Note: Descriptions are shown in the official language in which they were submitted.
` ~ ~Z8~
-- 2 --
DELIVERY OF METERED_QUANTITIES OF FUEL TO AN ENGINE
This invention is directed to the metering and
delivery of fuel to an internal combustion engine, and in
particular concerns those systems employing a pulse o~ gas
to deliver and/or inject a metered quantity of uel. The
invention has particular applicability to the fueling of
engines for transport vehicles, which may experience frequent
and substantial transient load conditions.
There is an increasing requirement for less expen-
sive, and more fuel efficient, fuel injection systems forinternal combustion engines. Conventional fuel injection
systems have previously required a high pressure fuel pump,
and high differential pressure metering apparatus, in order
to achieve an acceptable degree of fuel atomisation and hot
fuel handling ability. Both these requirements result in a
high cost of componentry due to the high standard of
engineering required in production, the close tolerances on
manufacturing dimensions, and use of expensive materials of
construction.
The use of pneumatic fuel metering was described
in the SAE technical paper 820351 by Mackay, and further
~ ` details may be found in United Kingdom Patent Nos. 2,018,906
- and 2,102,50I and Canadian Patent Nos. 1,183,048 and
1,187,355. Such u~e significantly alleviates the problems
deacribed a~ove.
In the methods of pneumatic fuel metering and
injection described~in the above documents, a metered
quantity of fuel located in a chamber is expelled from that
chamber by a pulse of gas at high pressure for delivery to
the engine. Such delivery is preferably via fle~ible tubing
to the engine's inlet manifold but may alternatively be
delivered directly into the combustion chamber. Existing
systems operate by providing gas at an elevated pressure
upstream of a valve at the gas inlet port of the chamber,
and opening that;valve in response to instruction from a
programmed electronic controller. The period of valve opening
has previously been maintained constant for all metered quan- l
'. .
:
~.,;~, X
, . , : . .. : - . . . , . : ,
,. , : , , . , , ., . :, ~ , . . .
- i. . . . . , . . . :
~lZ87~33
-- 3 --
tities of fuel to be delivered from the chamber by the gas
pulse, the system being designed so the period is sufficient
to deliver the required metered quantity of fuel at maximum
fuel demand of the e~gine. The period of valve opening was
controlled by a constant width pulse from the electronic
controller.
However, for acceptable operation of a given
engine, the system must be able to handle a wide range of
fuel quantities. Under steady state operation (i.e. constant
speed and load) a fuel metering and delivery system requires
a turn-down ratio of about 5 to 1, but on abrupt load
increases the engine can require, for a very short period,
up to twice as much fuel than that at wide open throttle.
Current evidence suggests that although a constant
gas pulse width is sufficient to expel the required amount
of fuel from the chamber, the quantity of air actually
delivered with the metered quantity of fuel significantly
decreases with increased metered fuel quantities. This
decrease in air quantity is thought to be due to inertia and
viscosity~effects of the increased quantity of fuel, and has
a detrimental effect on the~quantity of fuel actually
delivered,;the~quality ~of~the fuel air mixture preparation
and~spray~ pattern delivered to the engine.
~ t is thè~object~of the present invent~ion to
provide`;a~meth~od of delivering fuel to an engine by the use
of a compres~se~d ga;s~ which will~give~improved engine response
in transient~ load conditions.~
The~present invention proposes a method of deliver- -
ing~fuel to~an~engine;by the~;a;dmission~of compressed gas to
30 a chamber~to~displace~a metered~quantity of fuel~therefrom,
~and~var~ying~the~mass~of gas admitted with variations in the
fuel d~emand~so that~as~the fuel demand increases the mass of
~gas~increases.~
The~increaslng of~the`~mass of gas admitted to the
3;5 ~chambe~r~to~di~sp~lace~the~metered quantity of fuel, as the
quant~ity~of fuel increases~, results in additional energy per
ùnit~weight af~foe~ `be~ing~ava~ilable~to~displace the fuel ~
from~the~metering~chamber;and~transport the fuel to and ~:
:,: ' '.-.' : : ' .. ' ! ' . ' ,
12~S33
through the injection nozzle.
Also the increased mass of gas will assis~ in the
atomisation and spray forma~ion of the fuel issuing from the
nozæle. Subject to the degree of increase in the gas mass
relative to the fuel quantity, the specific energy remaining
in the gas at the nozzle may also increase with the increase
in fuel quantity, and if not increased should at least be
maintained substantially constant for the major part o the
range of fuel quantities within normal operating conditions.
