||||||||l|||||lllllllllllllllllllllll|||||lllll||ll||||||llllllllllllllllll
`USOOS479898A
`
`United States Patent
`
`[191
`
`Cullen et a1.
`
`[54]
`
`[75]
`
`[73]
`
`[21]
`
`[22]
`
`[51]
`[52]
`[58]
`
`[56]
`
`METHOD AND APPARATUS FOR
`CONTROLLING ENGINE TORQUE
`
`Inventors: Michael J. Cullen, Northville; Louis
`R. Christensen, Canton; Peter J.
`Grutter, Plymouth; Michael A.
`Weyburne, Northville, all of Mich.;
`Joseph N. Ulrey, Hiroshima, Japan;
`David G. Farmer, Plymouth, Mich.
`
`Assignee: Ford Motor Company, Dearbom,
`Mich.
`
`App]. No.2 270,963
`
`Filed:
`
`Jul. 5, 1994
`
`Int. Cl.6 ...................................................... F02D 41/00
`US. Cl.
`..............
`123/350; 364/431.07
`
`Field of Search ..................................... 123/350, 349,
`123/352, 361, 340; 73/1173; 477/110;
`364/426.04, 431.07; 60/277
`
`References Cited
`
`U.S. PATENT DOCUMENTS
`
`4,853,720
`5,078,109
`5,190,017
`5,241,855
`
`........................ 364/431.07
`8/1989 Onari et a1.
`l/1992 Yoshida et a1.
`.
`123/350
`3/1993 Cullen et a1.
`123/571
`9/1993 Cullen et a1.
`.......................... 73/1173
`
`[11] Patent Number:
`
`5,479,898
`
`
`[45] Date of Patent:
`Jan. 2, 1996
`
`5,333,109
`5,391,127
`
`
`7/1994 00 et a1. ............ 364/426.04
`2/1995 Nishimura ............................... 477/110
`
`Primary Examiner—Raymond A. Nelli
`Attomey, Agent, or Firm—Allan J. Lippa; Roger L. May
`
`[57]
`
`ABSTRACT
`
`A method for reducing the engine torque being produced by
`an internal combustion engine to a desired engine torque
`through coordinated control of spark retard, cylinder cut-out
`and air/fuel scheduling. The method is for use with a vehicle
`including a multi—cylinder
`internal combustion engine
`capable of generating torque, each cylinder having an asso-
`ciated fuel injector for providing fuel to the cylinder and an
`associated spark timing control for providing a spark for
`combustion of the fuel with fresh air during engine opera-
`tion. The method includes identifying the desired engine
`torque to which the engine torque being produced is to be
`reduced, and determining a first torque reduction to be
`achieved by defueling at least one of the engine cylinders.
`The method also includes determining a second torque
`reduction to be achieved by lean air/fuel scheduling, the
`second torque reduction being adjusted for the number of
`cylinders defueled, and determining a third torque reduction
`to be achieved by spark retardation, the third torque reduc-
`tion being adjusted for the number of cylinders defueled and
`for the lean air/fuel scheduling.
`
`17 Claims, 6 Drawing Sheets
`
`
`
`14
`
`OPERATING
`PARAMETERS
`
`1of12
`
`FORD 1888
`
`1 of 12
`
`FORD 1888
`
`

`

`US. Patent
`
`Jan. 2, 1996
`
`Sheet _1 of 6
`
`5,479,898
`
`16
`
`14
`
`
`
`OPERATING
`PARAMETERS
`
`
`
`
`2W 1
`1
`1o /
`
`.
`
`30
`
`34
`
`38
`
`VEHICLE SPEED
`TORQUE LIMIT
`
`TRANSMISSION ‘
`TORQUE LIMIT
`
`32
`
`36
`
`ENGINE SPEED
`TORQUE LIMIT
`
`TIP-IN
`TORQUE LIMIT
`
`
`
`TQ_LIM_RPM TO_L|M_TRANS
`
`TO_LIM_VS
`
`TO_L|M__TI P
`
`TQJJMJRAC‘
`
`
`TRACTION CONTROL
`TORQUE LIMIT
`
`
`
`
`
`40
`
`TIP-OUT
`TORQUE LIMIT
`
`-
`
`TO_LIM_DP
`
`42 _ ‘lW
`TO_MAX_ALLOW
`!
`
`LOWEST NET ENGINE TORQUE
`
`<
`
`CATALYST
`TEMPERATURE
`
`48
`
`45
`
`4"
`
`TORQUE
`CALCULATIONS
`
`EXT—0M0
`
`'
`' TORQUE
`
`TO MBT
`-
`
`CONTROL MODULE —mLOSS
`
`I
`
`-
`
`55
`
`50
`
`r—L _’'
`52
`|NJ_0N
`54
`
`OPEN
`LOOP FUEL
`
`,
`
`FUEL
`CUT-OUT
`
`SPARK
`ADVANCE
`
`ACTUAL
`TORQUE
`CALCULATIONS
`
`.
`'
`TRCLNET TQ_|MP
`
`we
`
`2 of 12
`
`FORD 1888
`
`2 of 12
`
`FORD 1888
`
`

