(12) United States Patent
`Hurley et al.
`
`111111
`
`1111111111111111111111111111111111111111111111111111111111111
`US006581572Bl
`
`(10) Patent No.:
`(45) Date of Patent:
`
`US 6,581,572 Bl
`Jun.24,2003
`
`11/1982 Stumpp eta!. ............. 123/478
`4,359,991 A
`1!1987 Matsuura eta!. ........... 123/492
`4,633,841 A
`4,932,371 A * 6/1990 Albertson et a!.
`.......... 123/403
`4,971,011 A
`11/1990 Nanyoshi et a!. ........... 123/436
`4,986,245 A
`1!1991 Nakaniwa et a!. .......... 123/492
`5,080,064 A * 1!1992 Buslepp et a!. ............. 123/399
`5,251,597 A * 10/1993 Smith et a!. ................ 123/585
`5,282,448 A * 2/1994 Reinke et a!.
`.............. 123/403
`5,372,110 A * 12/1994 Boverie et a!.
`............. 123/361
`5,540,205 A * 7/1996 Davis et a!.
`................ 123/486
`6,058,906 A * 5!2000 Yoshino
`..................... 123/295
`
`(54) ENGINE FUELLING RATE CONTROL
`
`(75)
`
`Inventors: Richard William Hurley, Glen
`Waverley (AU); Martin David Hughes,
`Wembley Downs (AU)
`
`(73) Assignee: Orbital Engine Company (Australia)
`Pty Limited, Balcatta (AU)
`
`( *) Notice:
`
`Subject to any disclaimer, the term of this
`patent is extended or adjusted under 35
`U.S.C. 154(b) by 0 days.
`
`(21) Appl. No.:
`
`09/147,479
`
`(22) PCT Filed:
`
`Jul. 10, 1997
`
`(86) PCTNo.:
`
`PCT/AU97/00442
`
`§ 371 (c)(l),
`(2), ( 4) Date:
`
`Jan. 7, 1999
`
`(87) PCT Pub. No.: W098/01660
`
`PCT Pub. Date: Jan. 15, 1998
`
`(30)
`
`Foreign Application Priority Data
`
`Jul. 10, 1996
`
`(AU) . ... ... ... .. ... ... ... ... ... .. ... ... ... ... ... PO 0949
`
`Int. Cl? ................................................ F02D 41/04
`(51)
`(52) U.S. Cl. ....................... 123/478; 701!104; 701/105;
`123/480
`(58) Field of Search ................................. 123/478, 480,
`123/486, 492, 493, 399, 361, 403; 701/102,
`104, 105
`
`(56)
`
`References Cited
`
`U.S. PATENT DOCUMENTS
`3,554,170 A * 1!1971 Schenk et a!.
`
`.. ... ... ... ... 123/305
`
`FOREIGN PATENT DOCUMENTS
`0413 432 A2 *
`EP
`EP
`0 279 375 B1
`0 511 701 A1 *
`EP
`2066513
`GB
`* cited by examiner
`
`2/1991
`5/1992
`11/1992
`7/1981
`
`. .......... F02D/41!14
`
`........... F02D/41!26
`
`Primary Examiner---Hieu T. Vo
`(74) Attorney, Agent, or Firm-Arent Fox Kintner Plotkin
`& Kahn, PLLC
`
`(57)
`
`ABSTRACT
`
`A method for controlling the fuelling rate for an internal
`combustion engine including: a) controlling the fuelling rate
`in a fuel led control mode whereby the fuelling rate is
`controlled as a function of the operator demand on the
`engine during at least a portion of low engine load operation;
`b) controlling the fuel rate in an air led control mode
`whereby the fuelling rate is controlled as a function of the air
`flow rate to the engine during at least a portion of medium(cid:173)
`to-high engine load operation; and c) providing a point of
`transition between the two control modes wherein each
`control mode provides substantially the same predetermined
`fuelling rate.
`
`18 Claims, 2 Drawing Sheets
`
`a.p.c.
`(actual)
`
`A
`I
`fuel-led ----r-- 1
`a·r led C
`1
`-
`E
`
`I
`I
`I
`I
`I
`I
`I
`I
`I
`I
`
`X
`I
`I
`I
`I
`I
`I
`I
`
`I ""8
`
`p
`
`total t.p.c.
