# Patent

## Title
Method and control architecture for selection of optimal engine input torque for a powertrain system

## Abstract

A method and article of manufacture are provided for operating an internal combustion engine adapted to transmit torque to a hybrid transmission. The method comprises determining engine input torque transmittable to the hybrid transmission for each of a plurality of engine states. Costs are determined for operating the engine and hybrid transmission in the engine states to substantially meet an operator torque request. A preferred engine state is selected based upon the determined costs. The engine is controlled based upon the preferred engine state to substantially meet an operator torque request.

## Background
TECHNICAL FIELD
This invention pertains generally to control systems for powertrain control systems employing electro-mechanical transmissions.
BACKGROUND OF THE INVENTION
The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
Powertrain architectures comprise torque-generative devices, including internal combustion engines and electric machines, which transmit torque through a transmission device to a vehicle driveline. One such transmission includes a two-mode, compound-split, electro-mechanical transmission which utilizes an input member for receiving motive torque from a prime mover power source, typically an internal combustion engine, and an output member for delivering motive torque from the transmission to the vehicle driveline. Electrical machines, operatively connected to an electrical energy storage device, comprise motor/generators operable to generate motive torque for input to the transmission, independently of torque input from the internal combustion engine. The electrical machines are further operable to transform vehicle kinetic energy, transmitted through the vehicle driveline, to electrical energy potential that is storable in the electrical energy storage device. A control system monitors various inputs from the vehicle and the operator and provides operational control of the powertrain system, including controlling transmission gear shifting, controlling the torque-generative devices, and regulating the electrical power interchange between the electrical energy storage device and the electrical machines.
The exemplary electro-mechanical transmissions are selectively operative in fixed gear modes and continuously variable modes through actuation of the torque-transfer clutches, typically employing a hydraulic circuit to effect clutch actuation. A fixed gear mode occurs when rotational speed of the transmission output member is a fixed ratio of rotational speed of the input member from the engine, typically due to actuation of one or more torque-transfer clutches. A continuously variable mode occurs when rotational speed of the transmission output member is variable based upon operating speeds of one or more electrical machines. The electrical machines can be connected to the output shaft via actuation of a clutch, or by direct connection. Clutch actuation and deactivation is typically effected through a hydraulic circuit.
Engineers implementing powertrain systems having electro-mechanical transmissions are tasked with implementing control schemes to monitor system states and control operation of various systems and actuators to effectively control powertrain operation. Such a system is described hereinafter.
SUMMARY OF THE INVENTION
In accordance with an embodiment of the invention, there is a method for operating an internal combustion engine adapted to transmit torque to a hybrid transmission. The method comprises determining engine input torque transmittable to the hybrid transmission for each of a plurality of engine states. Costs are determined for operating the engine and hybrid transmission in the engine states to substantially meet an operator torque request. A preferred engine state is selected based upon the determined costs. The engine is controlled based upon the preferred engine state to substantially meet an operator torque request.
An aspect of the invention comprises the method intended for execution in a control system for a hybrid powertrain system including the internal combustion engine and an electro-mechanical transmission. The control system preferably comprises a distributed control module architecture comprising a plurality of signally connected control modules including a hybrid control module, an engine control module, a transmission control module, and, a power inverter control module. The transmission is selectively operative in a plurality of fixed gear modes and continuously variable modes through selective actuation of a plurality of torque-transfer clutches.
These and other aspects of the invention will become apparent to those skilled in the art upon reading and understanding the following detailed description of the embodiments.



BRIEF DESCRIPTION OF THE DRAWINGS
The invention may take physical form in certain parts and arrangement of parts, an embodiment of which is described in detail and illustrated in the accompanying drawings which form a part hereof, and wherein:
FIG. 1 is a schematic diagram of an exemplary powertrain, in accordance with the present invention;
FIG. 2 is a schematic diagram of an exemplary architecture for a control system and powertrain, in accordance with the present invention; and,
FIGS. 3-7 are algorithmic flow diagrams, in accordance with the present invention.