`

`US. Patent
`
`Jan. 2, 1996
`
`Sheet 2 of 6
`
`5,479,898
`
`'
`W 5’4
`
`START
`
`60
`
`
`
`EXT_CMD
`CALMEXLEAN
`
`
`
`N
`
`62
`
`I
`
`W
`66
`
`
`
`TORQUE
`REDUCTION
`RECIUESTED
`
`
`
`SET CATALYST
`OVERTEMP FLAG
`
`
`
`N
`
`as
`
`EXT__FLG__LEAN = o
`
`N
`
`g Y
`
`74
`
`N
`
`N
`
`70
`
`72
`
`A
`
`F
`
`
`A/
`AT RICH
`LIMIT
`
`
`
`
`ASSIGN MINIMUM
`
`
`DISALLOW SPARK
`
`TORQUE RATIO
`'
`RETARD; CUT-OFF
`ATTAINABLE BY
`
`
`FUEL INJECTORS
`
`SPARK RETARD
`
`
`
`78
`
`3 Of12
`
`'
`
`FORD 1888
`
`3 of 12
`
`FORD 1888
`
`

`

`US. Patent
`
`Jan. 2, 1996
`
`Sheet 3 of 6
`
`5,479,898
`
`em 5%
`
`tr_des = (T0_MAX_ALLOW
`+ T0_LOSS) ITO_MBT
`30
`.
`
`82
`
` tr_des >
`TR_SPK_LVL +
`
`TR_SP|§_LVL_H
`
`86
`
`
`
`
`
`
`
`‘
`1
`
`SPK_TQ_RATIO =
`tr_des/
`FUNC623(DES_LAMBSE)
`
`94
`
`96
`
`
`
`tr_inj_tq =
`tr__exst / TR_LAM__M|N
`
`
`tr_des * NUMCYL
`
`98
`
`4 of 12
`
`FORD 1888
`
`4 of 12
`
`FORD 1888
`
`

`

`U.S. Patent
`
`Jan. 2, 1996
`
`Sheet 4 of 6
`
`5,479,898
`
`100
`
`INJON = min(INJON_MAX, tr_inj_trq)
`
`102
`
`104
`
`TR_AF = tr_des/l NJ_TR/tr_exst
`
`106
`
`LAM_TQ = FUN0632(TR_AF)
`
`DES_LAMSE = MIN(LAM__TQ, FNMAXLAM(N, LOAD)
`
`
`
`
`
`
`108
`5—.9
`
`110
`
`g?“ 3t
`
`.
`
`1.0
`
`0.9J_l_J_LLLJ__|_L..
`
`0.8
`
`0.7
`
`0.6
`
`T0_SPKLVL
`
`0
`
`.
`
`0
`
`1
`
`5 of 12
`
`END
`
`‘
`
`fig 4
`
`2
`
`3
`
`4
`
`5
`
`6
`
`TQ__SOURCE
`
`FORD 1888
`
`5 of 12
`
`FORD 1888
`
`

`

`US. Patent
`
`Jan. 2, 1996
`
`Sheet 5 of 6
`
`5,479,898
`
`
`
`
`
`Ind.T0/lnd.TQ@14.6A/F
`
`1.05
`
`_s
`
`0.95
`
`0.85
`
`0.9
`
`0.8
`
`NF
`
`3&5
`
`20
`
`19
`
`18
`
`17
`
`16
`
`15
`
`14
`
`13
`
`12
`
`11
`
`10
`
`NFrequired
`
`0.8
`
`0.85
`
`0.9
`
`0.95
`
`1
`
`1 .05
`
`Desired ltq/Itq@14.6
`
`52¢ 6
`
`6 of 12
`
`.
`
`FORD 1888
`
`6 of 12
`
`FORD 1888
`
`

`

`US. Patent
`
`Jan. 2, 1996
`
`Sheet 6 of 6
`
`5,479,898
`
`
`
`Q '
`
`2a:
`
`Cl
`
`—
`
`0
`
`5
`
`10
`
`15
`
`20
`
`25
`
`30
`
`35
`
`DEG. BTDC
`IGNITION TIMING
`
`W 7
`
`= 600 RPM
`
`= 1000 RPM
`
`= 2000 RPM
`
`= 3000 RPM
`
`<IOUI>
`
`7 of 12
`
`FORD 1888
`
`7 of 12
`
`FORD 1888
`
`