`(delivered)
`
`BOSCH-DAIMLER EXHIBIT 1013
`
`Page 1 of 7
`
`

`

`U.S. Patent
`
`Jun.24,2003
`
`Sheet 1 of 2
`
`US 6,581,572 Bl
`
`Fig 1.
`
`a.p.c.
`(actual)
`
`fuel-led ~
`
`X
`I
`I
`I
`I
`I
`I
`I
`I
`
`....
`
`air-led C
`
`A
`I
`I
`I
`I
`I
`I
`I
`I
`I
`I
`I
`I
`I
`~B
`
`E
`
`p
`
`total f.p.c.
`{delivered)
`
`Page 2 of 7
`
`

`

`U.S. Patent
`
`Jun.24,2003
`
`Sheet 2 of 2
`
`US 6,581,572 Bl
`
`1
`
`Look up demand_FPC
`
`2
`
`3
`
`Look up censor air I fuel
`ratio using demand_FPC and ~------; Engine speed
`..._ ____ __.
`engine speed
`
`8
`
`Calculate censor_FPC by
`dividing measured air flow
`by censor air I fuel ratio
`
`Measured air flow
`
`9
`
`YES
`
`4
`
`5
`
`Total_FPC = demand_FPC
`
`Total_FPC = censor_FPC
`
`10
`
`YES
`
`11
`
`13
`
`Look up air_led_FPC using
`engine speed and measured
`air flow
`
`Engine speed
`
`Measured air flow
`
`14
`
`Total_FPC = air_led_FPC
`
`12
`
`NO
`
`7 Engine_fuelling_rate = total_FPC
`
`Fig. 2
`
`Page 3 of 7
`
`

`

`1
`ENGINE FUELLING RATE CONTROL
`
`US 6,581,572 Bl
`
`The present invention generally relates to the control of
`the fuelling rate of internal combustion engines, and in
`particular to engines in which fuelling level and air flow
`level may be controlled independently, for example where
`fuel is supplied via electronically controlled fuel injection.
`In this specification, reference will be made to fuel delivery
`per cycle (fpc) and air flow per cycle (ape). A reference to
`either ape or fpc may refer to the level of fuelling/air flow
`determined to be required for appropriate operation of the
`engine (the "demand" ape/fpc), or to the fuel/air actually
`delivered to the engine, or to any other measure of air flow
`or fuelling level as the context requires.
`In many internal combustion engines, such as carburettor
`fuelled four stroke engines, the relationship between air flow
`rate and fuelling rate is substantially monotonic. In these
`engines, each air flow rate value corresponds to a single
`fuelling rate value. Engines having this characteristic are
`able to operate under what is known as air led control. In air
`led control, an air flow rate is set by driver demand, and
`fuelling level is subsequently determined as a function of the
`air flow rate to the engine.
`It is however not-normally possible to use such control in
`internal combustion engines having an air flow/fuelling level
`characteristic which provides non-unique values of fuelling
`level for a given air flow. One example of an engine having
`such a characteristic is the applicant's fuel injected two
`stroke crankcase scavenged engine. In this engine, airflow to
`the engine actually decreases with initial increases in fuel(cid:173)
`ling level (or rate) before rising, as fuelling level increases
`further, to above the initial air flow rate. It can be seen that
`it is possible to obtain non-unique values for fuelling rate for
`a single air flow rate. Many variations providing non-unique
`values are possible. For example, initial increases in fuelling
`may correspond to substantially no change in airflow. It is
`therefore not generally possible to use air led control of the
`fuelling rate at low engine loads in such engines.
`The Applicant's Australian Patent Application No.
`34862/93, describes a method for controlling the fuelling
`rate of an internal combustion engine, in particular a fuel
`injected two stroke engine, where a fuelling rate, or
`"Demand_FPC" is initially determined and the required air
`flow rate, or "Demand_APC" is subsequently determined
`on the basis of the Demand_FPC value. This method of 45
`controlling the fuelling rate is referred to as fuelled control.
