Note: Descriptions are shown in the official language in which they were submitted.
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1
PRESSURISING A GAS INJECTION TYPE FUEL
INJECTION SYSTEM
This invention relates to fuel injection systems of the two fluid type for
internal combustion engines. In such engines, metered quantities of fuel are
delivered to a combustion chamber of the engine entrained in a gas, typically
air, supplied from a pressurised gas source, typically a gas duct of a rail.
Such fuel injection systems, whilst not limited to, are particularly
applicable to engines for use in automotive and outboard marine and
recreational applications. In such engines, commercial and user considerations
require that the engine start-up period be relatively short under a wide range
of
conditions. For example, an engine may be employed for operation under
ambient and extreme ambient conditions and efficient engine operation is
important no matter the conditions. An important part of achieving a rapid
start-
up period in such engines is the ready availability of compressed gas at an
adequate pressure to assure effective fuel delivery as close to start-up as
possible. However, for cost and other considerations, it is not convenient to
provide a relatively large compressed air storage capacity, and in any event,
there is also the risk of loss of pressure due to leakage, particularly when
the
engine has been inoperative for a certain period.
Typically, a compressor driven by the engine is provided as the means for
supplying compressed gas to an engine having a fuel injection system of the
type above described. For both reasons of economy and energy efficiency, it is
customary to select the compressor capacity to closely match the air
consumption rate of the engine. Thus, under start-up conditions, there is
typically no reserve supply of air at the appropriate pressure for fuel
delivery and
the compressor, and thus the engine, must complete a number of cycles before
air at the required pressure is available to assist in the injection of fuel.
The above factors each contribute to lengthening of the period between
commencement of the start-up sequence of the engine and the availability of
air
at the required pressure to assist in the injection of fuel.
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PCT1AU97/00438
Received O l October 1998
It is known from US Patent No. 4936279 assigned to the Applicant to
provide a fuel injection system wherein fuel is injected through a selectively
openable injector nozzle directly into the combustion chamber of the engine by
way of gas from a pressurised gas system. However, when the engine is in
start-up mode, gases delivered from an engine combustion chamber are
allowed to pass through the injector nozzle into the gas supply system to
assist
in a more rapid pressurisation thereof.
However, as will be seen from Figure 1 which relates to the prior art, the
opening of the injector nozzle over several consecutive cycles without any
control may lead to a cycling of pressure in the gas supply system. More
specifically, the pressure in the rail of the gas supply system will cycle in
accordance with the pressure present in the various combustion chambers of a
multi-cylinder engine, each equipped with an injector nozzle which is opened
at
a set timing before top dead centre and closed at a different set timing
before or
after top dead centre. Thus, although pressurisation of the rail is achieved,
there
are phases of depressurisation thereof corresponding to periods when the
injector nozzle of a cylinder is opened whilst the cylinder pressure is less
than
that to which the rail or other gas system has been charged during a previous
charging or "pump-up" event. These periods of depressurisation cost time in
terms of establishing the required pressure in the gas system as time is lost
in
recharging the rail to the value at which the previous charging event had
taken it
before any incremental rise in rail pressure can be achieved.
It is therefore the object of the present invention to provide further
reductions in the period required to bring the gas supply system of a dual
fluid
fuel injection system up to a pressure which will enable satisfactory fuel
injection
thereby.
With this object in view, there is provided a method of operating an
internal combustion engine having a fuel injection system including at least
one
injector means to deliver fuel entrained in a gas directly to a combustion
chamber of the engine, and a gas supply system in communication with the
injector means to provide gas thereto, said method including rendering the
injector means of at least one combustion chamber open over subsequent
AMENDED SHEET - IPEA/AU
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PCT/.AU97/00~438
Received Ol October 1998
3
engine cylinder cycles during engine start-up when the pressure in said at
least
one combustion chamber of the engine is substantially the same as or higher
than the pressure in the gas supply system to deliver compressed gas from said
combustion chamber through the injector means to the gas supply system
Typically, the gas supply system will be pressurised for subsequent delivery
of
fuel directly into at least one combustion chamber of the engine.
More particularly, the at least one injector is opened when the pressure in
the at least one combustion chamber is substantially the same as or higher
than
the pressure in the gas supply system upon engine start-up and after a
preceding pump-up event in the pump-up sequence. It should be noted that in
certain circumstances, opening the injector to enable a reverse flow of gas
therethrough from the combustion chamber to the gas supply system may
include maintaining the injector open following a previous gas and/or fuel
delivery event thereby.