`

`1
`METHOD AND APPARATUS FOR
`CONTROLLING ENGINE TORQUE
`
`TECHNICAL FIELD
`
`The present invention relates to a method and apparatus
`for controlling internal combustion engine torque to a
`desired torque value during vehicle operation.
`BACKGROUND ART
`
`Generally, it is desirable to be able to control internal
`combustion engine torque during vehicle operation. Various
`reasons exist for reducing the amount 'of engine (brake)
`torque generated. For example, there may be a need for a
`reduction of engine torque for traction control or anti-spin
`control purposes. Furthermore, engine torque may need to
`be reduced in order to protect certain vehicle components.
`In addition to being able to determine how much engine
`torque should be reduced, it is also desirable to identify and
`implement the appropriate control actions required to reduce
`the torque to the desired torque in an acceptable period of
`time. For example, controlling the amount of air delivered to
`the engine for combustion purposes is generally a slower
`process than controlling spark advance. Although existing
`strategies have utilized spark retard and/or cylinder cutoff to
`reduce torque, the prior art has yet to teach the coordinated
`control of the present invention.
`There is,
`therefore, a need to develop a strategy for
`controlling the amount of net engine torque produced by an
`internal combustion engine utilizing coordinated torque
`reduction control operations.
`\
`
`SUMMARY OF THE INVENTION
`
`It is an object of the present invention to provide a method
`and system for controlling the amount of engine torque
`produced by an internal combustion engine through coordi—
`nated management of various control actions.
`In carrying out the above object and other objects and
`features of the present invention, there is provided a method,
`for use with a vehicle including a multi-cylinder internal
`combustion engine capable of generating torque, each cyl—
`inder having an associated fuel injector for providing fuel to
`the cylinder and an associated spark plug for providing a
`spark for combustion of the fuel with fresh air during engine
`operation, for reducing the engine torque being produced to
`a desired engine torque. The method comprises identifying
`the desired engine torque to which the engine torque being
`produced is to be reduced, and determining a first torque
`reduction to be achieved by defueling at least one of the
`engine cylinders. The method also comprises determining a
`second torque reduction to be achieved by lean air/fuel
`scheduling, the second torque reduction being adjusted for
`the number of cylinders defueled, and determining a third
`torque reduction to be achieved by spark retard, the third
`torque reduction being adjusted for the number of cylinders
`defueled and for the lean air/fuel scheduling,
`the first,
`second and third torque reductions being implemented so as
`to reduce the engine torque being produced to the desired
`engine torque.
`A system is also provided for carrying out the method.
`The advantages accruing to the present invention are
`numerous. For example, various control operations are
`closely coordinated to obtain a desired engine torque, with
`little calibration efiort due to the algorithmic nature of
`strategy. The strategy implements control operations for
`quick and significant reductions in torque, and control
`
`5,479,898
`
`2
`
`operations for producing a continuum of smaller torque
`changes between large torque changes resulting from the
`quick and significant reductions in torque. The result is
`smooth torque transitions which enhance customer satisfac-
`tion and driveability.
`The above object and other objects, features, and advan-
`tages of the present invention will be readily appreciated by
`one of ordinary skill in the art from the following detailed
`description of the best mode for carrying out the invention
`when taken in connection with the accompanying drawings.
`BRIEF DESCRIPTION OF THE DRAW]NGS
`
`FIG. 1 is a block diagram representation of a system for
`controlling engine torque according to the present invention;
`FIG. 2 is a block diagram illustrating the relationship
`between the various modules of the torque control strategy
`of the present invention;
`FIGS. 3a—3c are a flowchart detailing the methodology
`for torque control according to the present invention;
`FIG. 4 is a graphical
`illustration of the relationship
`between a desired minimum torque ratio due to spark retard
`and the source of the torque reduction request;
`FIG. 5 is a graphical representation of the function which
`relates spark ofiset from MBT to a torque ratio;
`FIG. 6 is a graphical representation of a function which
`relates the lean A/F required to achieve a given desired
`torque ratio;
`FIG. 7 is a graphical representation of a function which
`relates the effect of NF on indicated torque; and
`FIG. 8 is a graphical representation of a function which
`relates NP and engine load for use with the present inven-
`tion.
`
`BEST MODE FOR CARRYING OUT THE
`INVENTION
`
`Referring now to FIG. 1, there is shown a block diagram
`representation of a vehicle system, shown generally by
`reference numeral 10, including an electronic control unit
`(ECU) 12 including a microprocessor for controlling a
`spark—ignited internal combustion engine 14. The engine 14
`includes well-known fresh air intake 16 hardware, a plurality
`of fuel injectors shown generally by reference numeral 18,
`and a plurality of spark plugs shown generally by reference
`numeral 20. Preferably, the system operates according to the
`present invention to control the net engine torque produced
`by the engine 14 to a desired torque.
`As is known, the microprocessor has both volatile and
`non-volatile memories, such as a keep-alive memory and
`ROM, associated therewith. The ECU 12 could also include
`additional memories separate from and external
`to the
`microprocessor. During vehicle operation, the microproces-
`sor executes
`software typically stored in non-volatile
`memory, continually gathering in a real-time fashion a
`plurality of both vehicle and engine operating parameters
`from well—known sensors (not specifically illustrated for the
`sake of clarity) for purposes of vehicle and engine control.
`These parameters include, but are not limited to, mass air
`flow, engine speed, coolant temperature, exhaust gas oxy-
`gen, vehicle speed, and throttle position.
`Utilizing the sensed data, the microprocessor controls
`various aspects of both vehicle and engine operation. As
`shown, the microprocessor controls the air/fuel (A/F) sched-
`uling, the fuel delivery, and the spark advance. For A/F
`scheduling, the microprocessor controls the amount of fresh
`air delivered to the individual cylinders of the engine 14. For
`
`5
`
`10
`
`15
`
`20
`
`25
`
`30
`
`35
`
`4o
`
`45
`
`50
`
`55
`
`60
`
`65
`
`8of12
`
`FORD 1888
`
`8 of 12
`
`FORD 1888
`
`