`The Demand_FPC is determined as a function of operator
`demand as measured, for example, by sensing the throttle
`pedal position and the engine speed. The Demand_FPC can
`then be determined by means of a look-up map provided
`within the engine management system plotting the
`Demand_FPC against the coordinates of pedal position and
`engine speed. This look-up map is known as the "pedal" map
`because the driver initiated fuelling level is assessed by
`determining the operator pedal position. The Demand_APC
`for the above determined Demand_FPC is then determined
`using a look-up map plotting Demand_APC against the
`coordinates of Demand_FPC and engine speed. The deter(cid:173)
`mined Demand_APC is then compared with the measured
`air supply rate to the engine, or Measured_APC, as mea(cid:173)
`sured by an air mass sensor and, if possible, the air mass flow
`rate adjusted to compensate for any difference between the
`two. The resultant air/fuel ratio of Demand_FPC against
`Demand_APC can also be compared with a censor air/fuel
`ratio which is preset on the basis of the engine load demand 65
`and engine speed. The censor air/fuel ratios are stored on a
`further look-up map and set predetermined minimum limits
`
`5
`
`10
`
`2
`to the air/fuel ratio that can be applied for the existing speed
`and load. These limits to the air/fuel ratio are set to prevent
`specific engine malfunctions such as engine misfire, and
`take into account catalyst and/or emission considerations. If
`it is determined that the air fuel ratio is too low (ie rich
`mixture), the fuel supply may be clipped to avoid delivery
`of such rich mixtures to the engine.
`Fuel led operation may be disadvantageous in certain
`situations. In certain types of fuelling systems, such as those
`using fuel injectors, fuelling level can be altered quickly and
`accurately, whilst variation of the air flow rate is generally
`less accurate, slower and more difficult to control, particu(cid:173)
`larly under transient conditions, making control of the air
`fuel ratio in the combustion chamber more difficult. Sup(cid:173)
`plying air and fuel at an accurate air fuel ratio is important
`15 for controlling combustion emissions. As such, it is prefer(cid:173)
`able to have the airflow being set by driver demand and then
`to control the fuelling level to give the required air fuel ratio,
`that is, air led control.
`Another advantage of using air led control at higher
`20 load/speed occurs at or near wide open throttle (WOT)
`conditions where air led control can be used to achieve
`maximum power output from the engine. In fuel led
`operation, calculation of maximum fuelling for a given
`engine speed is based on experimental calibration of test
`25 engine(s). The calibrated maximum fuelling would normally
`be set at slightly lower than the test results indicated to
`provide a margin of safety to ensure that an overly rich
`mixture was not obtained. However, in actual operation,
`airflow to the engine may be higher than the experimental
`30 data indicated, particularly under transient conditions. This
`may result in the air fuel ratio in the combustion chamber
`being less than that for which maximum power can be
`obtained. At wide open throttle, for example, air flow is at
`its maximum, but maximum fuelling corresponding to the
`35 air flow may not be supplied due to the calibrated maximum
`fuelling rates, reducing the power output of the engine.
`Whilst fuel led control is necessary for low engine
`loads/speeds, this may not be so for higher load/speed
`conditions. In certain engines, such as the applicant's two
`40 stroke direct injected crankcase scavenged engine, there is a
`substantially monotonically increasing relationship between
`the fuelling rate and the air flow rate at higher loads. Under
`these loads it is possible, and preferable as discussed above,
`to use air led control of the fuelling rate.
`The major difficulty that arises with such an arrangement
`is that there can be a discontinuity at the point of transition
`between the two control methods. The fuelling rate deter(cid:173)
`mined under fuelled control could be significantly different
`to the fuelling rate determined under air led control at the
`50 point where the engine management system transfers
`between the two fuelling rate control methods. This can
`cause a step change in the determined fuelling rate resulting
`in a step change in torque. Such sudden changes may be
`detrimental to engine control and are undesirable as they
`55 may result in jolting through the drive train of the vehicle
`producing, for example, an uncomfortable ride for the
`occupants of the vehicle.
`It is therefore an object of the present invention to
`provide an improved method of controlling the fuelling rate
`60 of an engine.
`With this in mind, the present invention provides a
`method of controlling the fuelling rate for an internal
`combustion engine including:
`(a) controlling the fuelling rate in a fuelled control mode
`whereby the fuelling rate is controlled as a function of the
`operator demand on the engine during at least a portion of
`low engine load operation;
`
`Page 4 of 7
`
`

`

`US 6,581,572 Bl
`
`3
`(b) controlling the fuelling rate in an air led control mode
`whereby the fuelling rate is controlled as a function of the
`air flow rate to the engine during at least a portion of
`medium to high engine load operation;
`(c) providing a point of transition between the two control 5
`modes whereat each control mode provides substantially
`the same predetermined fuelling rate.