The variation of the gas mass may be in accordance
with a linear relation to the variation in fuel quantity,
or any other selected relation.
The mass of gas delivered to the metering chamber
is influenced by the pressure and temperature of the gas at
entry to the metering chamber. However, from practical consi-
derations it is not convenient to vary either the pressure
or temperature, particularly having regard to the requirement
of effecting~the variation in a time interval of a few milli-
seconds. The~most convenient means of varying the mass of
gas lS to vary the time period during which the gas is
admitted~to the~metering;chamber.
More speclficaily there is provided~a method of
dellvering fuel to~an~engine comprising establishing a ~ -
meterèd quantity of~fuel in a chamber, said chamber having '
25 à gas,supply:po~rt~and~a fuel delivery port, and displacing~ ,
the~fuel from~s~aid~chamber through said fuel delivery port ,'
and~delivérlng~the~fuel~through~a nozzle~ to the engine, said
~` displacement~and deliv~ery of the ~fuel being effected by
~admlsslon~of~gas~to~the chamber thro~ugh said gas supply ~- '
30 ~ port,,~wherein~the~,mass of gas~admi~tted~is varied in accord-
~ance~wlth~the~fùel;demand of said~engine;.
As~i~s known, when a~fluid~and particularly a liquid
~ flows~through~a~;~condult~a;~layer of~the liquid is formed on
; ` ~the~ internàl-surface of the~conduit. The thickness of the
35 ~ ayer ls dé~pendent on~a~numbe~r of facto~rs including the
vis~cos~i~,ty~of~ the~ iquld, the~ vel~ocity of flow, and the `~ -
surface~f~inish~of~the conduit. As the velocity of the liquid ~-
decreasës'the-~thlckness'of'~the~layer increases, and thus in
~'., ~' ~' . ' ; , '.. ' ' i . ' ' ' ' ' ' ' "
~Z8~S33
-- 5 ~
the fuel metering systems of the type under consideration,
if the velocity of the fue]. delivery decreases the quantity
of fuel in the stationary layer increases.
It is therefore seen that if there is an increase
in the fuel quantity without a corresponding increase in the
gas mass propelling the fuel, a portion of the increase in
fuel quantity may not be delivered to the engine, but is
consumed in increasing the stationary layer. Accordingly, by
increasing the mass of air propelling the fuel as the fuel
quantity is increased, a decrease in fuel velocity may be
avoided and the thickness of the stationary layer remains
substantially constant.
It is possible to reduce the thickness of the
layer if the increase in the air mass i5 sufficient to
increase the velocity of the fuel. This can be beneficial in
two ways. Increasing the gas mass without an increase in the
metered quantity of fuel will increase the fuel velocity and
consequently reduce the layer thickness. In this~way a
limited increase in fuel quantity delivered to the nozzle
can be achieved~without changing the actual metered
quantity. This~ manner of increasing fuel supply to the
engine can be~useful where the fuel demand increase is
relatlvely~small and of short duration.
Sècondly, if the increase in the gas mass is asso-
25 ciated with an~lncrease in~metered quantlty of~fuel, and is -
sufficient to increase~the overall fuel velocity, then a
reductlon~;of;the fuel layer thlckness may result, thus
further increasing the~quantity of fuel~delivered through
the~nozzle.`This may be used to~advantage when there is a
large~or~rapid inc~reasé~;in the fuel demand.
The~quantity of fuel may be metered upon introduc-
tion~to~the;~chamber,~;or may be metered by and/or during the
c~ourse~of~ th~e~admlss~lon of~gas to the chamber.
T~he~invention may be more readily understood from
35~ ;the~followi~ng~;exàmples, illustrated by the accompanying
drawings,;~of practlcal~arrangements of metering and injecting
fuel~ ;In~thê drawings "~
-- 6 --
Figure 1 shows a fuel metering apparatus for use
in the present invention.
Figure 2 shows a sectional view along 2-2 in Figure
- 1, with the addition of fur~her metered fuel delivery appara-
tus.
Figure 3 is a logic diagram of the operation
of an electronic controller to regulate the mass of gas
available to deliver the fuel.
Figure 4 is a diagram illustrating the variation
in the period of gas admission with fuel demand.