DETAILED DESCRIPTION OF AN EMBODIMENT OF THE INVENTION
Referring now to the drawings, wherein the showings are for the purpose of illustrating the invention only and not for the purpose of limiting the same, a tactical control scheme for operating an internal combustion engine adapted to transmit torque to a hybrid transmission system is now described. The tactical control scheme, depicted with reference to FIGS. 3-7 is preferably executed as one or more algorithms in an electronic control module.
The method comprises determining engine input torque transmittable to the hybrid transmission for each of a plurality of engine states, and determining preferred costs for the engine states. A preferred engine state and associated engine torque are selected, based upon the costs for the engine states. The engine operation is controlled based upon the preferred engine state which is effective to substantially meet an operator torque request.
The method includes monitoring an output of the hybrid transmission, typically rotational speed of an output shaft NO. Tactical control 130 is executed to determine the input torque commanded (or desired) from the internal combustion engine and a desired engine state. Key inputs to tactical control preferably comprise: the transmission output speed, NO, engine input speed, NI, current engine state and allowability of various engine states, the operator torque request, TO—REQ, and the current actual operating range state of the transmission. Exemplary current engine states comprise normal engine operation (‘ALL_CYL’), engine operation with deactivated cylinders (‘DEACT’), engine fuel-cutoff (‘FCO’), and engine fuel-cutoff with cylinder deactivation (‘FCO_DEACT’). The engine fuel-cutoff states are characterized by the engine rotatably operatively connected to the transmission. Engine state allowability is an indication that the engine operation can be effectively transitioned to one or more of the engine states without undue operator discomfort or disruption, and is typically based upon engine operating conditions. Specifically the engine state allowability preferably indicates allowability of each of the cylinder deactivation and the engine fuel-cutoff states. Controlling the input torque from the internal combustion engine comprises controlling operation of the engine to a preferred speed/load operating point to achieve the engine input torque, in one of the engine states, preferably without violating other operating conditions and requirements, including those related to driveability, fuel economy, and emissions. This is discussed in detail hereinafter.
Referring now to FIGS. 1 and 2, an exemplary hybrid powertrain system is depicted, comprising an engine 14, transmission 10, control system, and driveline 90 which has been constructed in accordance with an embodiment of the present invention. The tactical control scheme depicted in FIGS. 3-7 is executed to control operation of the exemplary hybrid powertrain system depicted with reference to FIGS. 1 and 2. Mechanical aspects of the exemplary transmission 10 are disclosed in detail in commonly assigned U.S. Pat. No. 6,953,409, entitled “Two-Mode, Compound-Split, Hybrid Electro-Mechanical Transmission having Four Fixed Ratios”, which is incorporated herein by reference. The exemplary two-mode, compound-split, electro-mechanical hybrid transmission embodying the concepts of the present invention is depicted in FIG. 1. The transmission 10 includes an input shaft 12 having an input speed, NI that is preferably driven by the internal combustion engine 14, and an output shaft 64 having an output rotational speed, NO. The engine 14 has a crankshaft having characteristic speed NE which is operatively connected to the transmission input shaft 12. When a torque converter clutch device (not shown) operatively connects the engine and transmission, the engine speed NE and output torque TE can differ from transmission input speed NI and engine input torque TI.
The transmission 10 utilizes three planetary-gear sets 24, 26 and 28, and four torque-transmitting devices, i.e., clutches C1 70, C2 62, C3 73, and C4 75. An electro-hydraulic control circuit 42, preferably controlled by transmission control module (‘TCM’) 17, controls actuation and deactivation of the clutches. Clutches C2 and C4 preferably comprise hydraulically-actuated rotating friction clutches. Clutches C1 and C3 preferably comprise comprising hydraulically-actuated stationary devices grounded to the transmission case 68.
There is first electrical machine comprising a motor/generator 56, referred to as MG-A, and a second electrical machine comprising a motor/generator 72, referred to as MG-B operatively connected to the transmission via the planetary gears. Transmission output shaft 64 is operably connected to a vehicle driveline 90 to provide motive output torque, TO to vehicle wheels. Each clutch is preferably hydraulically actuated, receiving pressurized hydraulic fluid from a pump, described below, via an electro-hydraulic control circuit 42.
The transmission 10 receives input torque from the torque-generative devices, including the engine 14 and the MG-A 56 and MG-B 72, and referred to as ‘TI’, ‘TA’, and ‘TB’ respectively, as a result of energy conversion from fuel or electrical potential stored in an electrical energy storage device (ESD) 74. The ESD 74 is high voltage DC-coupled to transmission power inverter module (‘TPIM’) 19 via DC transfer conductors 27. The TPIM 19 is an element of the control system described hereinafter with regard to FIG. 2. The TPIM 19 transmits electrical energy to and from MG-A 56 by transfer conductors 29, and the TPIM 19 similarly transmits electrical energy to and from MG-B 72 by transfer conductors 31. Electrical current is transmitted to and from the ESD 74 in accordance with whether the ESD 74 is being charged or discharged. TPIM 19 includes the pair of power inverters and respective motor control modules configured to receive motor control commands and control inverter states therefrom for providing motor drive or regeneration functionality. Preferably, MG-A 56 and MG-B 72 are three-phase AC machines each having a rotor operable to rotate within a stator that is mounted on a case of the transmission. The inverters comprise known complementary three-phase power electronics devices.