A pump-up sequence is made up of at least one event in which a nozzle
of the injector is held open allowing pressurised gas to pass from the
combustion chamber to the gas supply system during start-up of the engine.
Such an event is a "pump-up" event. As will be expanded upon further
hereinafter, in a multi-cylinder engine, a sequence of pump-up events may be
made up of a number of separate pump-up events sequentially effected in
different cylinders of the engine. Alternatively, the pump-up events may be
restricted to only one or a number of the total number of cylinders in the
multi-
cylinder engine.
Preferably, during a sequence of pump-up events the injector nozzle is
opened and closed at successively closer timings to the top dead centre
position of a piston reciprocating in the combustion chamber of the engine as
the number of engine cycles since start-up is incremented. That is, the method
involves opening the injector nozzle and holding it open over an angle of
engine revolution commencing at a certain angle before top dead centre and
ending at a certain different angle before or after top dead centre.
Preferably, the periods of opening of the injector nozzle end at a certain
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angle after top dead centre. Preferably, the period of opening of the injector
nozzle is successively reduced during a sequence of pump-up events.
In a single cylinder engine, the angle at which the injector nozzle is
opened is progressively reduced with consecutive cycles of the engine. As
alluded to hereinbefore, in a multi-cylinder engine having a preset firing
order,
each cylinder in the firing sequence may have its injector nozzle opened over
a
lesser angle than that in a preceding cylinder in the pump-up sequence. In
this
manner, gas at successively higher pressure is introduced to the gas supply
system of the engine which, for example, may be an air duct of an engine rail
unit. Moreover, this can be done with economy in terms of the number of cycles
of engine operation required to bring the gas supply system up to the
requisite
pressure. In particular, the phenomenon is avoided whereby a depressurisation
phase takes place for each pump-up event prior to charging of the rail to a
successively higher pressure due to opening the injector nozzle too early or
closing it too late in a successive engine cylinder cycle. Hence, the timings
of
the pump-up events are optimised so that any loss of pressure from the gas
supply system is a minimum or is avoided altogether.
Conveniently, once the gas supply system has been charged up to a
level where gas assisted fuel injection can occur and the engine has
commenced firing, the injector nozzle may be held open for a certain period
after a metered quantity of fuel has been delivered by the injector to
continue
pressurising the gas supply system during the start-up period of the engine
and
prior to the main source of compressed gas being able to adequately pressurise
the gas supply system. Preferably, the injector nozzle may be held open until
after ignition as occurred in the at least one combustion chamber. In this
regard,
following ignition, peak pressure in the combustion chamber rises rapidly as a
consequence of combustion phenomena causing a consequential rise in the
pressure of the gas supply system, and, more particularly, an air rail of the
engine. It is advantageous to make use of this "surge" in pressure to charge
the
rail until the main source of compressed gas can adequately pressurise the
rail.
This in itself comprises a further aspect of the invention.
Conveniently, where the gas supply system takes the form of a rail, the
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rail will be communicated through suitable ducting to the working chamber of a
gas compressor and as typically the gas is air, the compressor of most
interest is
an air compressor. The rail may be "pumped up" to the desired pressure to
achieve the desired degree of fuel atomisation, say 550 kPa, though this will
5 vary with ambient or other conditions, in accordance with the method as
above
described. However, to enhance the process, a one way valve may be placed at
a convenient location between the rail and the ducting communicating the rail
with the compressor to avoid pressurisation of this ducting and/or the working
chamber of the compressor during the start-up period. In such manner, the rail
may be pumped up to the required pressure more rapidly. That is, a proportion
of the pump-up sequence is not expended in pumping up the ducting between
the compressor and the rail before satisfactory fuel injection can take place.
In
certain circumstances, the volume of the ducting may be up to one third that
of
the rail.
Preferably, the one way valve is located at the point that the ducting
intersects the rail to minimise that volume which is to be pumped-up during
engine start-up.
Further, the one way valve may also serve to prevent or reduce leak
down of pressure from the gas supply system following cessation of engine
operation. In this manner, a subsequent pump-up sequence may not need to
comprise as many pump-up events as in the case where the gas supply system
contains substantially no gas pressure. Accordingly, some reduction in the
length of the pump-up sequence may be possible.