`

`5,479,898
`
`3
`fuel delivery, the microprocessor controls the plurality of
`engine fuel injectors through a like plurality of standard fuel
`injector driver circuits. The associated fuel injectors provide
`fuel to the combustion cylinders in terms of a pulse width
`determined by the microprocessor based on the operating
`parameters. For spark,
`the microprocessor controls the
`amount of spark retard/advance.
`
`there are various
`According to the present invention,
`requesters for reducing the current engine or brake torque,
`the lowest of which is granted and becomes the desired
`engine torque. The desired engine torque is preferably
`converted into an indicated torque (i.e. brake torque plus
`friction torque) by adding in the torque losses and then
`determining a ratio of desired indicated torque over current
`indicated torque. This ratio is then used to determine the
`appropriate control action.
`The preferred embodiment utilizes three control opera-
`tions to eifect a torque reduction. These operations are spark
`retard, A/F scheduling, and fuel injector cutout. Generally,
`smaller torque reduction requests are handled by spark
`retard. For larger reduction requests, a particular control
`priority, such as one of injector cutout, AIF scheduling, and
`spark retard may be implemented.
`When the inferred catalyst temperature indicates an over—
`temperature condition (e.g. such as during a torque reduction
`event), spark retard is precluded as a possible control
`operation by the torque control strategy, due to the relation-
`ship between retarding of spark and temperature. Further-
`more, a minimum number of cylinders may be disabled for
`cooling purposes if one of the appropriate conditions are
`met: e.g., if the NF is lean (some cylinders 011), and the
`catalyst midbed temperature is above the lean maximum
`midbed temperature, or if the AIF is rich/stoic (cylinders are
`on) the AIF controller is at its rich limit, and the catalyst
`midbed temperature is above the rich maximum midbed
`temperature.
`
`Referring now to FIG. 2, there is shown a block diagram
`for torque control according to the present invention. As
`previously noted, there may be various reasons to limit
`current brake torque. As such,
`the ECU 12 implements
`various brake torque reducing requesters, such as a vehicle
`speed torque limit (VSTL) 30, an engine speed torque limit
`(ESTL) 32, a transmission torque limit (TTL) 34, a tip-in
`torque limit (TITL) 36, a traction control
`torque limit
`(TCTL) 38, and a tip-out torque limit (TOTL) 40. The VSTL
`30 and ESTL 32 function to limit vehicle speed and engine
`speed, respectively. The Tl‘L operates to prevent damage to
`the transmission, and the TCTL operates in conjunction with
`a traction control strategy to control the relative slip between
`the vehicle wheels and the road surface. The TITL and
`
`TOTL limit the rate of torque increase and/or decrease
`during tip-in and tip—out so as to reduce powertrain windup
`and impact caused by drivetrain lash.
`With continuing reference to FIG. 2, block 42 determines
`the lowest requested net engine torque based on the various
`maximum net engine torques allowed by vehicle speed
`limiting, engine speed limiting, tip-in and tip-out torque
`control, traction control and transmission strategy described
`above, as well as the maximum net torque that could be
`produced by the engine (TQ_NET_MBT), which is gen-
`erated by block 44. Generally, the lowest net torque calcu-
`lation performs comparisons between the various maximum
`net engine torques to obtain the lowest torque requested. The
`various torque reduction requesters and the lowest torque
`calculation block 42 are also described in U.S. patent
`application Ser. No. 08/057,920, filed on May 7, 1993, titled
`
`10
`
`15
`
`20
`
`25
`
`30
`
`35
`
`40
`
`45
`
`50
`
`55
`
`60
`
`65
`
`4