`As the point of transition between the two control modes
`occurs when the fuelling rate determined by either control
`mode reaches substantially the same predetermined thresh- 10
`old fuelling rate, there can therefore be a smooth transition
`in the fuelling rate when transferring between the two
`control modes.
`The predetermined threshold-fuelling rate may be deter(cid:173)
`mined from a look up map depending on current engine 15
`speed, so that for a given engine speed the transition point
`will be at a fixed fuelling rate.
`As noted above, at low loads, the airflow rate cannot be
`used to determine the engine load because for a given
`airflow rate, there may not be a unique corresponding 20
`fuelling rate. Where the engine operation is controlled by an
`electronic control unit (ECU) it is not possible to provide a
`map whereby a fuelling rate can be looked up on the basis
`of a given air flow rate. In this situation, a fuelled control
`mode for the fuelling rate is more appropriate. At medium to 25
`high loads, where there is a substantially monotonically
`increasing airflow rate for increasing fuel flow rate, a unique
`fuelling rate is therefore available for any given airflow rate
`at these loads, and the fuelling level can be determined on
`the basis of the current airflow. An air led control mode for 30
`the fuelling rate is more appropriate in this situation.
`The predetermined threshold fuelling rate for transition
`between control modes is preferably set above fuelling
`levels where a single air flow rate can correspond to more
`than one fuelling level which occur at low loads. A margin
`of variation may be provided about this value to allow for
`any errors or system anomalies.
`The engine air intake may be provided with a secondary
`valve such as that described in the applicant's U.S. Pat. No.
`5,251,597, known commonly as a DAR-valve. The DAR(cid:173)
`valve is an electronically controlled air flow control valve
`which is provided additionally to the primary air flow
`control valve, and provides a separately controllable airflow
`to the engine. In the above-mentioned U.S. patent, there is
`described a system wherein the primary air flow control
`device is a butterfly valve controlled directly by operator
`movement of an accelerator pedal. The DAR-valve in this
`situation is able, under the control of the electronic control
`unit (ECU), to selectively add to the volume of air provided
`by the primary valve device. As such, total air flow to the
`engine is controlled by the ECU. The DAR-valve may be
`used to ensure that air flow in the air led region at the
`transition point is at such a level that correct fuelling is
`provided. At higher loads, where the majority of the bulk air
`is provided through the primary valve (usually a butterfly
`valve), the ability of the DAR-valve to control air flow is
`diminished. As such, it is preferable to preset the transition
`point such that DAR-valve is in its region of authority, that
`is, still being effective in controlling the air flow rate through
`the inlet manifold to the requisite degree that the air flow
`may be controlled if the air flow is different to that required
`for the fuelling rate obtained under fuel led control. This
`may therefore avoid a step jump in the fuelling rate at the
`point of transition.
`In other embodiments, the primary air flow control device
`may be electronically controlled, and this control can be
`used in a similar fashion to the above described DAR-valve
`
`4
`air flow control method. One benefit of the use of an
`electronically controlled primary air flow device is that there
`is no problem with the "region of authority" as the primary
`valve obviously has authority throughout the operating
`range of the engine.
`According to the present invention, a "demand" fuelling
`rate may initially be determined as a function of the load
`demand and the engine speed. The load demand may be
`determined as a function of operator pedal position. To this
`end, an electronic engine management system may be pro(cid:173)
`vided including a look-up map having the demand fuelling
`rate plotted against the coordinates of pedal position and
`engine speed. This map is referred to as the "pedal" map and
`provides the demand fuelling rate.
`A censored air/fuel ratio referred to above may be
`obtained from a further look-up map setting predetermined
`minimum limits to the air/fuel ratio as a function of the
`engine speed and demand fpc. A censor fuelling rate may
`then be determined by dividing the air flow to the engine,
`measured for example by an air flow meter, by the obtained
`censor air/fuel ratio. This censor fuelling rate may be
`compared with the demand fuelling rate obtained from the
`pedal map. If the demand fuelling rate is greater than the
`censor fuelling rate, then the total fuelling rate (or delivered
`fpc) value may be set as being equal to the censor fuelling
`rate. However, if the demand fuelling rate is less than the
`censor fuelling rate, then the total fuelling rate may be set as
`being equal to the demand fuelling rate. This process is
`known as censoring the fuelling rate.