Conveniently, the engine temperature at a start-up may be input to the
electronic control system of the engine to further optimise the necessary pump-
up sequence. For example, it is known that at lower temperatures a greater
degree of fuel atomisation is necessary to achieve stable engine operation.
Accordingly, this may require a higher gas pressure for delivery of fuel and
hence the gas supply system will need to be pumped-up to this higher level
before satisfactory fuel injection can take place. The opposite may be true
for
higher temperatures at which a satisfactory degree of vaporisation is believed
to
occur in the combustion chamber due to the higher temperature therein. Hence,
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for different engine temperatures, it is convenient that the gas supply system
be
pumped-up to different pressure levels before efficient fuel injection can
commence. Accordingly, the pump-up sequence may be made dependent on
engine temperature. This additional parameter upon which a subsequent
pump-up sequence is determined may be used on the assumption that at start-
up of the engine, no or minimal pressure exists in the gas supply system.
Alternatively, as further described below, an estimation of the residual
pressure
in the gas supply system may be made based on a known or representative
leak-down rate of the gas supply system of the engine.
In this latter regard, typically following cessation of engine operation, any
residual gas in the gas supply system will typically leak to atmosphere. This
might occur via, for example, the air compressor of the dual fluid injection
system. Accordingly, if this leak down rate is profiled against time, an
estimate
of the remaining gas pressure in the gas supply system may be made by an
electronic control system of the engine and used to modify the pump-up
sequence on start-up. That is, a lesser number of pump-up events, for example,
may be used to achieve satisfactory pressurisation of the gas supply system.
In a further embodiment, the leak down rate may be profiled against
engine temperature allowing estimation of the residual gas pressure on the
basis of a known engine temperature on start-up.
The invention will be more readily understood from the following
description of a preferred embodiment thereof made with reference to the
drawings in which:
Figure 1 is a graph of pressure versus engine operating cycles from
engine start-up in accordance with a prior art method of engine operation;
Figure 2 is a schematic showing the control of an engine operated in
accordance with one embodiment of the present invention;
Figure 3 is a sectional view through a typical form of metering and injector
rail unit as used in an engine operated in accordance with one embodiment of
the present invention;
Figure 4 is a perspective view of the rail unit employed in Figures 2 and 3;
Figure 5 is a pressure trace for each cylinder of a three cylinder engine
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operated in accordance with an embodiment of the invention; and
Figure 6 is a graph of pressure versus engine operating cycles from
engine start-up for an engirye operated in accordance with one embodiment of
the present invention.
The overall operation of an engine operated in accordance with one
embodiment of the present invention wit! nov~r be described with reference to
Figure 2, which shows a mufti-cylinder engine 20 having an air intake system
22, an ignition means 24, a fuel pump 23, and a fuel reservoir 28. The engine
further includes an electric starter motor 25 energised by a battery 70 upon
operation of a starter switch 71. An air compressor 29 is driven by a belt 320
from
an engine crankshaft pulley 33a. Mounted in the cylinder head 40 of the engine
is a fuel and air rail unit 11.
Referring now to Figure 3, there is showni in detail the fuel and air rail
unit
11 comprising a fuel metering unit l0,and an air injector or a fuel injection
unit
15 72 for each cylinder of the mufti-cylinder engine 20, which in the present
embodiment is a three cylinder two-stroke engine. However, the invention is
equally applicable to single cylinder configurations and mufti-cylinder
engines
of any number of cylinders of either the twp or tour stroke type whether
reciprocating piston engine or other forms of engines including rotary engine.
20 The body 8 of the fuel and air rail unit 11 is an extruded component with a
longitudinally extending air duct 13 and a fuel supply duct 14.
At appropriate locations, as shown in Figure 4, there are provided
connectors and suitable ducts communicating the rail unit 11 with air and fuel
supplies: duct 49 communicating air duct 13 with the air compressor 29; duct
53
providing an air outlet which returns air to the air intake system 22; duct 52
communicating the fuel reservoir 28 and fuel supply duct 14; and duct 51
providing a fueG return passage and communicating fuel supply duct 14 with
fuel
reservoir 28. The air duct 13 communicates with a suitable air regulator 27
and
the duct 51 communicates with the fuel reservoir 28 via a suitable fuel
regulator
26.
The fuel metering unit 10 is commercially available and requires no
detailed description herein. Suitable ports are provided to~ allow fuel to
flow
CA 02259602 2005-04-05
through the rail unit 11 and a metering nozzle 21 is provided to deliver fuel
to
passage 120 and thence to fuel and air injector 12.