`“Torque Managed Traction Control for the Drive Wheels of
`an Automotive Vehicle”, assigned to the assignee of the
`present
`invention,
`the specification of which is hereby
`expressly incorporated by reference in its entirety.
`As best shown in FIG. 2, the output of block 42 is the
`maximum torque allowable (TQ_MAX_ALLOW), which
`is provided to a torque control module block 46. The torque
`control module block 46 also receives as input a signed
`inferred catalyst midbed temperature (EXTMCMD) from a
`catalyst
`temperature model block 48, TQ_MBT, and
`TQ_LOSS from block 44.
`A detailed description of the determination of the catalyst
`midbed temperature can be found in U.S. Pat. No. 5,190,
`017, and U.S. patent application Ser. No. 08/196,735, filed
`on Feb. 15, 1994, titled “Method and Apparatus To Limit A
`Midbed Temperature of a Catalytic Converter”, both of
`which are assigned to the assignee of the present invention,
`the specifications of which are hereby expressly incorpo-
`rated by reference in their entirety. Generally, block 44
`calculates the maximum brake torque available at the engine
`output at a stoichiometric A/F ratio utilizing a base torque
`value modified for accessory loads and engine friction. A
`detailed description of the determination of TQwMBT and
`TQ_LOSS can be found in U.S. Pat. No. 5,241,855, titled
`“Method and Apparatus for Inferring Engine Torque”,
`assigned to the assignee of the present invention, the speci-
`fication of which is hereby expressly incorporated by refer-
`ence in its entirety.
`As shown in FIG. 2, the outputs of torque control module
`46, LAM_TQ (AIF ratio), INJ~ON (the number of fuel
`injectors to be energized), and SPK_TQ‘_RATIO (the
`torque ratio to be obtained by retarding spark) are generated '
`and utilized for torque control via an open loop fuel control
`action at block 50, a fuel cut-out control action at block 52,
`and a spark advance control action at block 54 as described
`in greater detail hereinbelow.
`Referring now to FIGS. 3a-3c, there is shown a flowchart
`detailing the steps for torque control according to the present
`invention. At step 60 of FIG. 3a, the ECU 12 compares the
`catalyst midbed temperature to CAT_MAXLEAN, the vari-
`able representing the catalyst midbed temperature limit for
`prohibiting torque control spark retard reductions during
`lean A/F scheduling. If there is a midbed over-temperature,
`at step 62 the ECU determines whether the NF is lean, such
`as based on the value of DES_LAMBSE, the desired AIF.
`If the AIF is lean, at step 64 a flag indicating a catalyst
`midbed over-temperature if A/F lean (EXT_FLG_LEAN)
`is set. If there is no midbed over-temperature (step 60), or if
`the NF is not lean (step 62), the ECU determines if there has
`been a torque reduction request at step 66. If there is no
`torque reduction request, the flag is cleared at step 68.
`With continuing reference to FIG. 3a, at step 70 the ECU
`checks the state of the EXT_FLG, a flag the state of which
`indicates rich NP and a catalyst exhaust midbed over-
`temperature flag. A state of ‘1’ indicates a rich AIF and
`catalyst midbed temperature under A/F control. If an over-
`temperature condition exists (EXT_FLGz l), at step 72 the
`ECU determines whether the A/F ratio is at the rich limit,
`such as by comparing the value of DES_LAMBSE to
`LAM_EXT_MIN,
`the variable representing the lowest
`LAMBSE the open-loop A/F controller will utilize to control
`catalyst temperatures. If DES_LAMBSE is at the rich limit,
`then the catalyst midbed temperature is presumed to be at or
`over the control limit. If either of the conditions tested at
`steps 70 and 72 fail, control flow proceeds to step 74, at
`which the state of the EXT_FLG_LEAN flag is checked. A
`
`90f12
`
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`
`9 of 12
`
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`
`