Figures 5a to 5d inclusive illustrate variations
to fuel quantity delivered in relation to gas mass.
With respect to Figures 1 and 2, the metering
apparatus shown comprises a body 110, having incorporated
therein four individual metering units 111 arranged in side
by side relationship. This apparatus is thus suitable for
use with a four cylinder engine, with each metering unit 111
dedicated to a separate cylinder. The nipples 112 and 113
are adapted for connection to a fuel supply line and a fuel -~
return line respectively (not shown), and communicate with
respective fuel supply and return galleries 60 and 70
~` provided within the body llO for the supply and return of
fuel from~each of the metering units lll
~Each metering unit 111 is provided with an indivi-
dual fuel~delivery~nipple 114 to which is connected a respec-
~tive metered~fuel~delivery conduit 108 which conducts theindividually metered~quantities of fuel to an injector nozzle
18 (Flgure 2). The n~ozzle is located at a suitable position
to deliver the fuel~to the engine, such as inserted in the
inlet~manifold of the engine near the respective cylinder
: air~inlet valve. Further details of the apparatus are given
in~our~abovementioned Canadian Pa~ent No. 1,183,048.
~ The body~llO is preferably positioned close to the
inj~ector~nozzle 18,~and the metered fuel delivery conduits
; ~108~arè~suitable tubing of approximately 1.8mm diameter, and
from lO~to 40~cm in length varying with the distance to each
` cylinder. ~ ~ ~
-.,~ ,: . . : ., , : ,. ............ . .......... . .
- , . . ~ , . . . . .
~ 7~3
-- 7 --
Figure 2 shows in section one metering unit 111
having a metering rod 115 extending into both the air supply
chamber 119 and metering chamber 120. Each of the our meter-
ing rods 115 pass through the common leakage collection
chamber 116, which is formed by a cavity provided in the
body 110 and the coverplate 121 attached in sealed relation
to the body 110. The function and operation o the leakage
collection chamber 116 is no part of this invention and is
described in greater detail in the abovementioned
Canadian Patent No. 1,183,048.
Each metering rod 115 is hollow, and is axially
slidable in the body 110, the extent of projection of the
metering rod into the metering chamber 120 being varied to
adjust the quantity of fuel displaceble from the metering
chamber 120. The valve 143, at that end of the metering rod
located in the metering chamber 120, is supported by the rod
143a and normally held closed by the spring 145, located
between the upper end of the hollow rod 115 and valve rod .--
143a. The flow of air through the hollow bore of the metering
rod 115 from the air supply chamber 119 to the metering
chamber 120 is controlled by the valve 143. Upon the pressure -
in the air supply chamber:ll9 rising to a predetermined value :
the valve 143 is opened to permit air to flow from air supply
chamber 119 to the metering chamber 120 through hollow rod
115, to displace the fuel from the metering chamber 120.
The quantity of fuel displaced by the air is that -
fuel located in the metering chamber 120 between the point
of entry of the air to the metering chamber, and the point
of discharge of fuel between the air admission valve 143 and
3~ the delivery valve 109 at the opposite end of the metering
chamber 120.
~ Each of the metering rods 115 are coupled to the
crosshead 161, and the crosshead is coupled to the actuator
rod ~l60 which is slidably supported in the body 110. The
ac:tuator:rod 160 is:coupled to the motor 169, which is
controlled in response to the engine fuel demand, to adjust
the extent of projection of the metering rods 115 into the
` metering chambers 120, and hence the position of the air ;::
admission valves: 143 so, the metered quantity of fuel ~:~
: . i , . . . . . .
., . ., ; .;., . ;' : ' ., ' ' , '', ' ~ , ' ' -:' ' .',
1~75~3
delivered by the admission of the air is in accordance with
the fuel demand. The motor 169 may be a reversible linear
type stepper motor such as the 92100 series marketed by
Airpax Corp.
S The fuel. delivery valves 109 are each pressure
actuated to open in response to the pressure in the metering
chamber 120, when the air is admitted thereto from the air
supply chamber 119. Upon the air entering the metering
chamber 120 through the valve 143, the delivery valve 109
also opens, and the air will move towards the delivery valve
displacing fuel from the metering chamber through the
delivery valve. The air admission valve 143 is maintained
open until suficient air has been supplied to displace the
fuel between the valve 143 and 109 from the chamber, an-d to
provide additional air to transfer the fuel through the
conduit 108 to the nozzle 18, and to atomisation the fuel
as it is delivered through the nozzle.