The injector 12 has a housing 30 with a cylindrical spigot 31 projecting
from a lower end thereof, the spigot 31 defining an injection port 32
communicating with the passage 120. The injection port 32 includes a solenoid
operated selectively operable poppet valve 34 operating in a manner similar to
that as described in US Patent No 4934329. As seen in Fig 2, energisation
of the solenoid in accordance with commands from an electronic control
unit (ECU) 100 opens the valve 34 to deliver a fuel-gas mixture to a
combustion
chamber 60 of the engine 20 and, in accordance with the control strategy of
the
present invention, admits pressurised gases from the combustion chamber 60
through the air injector 12 and ultimately into the air duct 13, to pressurise
it on
start-up as described in further detaiP hereinbelow. However, it is not
intended to
15 limit the valve construction to that as described above and other valves,
for
example, pintle valve constructions, could be employed.
Returning to Figure 2r the electranic control unit (ECU) '100 receives
signals from a crankshaft speed and position sensor 44, of suitable type known
in the art, via the lead 45 and from an air flow sensor 46 located in the air
intake
20 system 22 via the lead 47. The ECU 100, which may also receive signals
indicative of other engine operating conditions s uch as the engine
temperature
and ambient temperature (not shown), determines, from all input signals
received the quantity of fuel required to be delivered to each of the
cylinders of
the engine 20. Engine temperature sensing is important in an .embodiment of
25 the invention described below where sensing of engine andJor ambient
temperature may be employed in determination of the required pump-up
sequence. This general type of ECU is well known in the art of electronically
controlled fuel injection systems and will not be described here in further
detail.
Opening of each injector valve 34 is controlled by the ECU 100 via a
30 respective lead 101 in timed relation to the engine cycle to effect
delivery of fuel
from the injection port 32 to a combustion chamber 60 of the engine 20. By
virtue of the two fluid nature of the system, fuel is delivered to the
cylinder
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9
entrained in a gas. In this regard, it is important that the pressure of the
gas,
particularly air, employed to entrain the fuel and deliver it in the form of
an
atomised dispersion, is sufficiently high to create the desired degree of
atomisation.
The passage 120 is in constant communication with the air duct 13 via
the passage 80 as shown in Figure 3 and thus, under normal operation, is
maintained at a substantially steady air pressure. Upon energising of the
solenoid, the valve 34 is displaced downwardly to open the injection port 32
so
that a metered quantity of fuel is carried by air through the injection port
32 into
the combustion chamber 60 of a cylinder of the engine 20.
Typically, the air injector 12 is located within the cylinder head 40 of- the
engine, and is directly in communication with the combustion chamber 60
defined by the reciprocation of a piston 61 within the engine cylinder. As
above
described, when the injection port 32 is opened and the air supply available
via
the passage 80 is above the pressure in the engine cylinder, air will flow
from the
air duct 13 through the passage 80, passage 120 and, entrained with fuel,
injection port 32, into the engine combustion chamber 60. However, if the air
supply in the air duct i 3 of the rail unit 11 is not at a sufficiently high
pressure it
cannot effectively carry the fuel through the injection port 32 into the
combustion
chamber 60. In particular, insufficient pressure to effect the delivery of
fuel-air
mixtures to the combustion chamber 60 typically exist at start-up of the
engine,
particularly where there has been sufficient time since previous operation of
the
engine to enable leakage from the pressurised air supply system or rail unit
11:
In accordance with the present method, a signal is provided to the ECU
100 from the starter switch 71, via a lead 102, when the starter switch 71 is
operated to energise the starter motor 25. The ECU 100 is programmed so that,
upon receipt of this signal, the ECU 100 will not instruct the fuel metering
unit 10
to deliver fuel to the injector 12, but, having determined the position of the
crankshaft 33 via the position sensor 44 will energise the solenoid of
injector 12
to open the irijection port 32. The opening of 'the injection port 32 is timed
in
relation to the cycle of the cylinder of the engine 20, as sensed by the
crankshaft
position sensor 44 and passed to the ECU 1U0 by tha lead 45, so that the
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injection port 32 will be opened at a pre-determined point in the compression
stroke of the particular cylinder of the engine 20.