`

`5
`
`5,479,898
`
`6
`spkNRM=miu(SPK_BASE,SPK_BDL,SPK,_LOW_LOAD)
`
`(3)
`
`state of ‘1’ indicates a catalyst midbed over-temperature
`with a lean A/F.
`
`If control flow reaches step 76, there is an over-tempera-
`ture condition which precludes the use of spark retard for
`achieving the desired reduction in engine torque. Accord-
`ingly, at step 76 spark retard is disallowed, and fuel is cut
`from the fuel injectors. More particularly, at least one fuel
`injector per bank is turned off for cooling in the event a
`catalyst over-temperature condition exists. If there is no
`over-temperature condition, at step 78 the minimum torque
`ratio (TR_SPK_LVL) attainable by spark retard only is
`assigned utilizing a function which determines the maxi-
`mum amount of spark reduction (in terms of a torque ratio)
`that can be used before cylinder cutout and A/F scheduling
`are utilized. The maximum amount of spark reduction is
`preferably determined based on the source of the torque
`reduction request (TQ_SOURCE).
`Referring now to FIG. 4,
`there is shown a graphical
`illustration of the relationship between TR_SPK_LVL and
`TQ_SOURCE, wherein a TQSOURCE of 0: no torque
`reduction
`request;
`TQ_SOURCE
`of
`1:
`'ITL;
`TQ_SOURCE of 2: TCTL; TQ_SOURCE of 3: VSL;
`TQ_SOURCE of 4: ESL, TQ_SOURCE of 5: TITL; and
`TQ_ SOURCE of 6: TOTL. For example, a TR_SPK“
`LVL of 0.9 corresponds to 10% reduction by spark retard.
`Also at step 78, the number of cylinders eligible to be fueled
`is determined, since there is no over-temperature condition.
`Referring now to FIG. 3b, at step 80 the ECU determines
`a ratio of desired indicated torque over current indicated
`torque. The indicated torque is based on the desired net
`torque (TQ_MAX_ALLOW) and losses:
`
`(1)
`
`TQ_MAX_ALLOW + TQ_LOSS
`TQ_MBT
`tr_des =
`This ratio (tr_des) is then preferably utilized to determine
`the appropriate control action at step 82, wherein trwdes is
`compared to TR_SPK_LVL.
`If tr_des is
`less
`than
`TR_SPK_LVL, then the reduction to the desired net torque
`cannot be achieved by spark retard alone and the state of a
`flag (INJ_FLG) is modified accordingly at step 84. If tr_des
`exceeds TR_SPK_LVL, a torque ratio hysteresis is utilized
`at step 86. The value of the hysteresis adder, which is
`preferably added to TR_SPK_LVL prior to the comparison
`with tr_des, is set such that once engine cylinders are
`defueled, they remain defueled until a sizable increase in
`torque, such as 6% of a cylinder’s torque output (for a V8),
`is detected. At step 88, the INJ_FLG is cleared.
`With continuing reference to FIG. 3b, at step 90 the ECU
`checks the state of the INJ_FLG. If spark retard alone is
`sufiicient to achieve the desired torque, control flow pro-
`ceeds to step 92, wherein 'all cylinders are fueled and the
`ECU determines the torque reduction as a ratio to be
`performed by spark retard as follows:
`
`SPK_TQ_RATIO=tr__des/1NJ_TR/FUNC623(DESJAMBSEIZ)
`
`wherein FUNC623(DES_LAMBSE) represents an engine
`torque multiplier as a function of A/F ratio. More particu—
`larly, FUNC623, shown graphically in FIG. 5, relates the
`effect of AIF on indicated torque. For purposes of step 92,
`NF is input to the function, which outputs a torque ratio
`(indicated torque over indicated torque at 14.6). As shown,