: Each metering chamber 120 has a respective fuel
inlét port 125 and a fuel outlet port 126 controlled by res- -
pec:tive valves 127 and 128~to permit circulation of fuel from
the~inlet~gallery~60, through the:metering chamber 120, to
the outlet~gallery 7;0.~Each of the valves 127 and 128 are
~;` connected~to~the~respective diaphragms 129 and 130. The
~ ~valves~:~12~7;~and:12~8:are spring-lo~aded to an open position,
`~ 25 and~are~clo~se~in~response~:to the application of air under
. ~ pressure to~t:he:respect~ive~di~aphragms 129 and 130 via the
dl~aphr~agm~cavl~tl:es~ 31~and~i32. E~ach of;the~diaphragm cavi-
ties~;~are~:in~constant communication with the air conduit 133, `~
~ and~the~;~:conduit 133~is in constant communication with the
: : 30~a}r s`upply~cha~mber~119~by ~the~c~ondul:t~135~.
Thus~ when~alr und`er pressure is admitted to the
.ai:r~supply:chamber~:ll9:and hence to the metering chamber 120
~to:~effect~de~livery of fuel, the air als~ acts:on the
diaphràgms~129~ ànd.~130~to~cause the:valves 127 and 128 to
35~clos~e the~:fusl~inl5t~and outl-r: p,rts ;1~5 and~126.
:. . :: . : : : . , . , : .
~2~ii33
- 9
The control of the supply of air to the chamber
119 through conduit 135, and to the diaphragm cavities 131
and 132 through conduit 133, is regulated in time relation
with the cycling of the engine by the solenoid operated valve
150. The common air supply conduit 151, connectable to a
compressed air supply via nipple 153, runs through the body
110 with respective branches 152 providing air to the respec-
tive solenoid valve 150 of each metering unit 111.
Normally the spherical valve element 159 is posi-
tioned, under action from springs 170, to prevent the flowof air from conduit 151 to conduit 135, and to vent conduit
135 to atmospheric via vent port 161. When the solenoid is
energised the force of the spring 170 acting on the valve
element 159 is relieved, and the valve element is displaced
by the pressure on the air supply to permit air to flow from
conduit 151 to conduits 135 and 133.
The timing of the energizing of the solenoid 150
in relation to the engine cycle may be controlled by a suit-
able sensing device 171, activated by a rotating component
of the engine, such as the crankshaft or flywheel 172 or any
other component driven at a speed directly related to engine
speed.~A sensor~suitable for t~his purpose is an optical
switch including an infra-red source and a photo detector
with Schmitt trigger.
~ Previously it has been proposed that the duration
of energization of the solenoid 150 be a fixed period,
independent of~fuel quantity to be delivered and engine
speed. This fixed period was selected to suit the maximum
fuel~demand when the engine is operating at maximum engine
30 ;speed.~
The most convenient manner of controlling the
~operation of the~solenoid 150 is an electronic controller,
~which~provides~a~pulse~of electrical energy of fixed duration
to~the~solenoid~l~rrespective of the engine fueling require-
35~ments.~ However, in using that form control in practice, ithas~-;been~found that the~actual quantity of air passed with
`~the~fuel thr~ough~the~lnjector nozzle 18 per fuel delivery
:
- 10 -
tends to reduce with increasing fuel delivery levels.
This is believed to be due to changes in inertia
and viscosity effects arising with the increased fuel level.
This can be compensated for by the present invention by
increasing the length of time the electrical energy is
applied to the solenoid 150 at the higher fuelling levels,
thus increasing the time during which gas enters the meter-
ing chamber 120 and so increasing the mass of air available
to pass along the fuel conduit and through the delivery
nozzle.
Figure 3 is a logic diagram representing a typical
mode of operation of the electronic controller 192 (Figure
1) to effect variation of the period that the solenoid 150
is energised in proportion to the metered quantity of fuel
to be delivered to meet the engine fuel demand. The control-
ler 192 is programmed with the required relationship between
metered fuel quant~lty and air mass per injection cycle.
