ranges
of needle movement where the fuel mass flow rate can be substantially
constant. A lower substantially constant fuel mass flow rate is provided
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when the vertical surface of shoulder 503 is opposite to the vertical surface
of the opening through valve body 502 and a higher substantially constant
fuel mass flow rate is provided when the vertical surface of shoulder 503A
is opposite to the vertical surface of the opening through valve body 502.
In the illustrated example, the difference in the constant flow areas for the
two ranges of needle movement are defined at least in part by the
differences in dimensions dl and d2. Persons skilled in this 'technology
will understand that other embodiments could achieve the same result
without departing from the spirit and scope of the present disclosure. For
10 example, the flow area can be increased without increasing tile gap
dimension by widening grooves, such as the ones shown in Figure 2E to
increase the constant flow area for the second range of valve needle
movement.
[0062] Figure 6 is a plot of fuel mass flow rate Q versus needle lift
L. Line 600 shows a curve that is representative of conventional fuel
inj ection valves. As depicted by Iine 600, with ~ conventional fuel
injection valve, increases in needle lift cause progressive increases in fuel
mass flow rate until maximum fuel mass flow rate Qc is reached, for
example, when flow is choked by the restriction provided by the nozzle
orifices or another re striction provided elsewhere in the fuel injection
valve. The slope of line 600 flattens out as it approaches the choked flow
rate so small variations in lift when the valve needle is commanded to near
the fully open position do not have a significant impact on fuel mass flow
rate.
25 (0063] For a :duel injection valve that controls needle lift to control
fuel mass flow rate, with a conventional fuel injection valve., if Qa
represents the desired fuel mass flow rate for idle or low load conditions,
the needle is commanded to be lifted by distance L1 to deliver the desired
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flow rate. Because of the steep slope of line 600 near lift L1, even small
deviations from position L1 can result in a significant variation in the
actual fuel mass flow rate.
[0064] Solid line 610 shows a curve that is representative of a fuel
injection valve that erriploys the features ofthe present disclosure. For
example, at idle or low load conditions, the valve needle can be
commanded to a positian at the mid-point between Ll and L2. Because
the slope of line 610 between L1 and L2 is much flatter than the scope of
line 600 for the same range of valve needle movement, the fuel injection
10 valve of line 610 can be operated with improved consistency to improve
engine performance, efficiency, and/or reduce emissions of unwanted
combustion products like particulate matter and oxides of nitrogen or
carbon, and/or reduce. engine noise. The embodiments illustrated in
Figures 2 and 4 show examples of fuel injection valves that can provide
15 one range of valve needle movement where fuel can be injected with a
substantially constant fuel mass flow rate. The range of movement
between L1 and L2 represents the range of valve needle movement that
corresponds to when the parallel vertical surfaces of the valve needle and
the valve body cooperate with one another to define the gap dimensioned
20 dl. iUhen the valve needle moves further away from the valve seat and
beyond this range, the fuel mass flow rate progressively increases along a
steeper slope until the maximum fuel mass flow rate is reached.
[0065] Broken line 620 plots the flow characteristics for a fuel
injection valve such as the ones illustrated in Figures 3 and '. These fuel
25 injection valves provide two ranges of valve needle movement where the
fuel mass flow rates are substantially constant. The range of. movement
between L3 and L4 represents the range of valve needle movement that
corresponds to when the parallel vertical surfaces of the valve needle and
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the valve body cooperate with one another to define the gap dimensioned
d2. When the valve needle is lifted to a position between L3 and L4,
because the slope of line 620 is relatively flat, there is very little
variation
from commanded fuel mass flow rate Qb.
[0066] Figure 7 is a plot of a number of examples of the
corr~manded mass flo'u rate versus time through a fuel injection valve for a
single fizel injection event. Each of the illustrated commanded shapes can
benefit from the consistency that can be achieved by employing the
disclosed nozzle and valve needle features to improve the flaw
characteristics through a fuel injection valve. In this plot, Qc; again
represents the maximum fuel mass flow rate. Line 710 corresponds to a
relatively small fuel mass flow rate, Qa, such as what could be
commanded for idle or low load conditions. The benefits have already
been described of being able to reduce the variability in the duantity of fuel
introduced into the engine from cycle to cycle under idle and low load
conditions. It can als~ be desirable to introduce the fuel directly into an
engine combustion chamber in a stepped waveform, where initially a
smaller fuel mass flow rate is injected, such as shown in Figure 7 by Qa or
Qb, followed by higher fuel mass flow rate such as shown by line 730. A
fuel injection valve with two ranges of valve needle movemf,nt that
provide substantially constant fuel mass flow rate can employ a controller
that is programmed to use a waveform such as the one shown by line 710
for idle conditions and the waveform of line 720 for light load conditions
or in a stepped waveform the beginning of line 710 until t2 and then the
25 line of 720 after t2, or for higher load conditions after t2 line 730 can
be
selected. Persons skilled in this technology will understand that other
combinations are possible such as the beginning of line 720 until t2
followed by line 730 to inject even more fuel into the engine.. In some
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operating conditions it can also be beneficial to provide a downward step
when the valve needles is moving from the open position to th.e closed
position. The benefit of a fuel injection valve with the disclosed features
is that the constant flow areas can be selected to provide more consistent
fuel mass flow rates at predetermined steps in the waveforms employed to
control needle movements, reducing cycle-to-cycle variability when the
engine is operating.
[0067] The disclosed fuel injection valve was developed for
gaseous fuels, but the same features can be beneficial for fuel injection
valves that inject a liquid fuel. However, for a liquid fuel, there are
additional considerations that must be taken into account such as
cavitation and maintaining adequate pressure for atomization of the fuel.
Cavitation can occur when a sudden pressure drop lowers the fuel pressure
below the vaporization pressure and some of the fuel is vaporized befare
the fuel is discharged from the injection valve. Problems associated with
cavitation and atomization can be avoided, fvr example, by employing one
or more of the following strategies: (l) introducing the fuel to the fuel
inj ection valve with a.n initial pressure that is high enough to ensure that
fuel pressure remains above the vaporization pressure and adequately high
after the restricted flow area to atomize the fuel when it exits the fuel
injection valve; (ii) sizing the restricted flow area to Limit the; pressure
drop
so that fuel pressure is not reduced to less than the vaporization pressure or
the minimum pressure required to atomize the fuel upon exiting the fuel
injection valve; (iii) providing a smooth entrance into the restricted flow
25 area to reduce turbulence that can cause low pressure regions; and (iv)
manufacturing the nozzle and valve needle from materials that will not be
damaged by exposure to the conditions associated with cavitation. With
liquid fuels, it is possible to employ the disclosed features and realize
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many of the same benefits that can be achieved with gaseous fuels. For
example, it is possible: to achieve more stable performance ardd reduce
engine noise under idle and low load conditions by reducing variability in
the quantity of infected fuel.
S [006] ~hil.e particular elements, embodiments and applications
of the present invention have been shown and described, it will be
understood, of course, that the invention is not limited thereto since
modifications may be made by those skilled in the art without departing
from the scope of the present disclosure, particularly in light of the
10 foregoing teachings.