`FUNC623 is generally bell-shaped, the lean side of which
`can be inverted to obtain FUNC632, shown in FIG. 6.
`As shown in FIG. 3b, if more than spark retard is needed,
`at step 94 the normal spark advance (spkNRM) is determined
`as follows:
`
`10
`
`15
`
`20
`
`25
`
`30
`
`35
`
`4o
`
`45
`
`50
`
`55
`
`60
`
`65
`
`wherein SPKwBASE represents the desired spark advance
`for optimal emissions and driveability, SPK_BDL repre-
`sents borderline detonation spark limit, and SPK_LOW_
`LOAD represents the idle emissions spark ceiling. At step
`96, SPKNRM is utilized to determine the torque ratio that
`would exist at the normal spark if no torque control actions
`were required:
`
`tr_exst=FUNC766(SPK_MBT—spkNRM)
`
`(4)
`
`wherein SPK_MBT is the spark advance required to
`achieve maximum brake torque. FUNC766, which is shown
`graphically in FIG. 7, is a function which relates a spark that
`is offset, or retarded, from the value required for maximum
`brake torque and a torque ratio.
`As shown in FIG. 7, the input, shown along the horizontal
`axis, is the amount the spark is retarded from MBT spark,
`measured in degrees (°). The output, shown along the
`vertical axis, is the ratio of delivered engine torque at a
`particular spark advance to the engine torque delivered when
`the engine is operating at MBT spark. In other words, when
`the engine is operating at MBT spark, the torque ratio is 1.0
`and when the operating point is retarded from MBT spark,
`the resulting torque ratio will be a dimensionless fractional
`value, such as 0.80 or 0.90.
`This function is described in greater detail in US. Pat. No.
`5,253,623, assigned to the assignee of the present invention,
`the specification of which is hereby incorporated by refer-
`ence in its entirety.
`'
`With continuing reference to FIG. 3b, at step 98 the ECU
`determines the minimum torque ratio required of injector
`cutout (trmin__tq). In detemiining that, the desired torque
`ratio is adjusted for any reductions already being executed
`by spark retard and for the minimum reduction expected to
`be performed by NP scheduling:
`
`tr_inj_tq=tr_des*NUMCYlJtr_exsth‘R_LAM_MIN
`
`(5)
`
`wherein TR_LAM_MIN represents the minimum torque
`reduction (in terms of a torque ratio) that would be realized
`due to A/F scheduling, and NUMCYL represents the number
`of engine cylinders. The result of this calculation is then
`rounded up to the nearest whole number.
`With reference to FIG. So, at step 100 the ECU determines
`the number of engine cylinders to be fueled (INJON) as
`follows:
`
`INJON=min(lNJON_MAX, tr_iuj_tq)
`
`(6)
`
`wherein INJON_MAX represents the maximum number of
`fuel injectors to be energized. Thus, at least INJON_MAX
`injectors are on for catalyst protection (6.g. controlling
`catalyst temperatures). At step 102, the ECU determines the
`torque ratio (INJyTR) that could be achieved solely by
`defueling engine cylinders:
`
`INJ_TR =
`
`INJON
`NUMCYL
`
`(7)
`
`Thereafter, at step 104 of FIG. 3c, the ECU determines the
`torque reduction as a ratio to be performed by lean A/F
`scheduling (TR_AF), adjusting for the number of cylinders
`' already defueled:
`
`TR_AF=tr_des/INJ_TRItr_exst
`
`(3)
`
`wherein tr_exst represents the torque available from the
`existing level of spark.
`
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`