As sh~own in Figure~l the actuator rod 160 carries
a wiper arm I90 which co-operates with a stationary resis-
tance strip l91 mounted in the body 110. The wiper and resis-
- tance~strip forming a feed back potentiometer 198~ The
~a~ctuator~`rod 160~ls coupl~ed~to the metering~rods 111 and
varies~the extent~of~projection of the metering rods into
the metering chambers 120, and hence varies the metered
~5 quantity~of~fue;1;dell~vered~.~;Accordingly;the; position of the
wipe~r arm 190 on the resistance strip l91 and hence the out-
put~of~the~`fee~d-ba~ck~potentlometer is dlrectly proportional
~to the~metered~quantlty of uèl~ belng delivered.
The~electronic con~roller 192 is programmed to
30 ~recelve~at~a~regul;ar lnte~rval~of voltage reading from the
p`ot~ent~iometer~198~and~thereby determine the position of the
~actuator~rod 160 and~hence the size of the metered quantity
of fuêl,;~The readings~from ~the ~resistor are conveniently
made`~a~t~hal~ milli-second intervals.
35~ R~e~ferring~still t~o Figure 3, having received the
voltage~r~eading~from~the~potentiometer the controller 192
~8~S3~
determines the period of energization of the solenoid 150
required for the metered quantity of fuel corresponding to
the position of the actuator rod 160, If at the time of the
controller making the deterrnination the engine is in that
S part of the engine cycle when fuel is being delivered, then
the controller will make an adjustment to the rernaining
period of energization. If as a result of this adjustment
the period of energization is reduced to zero, then the
controller will switch off the solenoid energizing channel
so that delivery of fuel and gas will cease. However, if the
remaining period is not reduced to zero then the solenoid
will continue to be energized and fuel and gas will continue
to be delivered. At the next half milli-second period the
sequence is~repeated.
Reverting to the determination of the period of
; energizing of~the solenoid, if at that time the engine is
-~ not in that part of its cycle when fuel is to be delivered,
` the~newly determined period of energization is stored. If
within the then current half milli-second interval the
:
engine`enters thé~part of its cycle when fuel is to be
,
delivered,~then the so~lenoid will be energized for the newly
determlne'd`period.~In~the~event that the engine does not
~enter th~e~part of its cycl~e for the delivery of fuel during
the~half~milli-second~interval, then at the end of that
peri~od;the`~sequence~is~repeated~as~above explained.
Comme~rcial~l~y~avallable componentry can be arranged
and~programm'ed~to~per,form~the,;~functions requi;red to fulfill
the;~above~discussed logic d'iagram. Also,other factors may
be~introduced~t~o~vary~the~period~that the solenoid is
~O:~energized~ In~automotlve~applications one factor that may be~
taken~lnto~ac~count,;ls~the~`voltage of the electrical energy
source~to~operat~e~the~solenoid.
T~he~voltage o~f~the~battery~provided ln an auto~
mobile~m'ay~ vary~signi~fi'cant~ly;~under operating conditions ~~
3~5 -~fr~`'m=the~nomi;nal~ rated~ 2~volts~. Slgnificant drop in voltage
,can~occur~a~t~times~when~high `loads are applied to the ~ ~`
. ~ : . . . ; . . : . . . .
lZ~7S33
battery, such as cranking the engine during start-up. In
order to compensate for this drop in voltage available to
energize the solenoid, the period of energization may be
extended.
The electronic controller 192 may thus incorporate
a function to compare the actual voltage available to the
solenoid against the battery rated voltage and if the actual
voltage is below rated, an extension of the period of
energization of the solenoid may be made. The degree of
extension of the period relative to the drop in voltage may
be pre-programmed into the electronic cont~oller.
The period of energization of the solenoid may be
expressed by the formula
p~ ~ = PWo ~ PWbv + PWACT
~ Where PWe is actual period of energization ,
' PW is a basic period of energization
o
PWbv is battery voltage compensation ,,
. ~ period
~ ~ PWAcT is actuator rod position compensa- -
tion period
Typlcally~PWO is the period of energization at no-
load on the`engine and may~be of the order of 12 to 15 milli-
" ~seconds,~and the~maximum increase ln response to the actua-
tlon~rod~position~may be~5~to~10 ml11i-seconds, the increase
belng~linear;over~the range of movement of the actuator rod.
The~increase~in~energiza~tion~period~for decline in battery
voltàgè~may~;be of~the~;~o~rder of 0.~5~mi11i-seconds per~volt.