`The total fuelling rate (following censoring) may then be
`compared with a predetermined threshold fuelling rate
`value. If the total fuelling rate is less than the threshold
`fuelling rate value, then the total fuelling rate obtained above
`may be selected as the actual-fuelling rate delivered to the
`engine. However, if the total fuelling rate is greater then the
`threshold fuelling rate value, then an air led fuelling rate
`35 value may be obtained from a further look-up map plotting
`air led fuelling rate against the coordinates of measured air
`flow rate and engine speed. The total fuelling rate may then
`be set as being equal to the determined air led fuelling rate
`and air led operation is commenced without a sudden shift
`40 in fuelling rate or overall torque.
`The shift from fuel to air led operation, or air to fuelled
`operation, requires a change in basic operation of the engine
`and electronic control unit. As such, it would be undesirable
`to allow rapid changes between modes of operation. Such
`45 rapid changes in mode of operation could result, for
`example, from continuous engine operation at around the
`transition point. One method of preventing such rapid
`changes would be to provide a delay following a change of
`mode before allowing a return change of mode, such a delay
`50 would only need to be very short (around half a second, for
`example) to obtain the desired results.
`A preferred method would be to set the transition point for
`transition from fuel led mode to air led mode at a greater
`fuelling level than the transition point for transition from air
`55 led mode to fuel led mode. This would mean that fuelling
`level would have to be reduced by a given amount from its
`value at the point of transition from fuelled to air led (which
`would only occur if fuelling level were increasing) before a
`subsequent transition from air led to fuel led operation
`60 would be possible.
`It will be convenient to further describe the invention by
`reference to the accompanying drawings which illustrate a
`preferred embodiment of the invention. Other arrangements
`of the invention are possible and consequently, the particu-
`65 larity of the accompanying drawings is not to be understood
`as superseding the generality of the preceding description of
`the invention.
`
`Page 5 of 7
`
`

`

`US 6,581,572 Bl
`
`5
`
`In the drawings:
`FIG. 1 is a graph showing a typical relationship between
`the fuelling rate and the airflow rate in a fuel injected two
`stroke crankcase scavenged internal combustion engine; and
`FIG. 2 is a flow chart showing the control strategy
`according to the present invention.
`Referring initially to FIG. 1, the graph shows a typical
`relationship of the fuelling rate, referred to as "total FPC"
`and the airflow rate, referred to as APC. Curve C shows the
`change in the airflow rate as a function of the increase in
`fuelling rate. At low engine loads, the airflow rate can
`initially decrease with increasing fuelling rate before sub(cid:173)
`sequently increasing in a monotonic fashion at higher engine
`loads. At such low engine loads, two fuelling rate values can
`therefore correspond to a single air flow rate. It should be 15
`noted that alternative graph plot shapes at low load other
`than the shape shown in FIG. 1 are possible. For example,
`the graph plot may be straight or even undulating at the low
`load end thereof. Therefore, fuelled control of the fuelling
`rate is required to the left of dotted line A Air led control of
`the fuelling rate can be utilised to the right of dotted line A
`because of the monotonic increase in the air flow rate against
`the fuelling rate. The transition point B on curve C between
`the fuel led and air led regions is determined as a fixed
`predetermined total fuelling rate. Once the fuelling level has
`reached this transition point B, the control system converts
`to air led and vice versa for descending fuelling rates.
`This predetermined total fuelling rate B is set so that it is
`above the region where more than one fuelling rate can
`correspond to a single air flow rate, being the region to the 30
`left of dotted line X. Some variation around the fixed
`predetermined total fuelling rate is allowed for error or any
`system anomaly.
`The predetermined total fuelling rate is also set such that
`a DAR valve controlling the bypass line in the inlet manifold 35
`of the engine can still effectively control the air flow through
`the inlet manifold such that control of the airflow if the
`airflow is above or below the required fuelled fuelling rate
`value is still possible. This will avoid any step jump in the
`fuelling rate as the transition occurs. The region of effective 40
`DAR valve control of the airflow to the left of dotted line E
`can be known as the region of authority of the DAR valve.
`FIG. 2 shows the control strategy according to the present
`invention. At step 1, a demand fuelling rate or "demand_
`FPC" is obtained from a pedal map plotting demand_FPC 45
`against the co-ordinates of engine speed and pedal position.
`At step 2, a censor air/fuel ratio can be obtained from a
`further look-up map. In step 2, this look-up map plots the
`censor air/fuel ratio as a function of the engine speed
`determined at step 8 and demand_FPC calculated at step 1.