Thus with the injection port 32 open and the engine 20 being cranked as
part of the engine start-up sequence, the pressure in the cylinder will rise
to a
5 level sufficient to cause air to flow from the engine combustion chamber 60
through the open injection port 32 into the passage 80 and into the air duct
13.
Having regard to the displacement volume of the engine cylinder, compared
with the volume of the air duct 13, and of the air space in each of the
injectors 12
coupled thereto, the air pressure in the air duct 13 can be brought up to a
10 satisfactory operating pressure in a minimal number of engine cylinder
cycles.
However, it is desired to avoid a situation where the air duct 13
depressurises as a consequence of a delivery of air from a respective engine
cylinder to the air duct 13 being initiated and terminated at the same timings
for
each successive cylinder cycle of the multi-cylinder engine. When this occurs
there is an initial inflow of air to the air duct 13 and then a certain degree
of
outflow during each successive cylinder cycle of the engine. Hence, some
pressure accumulated in the previous cylinder cycle is lost upon opening of
injection port 32 as the pressure in the air duct 13 is higher than in
combustion
chamber 60 for an initial portion of the compression stroke. Thereafter, the
pumping work done by piston 61 serves to further pump-up the air duct 13.
Accordingly, the pressure in the air duct 13 may cycle as shown in Figure 1
over
a number of cylinder cycles from start-up until a satisfactory pressure is
achieved therein. Thus, a greater number of cylinder cycles are required to
bring the pressure in the air duct 73 to the required operating level.
Consequently, the time interval required from initiation of start-up to
attainment
of the required pressure level in the air duct 13 is prolonged, and hence the
effective time required for starting of the engine 20 is also prolonged.
Therefore, rather than the ECU 100 setting the same injection port
opening and closing times for each successive pump-up event, the injection
port
32 is opened an incremented period later than in the previous cycle and closed
at a correspondingly earlier time than in the previous cycle so that advantage
may be taken of the successively higher pressures in the later portion of the
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compression stroke and the earlier portion of the expansion stroke. The ECU
100 may increment the opening time and decrement the closing time of injection
port in a stepwise or any desired algorithmic manner to ensure opening and
closing of the injection port closer to the top dead centre position for each
successive pump-up event.
In this manner, the drop in pressure in the air duct 13 between successive
cylinder cycles may be reduced and an appropriately determined increase in
the pressure may be achieved in the air duct 13 with little or no drop in
pressure
therein between the successive pump-up events. In this regard, the benefit may
be seen from Figure 6 which shows a much smaller degree of fluctuation in
pressure than shown in Figure 1. Further, with the selection of appropriate
opening and closing times for the injection port 32, the pressure in the air
duct
13 may be made to successively increase with no pressure loss over successive
pump-up events.
In the case of a multi-cylinder engine, there are "n" combustion chambers
60 and "n" air injectors 12. The timings of opening of each air injection port
32
will be set so as to avoid the depressurisation phenomenon discussed above.
Put another way, the period or crank angle between the start of air (SOA)
event
and the end of air (EOA) event of the injectors 12 is reduced over successive
cylinder cycles of the engine as shown for a three cylinder engine in Figure
5. In
this case, the air duct 13 of the rail unit 11 is pumped up to a desired
pressure
level in a shorter time. The ECU 100 may readily be configured to calculate
suitable SOA and EOA timings for each cycle of the engine optionally in
accordance with sensed rail pressure.
Further, the pump-up sequence is preferably arranged to be in the same
order as the firing sequence, which for an n cylinder engine may be 1,2...n.
Thus, at start-up, after a maximum of 360° of rotation for the engine
to determine
the position of the crankshaft 33, the injection port 32 of cylinder 1 , for
example,
will have certain SOA and EOA timings determined therefor, then the SOA and
EOA timings for the air injection port 32 of cylinder 2 will be set somewhat
closer
together (closer to top dead centre (TDC) that is SOA is retarded and EOA
advanced) such as to provide a higher delivery pressure than that provided by
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12
cylinder 1, then the SOA and EOA timings for the injection port 32 of cylinder
3
will likewise be closer together to provide an even higher pressure and so on
up
to n cylinders of the engine. Should pump-up still be required when the engine
firing sequence returns to cylinder 1, the SOA and EOA timings will be
incrementally higher and lower respectively than cylinder n of the previous
firing
cycle.
SOA and EOA timings may be set in the time or crank angle domain but,
in any event, may be set having regard to factors such as engine operating
temperature and/or sensed pressure in the air duct 13. SOA and EOA for the air
injectors 12 will generally occur before and after the top dead centre (TDC)
position of the piston 61 reciprocating in the cylinder respectively.