~The~increase~of 5 to 10 mi11i-seconds~ for actuation rod
;~ ~ posltion~ls~fo~r ful]-~fuel~llng~under transient~load condition --
~30 ~and~is~considerably~greater~ of the order of 50%) than that
~ ~ requi~red~under~fu;ll--open-throttle~steady conditions. The
`~ ~ total time~p'er cyclé~that the~solenoid may be energised is
of cour,s~e;'l'imi~ted~by~the~;cycle time of the engine and the
tim~`required~t~o~fi~ the~met~ering chamber wlth fuel, the
35~ ;1atter~be~i;ng~of~the~order~of~8 milli-seconds.
It~is~des'irable from~combustion efficiency consi-
`'`d~er~ion~for~'injection of the fuel to terminate at a fixedin'`th'e~engine cycle.~Acco~r~dlngly,~when the perlod oE
` ~337533
~ 13 -
energization of the solenoid is varied the termination point
of the energization remains fixed and the additional time
is obtained by advancing the initiation point of the ener-
gization. Figure 4 of the drawings shows a typical variation
in the duration of application of the air to the fuel being
delivered in relation to the output of the potentiometer that
is directly related to the quantity of fuel being delivered.
In the preceding description the period of
energization of the solenoid has made the variable in
response to variations in metered quantities of fuel. How-
ever, it is to be understood that the purpose in varying
that period is to achieve a corresponding variation in the
mass of air available to effect the delivery of the metered
quantity of fuel. As the pressure of the air supply is
maintained constant by suitable pressure regulators, and in
practical terms temperature variations normally encountered
do not significantly influence the density of the air, the
mass of air delivered to the metering chamber is directly
related to the period that the air is available via the
; 20 solenoid valve 150.
~ When the englne is under transient conditions,
requiring a~rapid increase in fuelling, it can be difficult
to control-~a fuel metering and injection system to deliver
thè optimum amount of fuel. From commencement of a transient
the~first~one or two cycles of each cylinder should prefer-
ably~havs~a higher~fuel loadlng than when operating at the
same~throttle openlng~fo~r ste~ady state operation. This immed-
`~ iate~enrichment~of~the fuel mixture is required to give the
engine an acceptable rapid response when the throttle is
suddenly~opened~. It has now been found that an acceptabletrans~ient~resp~onse can be obtained from an engine utilizing
the~f`uel~me~tering~system~described above by increasing the
ma;s~s;:of~the;~a~ir~availa~ble to deliver the fuel that is not :`
~`dependent~on~any~ increase in~the metered quantity of fuel.
35~ During~op~eration of an engine, the internal
surfaces~of~the~fu~el delivery path, comprising delivery
condult~108~ and~associated injector nozzle 18, remain wetted
12~7~ii3;~
- 14 -
by the ~uel after each delivery of fuel and air through the
nozzle 18 to the engine. During substantially smooth engine
operation (i.e. steady state or light acceleration or decele-
ration) this residual wetting of the internal surfaces has
no significant effect on the operation of the engine, as the
amount of fuel retained by the wet surfaces remains substan-
tially constant while the amount of air used for each
delivery is constant.
Figure 5a illustrates the desired sequential fuel
deliveries from the nozzle 18, for an engine transient
requiring an immediate increase in fuel rate between deliver-
ies 5 and 6. Figure 5b shows typical delivered fuel quanti-
ties where the fuel metering and injection system is arranged
so that each of the twelve deliveries of fuel are propelled
by the same mass of air. The degree of residual wetting of
delivery line 108 is increased for increased metered quanti-
ties of fuel, and the amount of fuel delivered from the
injector nozzle is seen to increase gradually between
deliveries 5 and 9. From the first delivery at the new fuel
metering rate, the amount of fuel delivered from nozzle 18
would be less than the metered quantity determined at the
` position of the metering rod 115 in the metering chamber 1~0,
bècause the mass of air available cannot immediately handle
the~increased quantity of fuel, and there is an increase in
the residual wetness on the internal surfaces. However, the
amount of fuel retained wettlng delivery line 108 is a func-
tlon~both~of the ~quantlty~of fuel metered at the metering
chamber,~and of the mass of the air used to deliver the
- metered fuel along the conduit and out of the nozzle.