`A censor fuelling rate or censor_FPC is then determined by
`dividing the actual air flow to the engine measured by for
`example an air flow meter with the obtained censor air/fuel
`ratio.
`At step 4, the demand_FPC is compared with the
`censor_FPC. If the demand_FPC is less than or equal to the
`censor_FPC, then a total fuelling rate or total_FPC is set as
`being equal to demand_FPC at step 5. If the demand_FPC
`is greater than the censor_FPC, then a total_FPC is set as
`being equal to the censor _FPC at step 10.
`At step 6, the censor_FPC is compared against a thresh(cid:173)
`old fuelling rate value, known as the "threshold_FPC" at
`which the transition between fuel led and air led control is
`set. If the censor_FPC is less than or equal to the threshold_
`FPC, then the total_FPC obtained previously will become
`the actual fuelling rate delivered to the engine as shown at
`step 7. However, if the censor_FPC is greater than the
`
`6
`threshold FPC, then an air led control map is referred to in
`step 11, the look-up map plotting the air led fuelling rate or
`"air led FPC" against the co-ordinates of engine speed
`obtained at step 13 and the measured air flow rate obtained
`5 at step 14. The total_FPC is then set at the air led FPC at
`step 12, this total_FPC being the actual fuelling rate deliv(cid:173)
`ered to the engine at step 7.
`As the fuelling rate is modified by censoring in fuel led
`mode, and modified by air flow control in air led mode, a
`10 step change in the fuelling rate at the transition between fuel
`led control and air led control is avoided. This system avoids
`the need for a transition period over which there is some
`interpolation of the fuelling values of air led control and fuel
`led control to provide a smooth transition.
`Although the present invention is described-with respect
`to a fuel injected two stroke engine, it is also envisaged that
`the present invention be applicable to other types of engines,
`in particular those having an air flow/fuel delivery charac(cid:173)
`teristic similar to that of FIG. 1. That is, having non-unique
`20 air flow rates for any given fuelling rate.
`The claims defining the invention are as follows:
`1. An electronic control unit (ECU) for controlling opera(cid:173)
`tion of an internal combustion engine over a range of
`operating conditions between low engine load operating
`25 conditions and high engine load operating conditions, the
`ECU programmed to:
`(a) provide for operation of said engine according to a fuel
`led control mode wherein fuelling rates for said engine
`are selected by said ECU as a function of operator
`demand and air flow to said engine is adjusted by said
`ECU according to said fuelling rate;
`(b) provide for operation of said engine according to an air
`led control mode wherein fuelling rates for said engine
`are selected by said ECU as a function air flow to the
`engine, said air flow adjusted in accordance with opera(cid:173)
`tor demand;
`(c) operate said engine in said fuelled mode during at
`least part of a low engine load portion of said range of
`operating conditions;
`(d) operate said engine in said air led mode during at least
`part of a medium to high engine load portion of said
`range of operating conditions;
`(e) provide at least one transition point between the two
`control modes such that at said transition point each
`control mode provides substantially the same predeter(cid:173)
`mined fuelling rate.
`2. An ECU according to claim 1 including said ECU
`determining a threshold fuelling rate as a function of engine
`50 speed so that, for a given engine speed, said transition
`between said control modes is at a fixed fuelling rate.
`3. A method according to claim 1 wherein said ECU
`provides a threshold fuelling rate for said transition between
`said control modes, said threshold being set above fuelling
`55 levels where a single air flow rate can correspond to more
`than one fuelling level at low engine load operation.
`4. A method according to claim 1 including said ECU
`determining a threshold fuelling rate as a function of engine
`speed so that, for a given engine speed, said transition
`60 between control modes is at a fixed fuelling rate and wherein
`the threshold fuelling rate is set above fuelling levels where
`a single air flow rate can correspond to more than one
`fuelling level at low engine load operation.
`5. An ECU according to claim 1 wherein said ECU
`65 determines load demand as a function of an operator pedal
`position, the demand fuelling rate being a function of the
`pedal position and the engine speed.
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`7
`6. An ECU according to any one of claims 1-4, wherein
`said ECU controls primary air flow to the engine by adjust(cid:173)
`ing an electronically controlled air flow device.