In a further variant, it is possible to continue pumping-up the air duct 13
even after fuel has commenced being delivered to the engine 20 for
combustion. In particular it is possible for the injection port 32 to be held
open
following delivery of fuel to ensure that ignition occurs whilst the injection
port 32
is still open. This provides a means of further charging the air duct 13 as
pressure in the combustion chamber 60 will increase rapidly following onset of
ignition and hence an equally rapid increase of the pressure of the air duct
13 is
possible. However, it is desirable that the injection port 32 not be held open
for
a period longer than is necessary to quickly attain the pressure of at least
550
kPa in the air duct 13. If the injection port is held open longer than
necessary,
there is diminishing benefit, insofar as combustion gases will be able to
enter
the air duct 13 and this may cause problems in terms of carbon build up in the
fuel injection system. In a preferred embodiment, the EOA takes place within
10° of the ignition event to prevent or reduce such an occurrence.
Further, it is
preferred that such subsequent pump-up events are only performed until the
compressor 29 is able to supply air at the appropriate pressure to the air
duct
13. This, for example, would occur after about 8-14 engine cylinder cycles.
It will be appreciated from the above discussion made with reference to
Figure 2 that the air supply system constitutes a relatively large volume. The
volume is made up of the air duct 13, the working chamber of the air
compressor
29, the duct 49 communicating the working chamber of the air compressor 29
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13
with the air duct 13 of the rail unit 11 and, optionally, an additional
chamber
provided between the compressor 29 and the air duct 13 of the rail unit 11 to
provide capacity to absorb pressure pulses arising from the cyclic nature of
operation of the reciprocating compressor 29. As it is intended to reduce the
time required to pressurise the air duct 13 to the minimum possible, it is
convenient to provide a one-way valve 50 as shown in Figure 2 between the air
duct 13 and the duct 49 communicating the air duct 13 with the working
chamber of the compressor 29.
Conveniently, the one-way valve 50 is incorporated into the rail unit 11
and is located at the very end of the air duct 13 at the point at which it
joins the
duct 49. Hence, during start-up whilst the compressor 29 is unable to provide
air at the appropriate pressure to the air duct 13, the one-way valve 50
serves to
isolate the air duct 13 from the compressor 29 and the duct 49. This may
reduce
the volume that is required to be pumped up at start-up by up to one third in
some instances. Hence only the air duct 13 of the rail unit 11 and not the
remaining portion of the air supply system is required to be pressurised at
start-
up. In this way, the volume required to be pressurised is minimised and the
air
duct 13 more rapidly reaches the operating pressure of, for example,
approximately 550 kPa which is required for appropriate fuel injection at 20-
25°
C.
This reduction of the air supply system volume is only necessary during
the cranking regime whilst the compressor 29 is not doing any significant
work.
Once the air compressor 29 is generating a higher pressure than can be
achieved using the method as above described, the one-way valve 50 will be
biased into an open position by the pressure delivered by the compressor 29
overcoming a spring or like means associated therewith allowing air to flow
continuously into the air duct 13 from the working chamber of the compressor
29. The valve 50 may be of any desired type but is ideally to be simple in
construction. However, there is no reason why this valve could not be a
solenoid actuated valve with appropriate timing set by the ECU 100. The
provision of such a one way valve 50 reduces overall cranking time to the
extent
that the first fuel injection event may take place one third to one half
revolution of
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14
the engine earlier and this is commercially advantageous.
The provision of compensation for engine temperature may be provided
for in accordance with the present invention. For example, the required air
pressure for satisfactory operation of the engine 20 varies with temperature
such
that the higher the engine temperature the lower the pressure required for
appropriate operation of the engine 20. Without wishing to be bound by any
theory, it appears that at low engine temperatures, the cylinder walls are
cold
and provide a heat sink for fuel thus preventing the formation of the desired
atomised fuel-air dispersion within the cylinder for efficient combustion.