~Consider now Figure 5c where each delivery is
~ derived~from the same metered quantity~of fuel being in the
`~ ~ metering chamber~l~20.~However, the mass of air for delivery
6~has~been made larger than the others, by energizing the
s`olenoi~d~for a longer period. Delivery 6 ejects more fuel
3~5`~ from~the~nozzl~e 18 than de~livery 5, as it has reduced the
quantity~of fuel wetting the inner surfaces o delivery line
; 108~ Furth~er, de~livery 7~passes correspondingly less fuel
~ : .
.
. - . : , ~ .. . :
.. .. : . . . :, . :: . .:
.,- , . . . .
.. -.. : , ~ . .. . ..
~ Z ~ 3
than delivery 5 as some fuel will be left in the delivery
line 108 rewetting the surfaces. Subsequently delivery using
the normal mass of air will deliver an amount of fuel from
the nozzle corresponding to the metered quantity available
in the metering chamber 120.
Referring now to Figure 5d, this illustrates a
repeat of the engine transient conditions of Figure 5a except
the system is now arranged so that the increased amount of
fuel is propelled by an increased mass of air. Delivery 6,
being the first delivery at the increased metered quantity
of fuel and mass of air, will leave the delivery line 108
slightly less wet than the preceding delivery 5, while
following pulses 7-8-9 etc., will maintain that reduced
degree of~wetting. The effect on delivered fuel quantities
can be seen in Figure 5d. The transient fuel enrichment is
evident.~It will be appreciated that this arrangement
~provides also the desirable fuel enleanment on deceleration
~translents~due to the delivery line 108 entering a stage of
lncreased residu~al~wetting. ~
~ T~he use of;the~capab;ility of reducing the wetness
of the;internal surface~;of~the~fuel delivery conduit is
prèferabl~y~in combination~with~the increase;in~metered
quantit~y;~of fuel as; represented by~Figure~Sd,~ particularly
when~the~e~ngine~ s~experienc~lng~a~severe transient condi-
tion~ H~owe~ver,~eithe~r~ca`pabili~ty may~be used individually
The~;ele~c~tronIc~c;ontroller~192; may~be ~arranged~to respond to
a~t~ranslent~condltlon~s~ensed~by a~factor other~than the~
actuator~r`od~pos~it~ion~in~order;t~o~imp~lement~operation of the~
wetnes~s~reducti~on`~capabi~l~ity~,~such`as~by sensing the~rate of~0 ~ change~of~the~thrott1e~positlon.~
t~wl~ll however~be~appreciated that the invention
de~scrlbed~ hereln~l~s~ not~restrlcte~d to the particular
appa~ratus~déscribed~ n~detail~above, but is applicable to
all~fuel meteri;ng~and/or~del~ivery~sys~tems utilizing a pulse
of gas:to-propel a~metered~:quantlty of fuel for delivery to
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The metered t~uantity of fuel will depend on engine
load, transient state, engine cylinder size, and selected
operating air/fuel ratio, and may typically range from a few
milligrams up to say 100 milligrams (or more) per injection.
Correspondingly, the preferred mass of air delivered to the
metering chamber per injection may vary over the range 2
milligrams to 10 ~or more) miliigrams per injection. An
approximate volumetric ratio of air to fuel measured at
S.T.P. is 50:1. Air supply pressures are regulated but
metering operation may be achieved typically using supply
pressures over the range 200kPa to 1000kPa (or even higher).
Practically, the minimum pressure is determined by the need
to operate valves, and to supply sufficient air mass, so
that 400kPa is a more usual value. Similarly, maximum
pressures tend to be determined according to the need for
simple and efficient supply sources. In an automotive
- application~a single~stage compressor would be desired,
effectively limiting maximum pressures to around 800kPa.
~ ~Under some engine operating~conditions it may be
desirable to lncre~ase the mass ~of alr per injection even
though there is no corresponding increase in fuel quantity.
One~such condition~may be~during start-up of the engine
particular~ly under cold start~conditions. The additional air
will contr~ibute to improved atomization, particularly when
25 the~e`nglne is cold~and~vaporlzation i5 not~assisted by the ~i
heat of the engine~
~ The~engine c~ondition in response to which the mass
of air~is~varied may be timed from start-up so the air mass
decreases~as the~time after start-up increases until the air~
30 ~mass;~fall;s~to~a predètermined;limit. ~If the engine condi-
tion is~temperature~, again the air mass will decrease as the
temperature increases until a predetermined limit is reached.
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