`7. An ECU according to any one of claims 1-4, wherein
`the engine further includes a DAR-valve for assisting in the 5
`control of the air flow rate into the engine, wherein said
`transition between said control modes is within a region of
`air flow control authority of the DAR-valve.
`8. An ECU according to any one of claims 1-4 said ECU:
`(a) determining a demand fuelling rate as a function of the 10
`load demand on the engine and the engine speed;
`(b) determining a censored air fuel ratio for setting
`predetermined minimum limits to the air fuel ratio as a
`function of the engine speed and demand fuelling rate;
`(c) determining a censor fuelling rate by dividing the
`actual measured air flow to the engine by the obtained
`censor air fuel ratio;
`(d) comparing the censor fuelling rate with the demand
`fuelling rate;
`(e) setting a total fuelling rate delivered to the engine as
`being equal to the censor fuelling rate if the demand
`fuelling rate is greater than censor fuelling rate; or
`setting a total fuelling rate delivered to the engine as
`being equal to the demand fuelling rate if the demand
`fuelling rate is less than the censor fuelling rate;
`(f) comparing the total fuelling rate with a predetermined
`threshold fuelling rate value;
`(g) selecting the total fuelling rate to be the actual fuelling
`rate to be delivered to the engine if the total fuelling 30
`rate is less than the threshold fuelling rate value; or
`obtaining an air led fuelling rate value as a function of
`the measure air flow rate and the engine speed if the
`total fuelling rate is greater than the threshold fuelling
`rate value, such that the actual fuelling rate to be 35
`delivered to the engine is equal to the determined air led
`fuelling rate.
`9. An ECU according to any one of claims 1-4, wherein
`the fuelling level for the transition from fuelled control to
`air led control is greater than the fuelling level for the 40
`transition from air led control to fuel led control.
`10. A method of controlling the fuelling rate for an
`internal combustion engine over a range of operating con(cid:173)
`ditions between low engine load operating conditions and
`high engine load operating conditions, the method includ- 45
`ing:
`(a) a fuel led control mode wherein fuelling rate is
`selected as a function of operator demand and air flow
`to said engine is adjusted according to said fuelling 50
`rate;
`(b) an air led control mode wherein fuelling rate is
`controlled as a function of air flow to the engine and
`wherein air flow to the engine is adjusted in accordance
`with operator demand;
`(c) operating said engine in said fuelled mode during at
`least part of a low engine load portion of said range of
`operating conditions;
`(d) operating said engine in said air led mode during at
`least part of a medium to high engine load portion of 60
`said range of operating conditions; and
`(e) providing at least one transition point between the two
`control modes such that at said transition point each
`control mode provides substantially the same predeter(cid:173)
`mined fuelling rate.
`
`8
`11. A method according to claim 10 including determining
`a threshold fuelling rate as a function of engine speed so that,
`for a given engine speed, said transition point between said
`control modes is at a fixed fuelling rate.
`12. A method according to claim 10 wherein a threshold
`fuelling rate is provided for said transition point between
`said control modes, said threshold being set above fuelling
`levels where a single air flow rate can correspond to more
`than one fuelling level at low engine load operation.
`13. A method according to claim 10 further including:
`determining a threshold fuelling rate as a function of
`engine speed so that, for a given engine speed, the
`transition point is at a fixed fuelling rate and wherein
`the threshold fuelling rate is set above fuelling levels
`where a single air flow rate can correspond to more than
`one fuelling level at low engine load operation.
`14. A method according to any one of claims 10-13
`wherein primary air flow to the engine is controlled by an
`20 electronically controlled air flow device.
`15. A method according to any one of claims 10-13,
`wherein the engine further includes a DAR-valve for assist(cid:173)
`ing in the control of the air flow rate into the engine, and
`wherein said transition between said control modes is within
`25 a region of air flow control authority of the DAR-valve.
`16. A method according to any one of claims 10-13
`wherein the fuelling level for the transition from fuel led
`control to air led control is greater than the fuelling level for
`the transition from air led control to fuel led control.
`17. A method according to any one of claims 10-13
`including:
`(a) determining a demand fuelling rate as a function of the
`load demand on the engine and the engine speed;
`(b) determining a censored air fuel ratio for setting
`predetermined minimum limits to the air fuel ratio as a
`function of the engine speed and demand fuelling rate;
`(c) determining a censor fuelling rate by dividing the
`actual measured air flow to the engine by the obtained
`censor air fuel ratio;
`(d) comparing the censor fuell