Conversely, when the engine temperature is sufficiently high, it is evident
that a
lower air pressure is sufficient to achieve satisfactory atomisation of the
fuel and
air. Therefore, it may be appropriate to have the pump-up strategy controlled
by
the ECU 100 in relation to some measure of engine temperature. For example,
the engine coolant temperature may be used as a measure of engine
temperature for this purpose. If a higher air pressure is required at start-
up, due
to the engine 20 being at an initially low temperature, extra pump-up events
can
be scheduled during the start-up period of the engine 20. In this way, the
required schedule of pump-up events is achieved for any operating temperature
encountered by the engine 20. Where the pump-up sequence is dependent on
engine temperature, it is preferably implemented on the basis that no or
minimal
pressure exists in the air duct 13. Alternatively, an assumption may be made
that a certain air pressure remains in air duct 13 as described below.
When the engine 20 is shut down, it is possible that presence from within
the air duct 13 may leak down at a certain rate. This leak down rate may, for
example, be dependent upon the construction of the compressor 29 used on the
engine 20. Accordingly, if this leak down rate is known and the time for which
the engine has been inoperative is known, an estimate of pressure of the air
remaining in air duct 13 may be made by ECU 100. This information may be
used to modify the pump-up sequence as appropriate during the next start-up
event. Taking this concept a step further, the leak down rate may be related
to
the engine cooling rate. Therefore, by sensing the engine temperature at start-
up, a certain leak down rate of air duct 13 may be assumed and used to modify
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the pump-up sequence required. For example, if a certain level of pressure is
known to remain in the air duct 13, then a reduced pump-up sequence and
hence a shorter time to pressurise the air duct 13 may be achieved.
Although the provision of the one way valve 50 is particularly applicable
5 to assist in reducing the overall pump-up time for the air duct 13, it is
possible for
the one way valve 50 to be used in a manner that permits a "Limp Home" mode
in the case where the compressor 29 of the engine 20 fails.
If the compressor 29 fails, the one way valve 50 will typically close due to
the action of the biasing means associated therewith. A pressure sensor
10 arranged, for example, in the ducting communicating the working chamber of
the compressor 29 with the air duct 13 of the rail, may flag a value
indicating
compressor failure. When this is flagged, the ECU 100 may revert to a mode of
operation in which at least one air injector 12 of the engine 20 is opened for
a
period of time after completion of the fuel delivery from the injection port
32
15 thereof to the combustion chamber 60. This will permit gas from the
combustion
chamber 60 to pass through the injection port 32 of the air injector 12 to
raise
the gas pressure in the air duct 13 to a sufficient value to effect fuel
delivery
during the next engine cylinder cycle. The injection port 32 may be held open
for a period after and continuous with the injection of the fuel into the
combustion chamber 60 to allow gas to pass into the passage 80 and effect a
required rise of gas pressure in the air duct 13.
In a multi-cylinder engine, one cylinder may alternatively be used solely
to provide pressurisation of the air duct 13 whilst the other cylinders may be
operated to compensate for the engine running with one less cylinder.
Alternatively, gas may be delivered from each cylinder of the engine by way of
the method described in the previous paragraph.
In some engines, for example, those operating on a V6 configuration,
there may be two rail units 11, one for each bank of cylinders. If the
compressor
29 fails, one rail unit 11 may be employed to act as a source of compressed
air
by using a method as above described. The other bank of cylinders would
operate normally or in a manner to compensate for the modified mode of
operation. In such a system, certain provisions would need to be made to
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16
enable the air duct 13 of the first rail unit 11 to provide pressurised air
for use by
the second rail unit 11. The closure of the one-way valve 50 in the first rail
unit
11 will prevent leakage of air from the air duct 13 into the air supply system
and
thus enable engine operation even following compressor failure. This may
constitute a still further aspect of the present invention.
It may also be possible to construct a diagnostic mode whereby, if air duct
13 fails to reach the required pressure after a number of pump-up events air
compressor failure is indicated and such a "Limp Home" mode as previously
described is activated.
Whatever the variants of the present method employed, the start-up
pump-up sequence above described may be terminated when, for example, a
pressure sensor in the air duct 13 or duct 49 indicates that the pressure in
the air
duct 13 is sufficient to enable efficient operation of the engine 20. When
this is
flagged, the pump-up sequence may be terminated.
Although the present invention is particularly applicable to automotive
outboard marine and recreational engines, where short start times are
extremely
important, it may also be incorporated in dual fluid fuel injection systems
for
other types of engines. The invention is applicable to engines operating on
either the two stroke cycle or the four stroke cycle.
Upon reading of the above disclosure, the person of ordinary skill in the
art may develop modifications for variations thereof. These modifications and
variations fall within the scope of the present invention.