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`With continuing reference to FIG. 3c, at step 106, the
`ECU converts the A/F torque ratio into a corresponding A/F
`ratio (LAM__TQ) to achieve it:
`
`LAM_TQ=FUNC632(TR__AF)
`
`(9)
`
`wherein FUNC632, which is shown graphically in FIG. 6, is
`a function which maps the relationship of a desired torque
`ratio (desired indicated torque to indicated torque at 14.6) to
`a lean A/F ratio. It is preferable to maintain an NE of at least
`1.1 during torque reductions, as an A/F of 1.0 or less may be
`too rich for catalyst temperature reasons. At step 108, this
`MP is clipped or limited to the limits of combustion stability
`as follows:
`
`10
`
`DES_LAMBSE=min(LAM_TQ,FNMAXLAM(N,LOAD))
`
`(10)
`
`15
`
`wherein FNMAXLAM (shown graphically in FIG. 8) is a
`function which relates A/F to engine load.
`At step 110 of FIG. 30, the ECU determines the torque
`reduction as a ratio to be performed by spark retard, adjust-
`ing for cylinders defueled and for A/F reductions already
`being performed:
`
`SPK_TQ_RATIO=tr_des/INJ_TRIFUNC623(DES_LAMBSE)1)
`
`It is understood, of course, that while the form of the
`invention herein shown and described constitutes the pre-
`ferred embodiment of the invention, it is not intended to
`illustrate all possible forms thereof. It will also be under-
`stood that the words used are words of description rather
`than limitation,'and that various changes may be made
`without departing from the spirit and scope of the invention
`as disclosed.
`What is claimed is:
`
`-
`
`1. An apparatus for controlling torque output of a spark
`ignition internal combustion engine having multiple cylin-
`ders, an air and fuel mixture flow control and fuel injectors
`for each of said cylinders, a fuel cut-out control for said
`injectors and a spark timing control, a microprocessor pro-
`grammed for establishing control signals to effect responses
`of said mixture control, said cut—out control and said spark
`timing control, said microprocessor having means for
`receiving operating condition sensor output
`information
`including mass air flow, engine speed, vehicle speed and
`throttle position, said microprocessor further having a con-
`trol unit and memory registers, said memory registers stor-
`ing control functions and being addressable by said control
`unit as said control unit operates on said sensor output
`information:
`
`20
`
`25
`
`30
`
`35
`
`40
`
`45
`
`wherein said microprocessor identifies a desired torque
`that is the lowest torque to which the engine torque is
`to be reduced;
`
`50
`
`wherein said microprocessor determines a first torque
`reduction to be achieved by defueling at least one of
`said engine cylinders;
`wherein said microprocessor further detemrines a second
`torquereduction to be achieved by lean air/fuel sched-
`uling, adjusted for the number of cylinders defueled;
`wherein said microprocessor further determines a third
`torque reduction to be achieved by spark timing retar-
`dation, adjusted for the number of cylinders defueled
`and for the lean air/fuel scheduling,
`and means for selectively implementing said first, second
`and third torque reductions so as to reduce the engine
`torque to said desired engine torque including means
`for selectively activating said controls for air and fuel
`mixture flow, said fuel cut-out and said spark timing in
`
`55
`
`60
`
`65
`
`accordance with the establishment of predetermined
`values for said control signals.
`2. The apparatus of claim 1 wherein the engine torque
`being produced is reduced to said desired engine torque
`solely by retarding the spark advance when the reduction
`can be achieved solely by spark retard.
`3. The apparatus of claim 2 wherein the vehicle includes
`a catalytic converter through which engine exhaust passes,
`the apparatus further comprising a catalytic converter tem—
`perature sensor,
`said microprocessor
`further
`including
`means for precluding the use of spark retard to achieve the
`reduced engine torque when a catalytic converter over-
`temperature condition exists.
`4. The apparatus of claim 2 wherein said microprocessor
`further includes means for determining whether the desired
`engine torque can be obtained solely by spark retard.
`5. The apparatus of claim 1 wherein the number of
`cylinders to be fueled is determined according to:
`
`1NJON= min (INJON_MAX, tr_inj_tq)
`
`wherein INJON_MAX represents the maximum number
`of fuel injectors to be energized and tr_inj_tq repre-
`sents the minimum torque ratio required of injector
`cutout.
`
`6. The apparatus of claim 1 wherein said first torque
`reduction is determined according to:
`
`INJON
`[NJ—TR : NUMCYL
`
`wherein NUMCYL represents the number of cylinders in
`the engine.
`7. The apparatus of claim 1 wherein said second torque
`reduction is determined according to:
`
`TR_AF= tr_des/INJ_TR/t1'__exst
`
`and wherein tr_des represents a ratio of desired indicated
`torque over current indicated torque, INJ_TR repre-
`sents a torque ratio that could be achieved solely by
`defueling engine cylinders, add tr_exst represents the
`torque available from the existing level of spark.
`8. The apparatus of claim 7 wherein said microprocessor
`further comprises means for converting TR_AF into a
`corresponding air/fuel ratio utilizing a function which relates
`torque ratios to air/fuel ratios.
`9. The apparatus of claim 8 wherein said microprocessor
`further comprises means for limiting the corresponding
`air/fuel ratio to the limits of combustion stability utilizing a '
`function which relates air/fuel to engine load.
`10. The apparatus of claim 1 wherein said third torque
`reduction is determined according to:
`
`SPK~TQ_RATIO= tr_des/INJ_TR/FUNC623 (DES_LAMBSE)
`
`wherein FUNC623 (DES_LAMBSE) is a function which
`relates the effect of A/F on indicated torque.
`11. A powertrain control for a wheeled vehicle having
`traction wheels, a spark ignition, internal combustion engine
`having multiple cylinders, and a transmission drivably con-
`necting said engine to said traction wheels, an apparatus for
`controlling torque output of said engine, said engine cylin-
`ders having an air and fuel mixture flow control and fuel
`injectors for each of said cylinders, a fuel cut-out control for
`said injectors and a spark timing control, a microprocessor
`means programmed for establishing control signals to effect
`
`11 of12
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`

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`a response of said mixture flow, said cut—out and said spark
`timing, said microprocessor having means for receiving
`operating condition sensor information including mass air
`flow, engine speed, vehicle speed and throttle position, a
`control unit and memory registers, said memory registers
`storing control functions and being addressable by said
`control unit as said control unit operates on said sensor
`output information:
`wherein said microprocessor identifies a desired torque to
`which the engine torque is to be reduced;
`wherein said microprocessor determines a first torque
`reduction to be achieved by defueling at least one of the
`engine cylinders;
`wherein said microprocessor further determines a second
`torque reduction to be achieved by lean air/fuel sched—
`uling, adjusted for the number of cylinders defueled;
`wherein s