Referring now to FIG. 2, a schematic block diagram of the control system, comprising a distributed control module architecture, is shown. The elements described hereinafter comprise a subset of an overall vehicle control architecture, and are operable to provide coordinated system control of the powertrain system described herein. The control system is operable to synthesize pertinent information and inputs, and execute algorithms to control various actuators to achieve control targets, including such parameters as fuel economy, emissions, performance, driveability, and protection of hardware, including batteries of ESD 74 and MG-A and MG-B 56, 72. The distributed control module architecture includes engine control module (‘ECM’) 23, transmission control module (‘TCM’) 17, battery pack control module (‘BPCM’) 21, and TPIM 19. A hybrid control module (‘HCP’) 5 provides overarching control and coordination of the aforementioned control modules. There is a User Interface (‘UI’) 13 operably connected to a plurality of devices through which a vehicle operator typically controls or directs operation of the powertrain including the transmission 10 through a request for a torque output. Exemplary vehicle operator inputs to the UI 13 include an accelerator pedal, a brake pedal, transmission gear selector, and, vehicle speed cruise control. Each of the aforementioned control modules communicates with other control modules, sensors, and actuators via a local area network (‘LAN’) bus 6. The LAN bus 6 allows for structured communication of control parameters and commands between the various control modules. The specific communication protocol utilized is application-specific. The LAN bus and appropriate protocols provide for robust messaging and multi-control module interfacing between the aforementioned control modules, and other control modules providing functionality such as antilock brakes, traction control, and vehicle stability.
The HCP 5 provides overarching control of the hybrid powertrain system, serving to coordinate operation of the ECM 23, TCM 17, TPIM 19, and BPCM 21. Based upon various input signals from the UT 13 and the powertrain, including the battery pack, the HCP 5 generates various commands, including: an operator torque request (‘TO—REQ’) output to driveline 90, the engine input torque TI originating from the engine, clutch torque, (‘TCL—N’) for the N various torque-transfer clutches C1, C2, C3, C4 of the transmission 10; and motor torques TA and TB for MG-A and MG-B. The TCM 17 is operatively connected to the electro-hydraulic control circuit 42, including monitoring various pressure sensing devices (not shown) and generating and executing control signals for various solenoids to control pressure switches and control valves contained therein.
The ECM 23 is operably connected to the engine 14, and functions to acquire data from a variety of sensors and control a variety of actuators, respectively, of the engine 14 over a plurality of discrete lines collectively shown as aggregate line 35. The ECM 23 receives the engine input torque command from the HCP 5, and generates a desired axle torque, and an indication of actual engine input torque, TI, to the transmission, which is communicated to the HCP 5. For simplicity, ECM 23 is shown generally having bi-directional interface with engine 14 via aggregate line 35. Various other parameters that may be sensed by ECM 23 include engine coolant temperature, engine input speed, NE, to shaft 12 which translate to transmission input speed, NI, manifold pressure, ambient air temperature, and ambient pressure. Various actuators that may be controlled by the ECM 23 include fuel injectors, ignition modules, and throttle control modules.
The TCM 17 is operably connected to the transmission 10 and functions to acquire data from a variety of sensors and provide command signals to the transmission. Inputs from the TCM 17 to the HCP 5 include estimated clutch torques (TCL—EST—N) for each of the N clutches, i.e., C1, C2, C3, and C4, and rotational speed, NO, of the output shaft 64. Other actuators and sensors may be used to provide additional information from the TCM to the HCP for control purposes. The TCM 17 monitors inputs from pressure switches and selectively actuates pressure control solenoids and shift solenoids to actuate various clutches to achieve various transmission operating modes, as described hereinbelow.
The BPCM 21 is signally connected one or more sensors operable to monitor electrical current or voltage parameters of the ESD 74 to provide information about the state of the batteries to the HCP 5. Such information includes battery state-of-charge, battery voltage and available battery power, referred to as a range PBAT—MIN to PBAT—MAX.
Each of the aforementioned control modules is preferably a general-purpose digital computer generally comprising a microprocessor or central processing unit, storage mediums comprising read only memory (ROM), random access memory (RAM), electrically programmable read only memory (EPROM), high speed clock, analog to digital (A/D) and digital to analog (D/A) circuitry, and input/output circuitry and devices (I/O) and appropriate signal conditioning and buffer circuitry. Each control module has a set of control algorithms, comprising resident program instructions and calibrations stored in ROM and executed to provide the respective functions of each computer. Information transfer between the various computers is preferably accomplished using the aforementioned LAN 6.
Algorithms for control and state estimation in each of the control modules are typically executed during preset loop cycles such that each algorithm is executed at least once each loop cycle. Algorithms stored in the non-volatile memory devices are executed by one of the central processing units and are operable to monitor inputs from the sensing devices and execute control and diagnostic routines to control operation of the respective device, using preset calibrations. Loop cycles are typically executed at regular intervals, for example each 3.125, 6.25, 12.5, 25 and 100 milliseconds during ongoing engine and vehicle operation. Alternatively, algorithms may be executed in response to occurrence of an event.
The exemplary two-mode, compound-split, electro-mechanical transmission operates in one of several operating range states comprising fixed gear operation and continuously variable operation, described with reference to FIG. 1, and Table 1, below.










TABLE 1






Transmission Operating





Range State (‘Op_range’)
Actuated Clutches



















Mode I - Engine Off (M1_Eng_Off)
C1 70




Mode I - Engine On (M1_Eng_On)
C1 70




Fixed Ratio 1 (GR1)
C1 70
C4 75



Fixed Ratio 2 (GR2)
C1 70
C2 62



Mode II - Engine Off
C2 62




(M2_Eng_Off)





Mode II - Engine On (M2_Eng_On)
C2 62




Fixed Ratio 3 (GR3)
C2 62
C4 75



Fixed Ratio 4 (GR4)
C2 62
C3 73









The various transmission operating range states described in the table indicate which of the specific clutches C1, C2, C3, and C4 are engaged or actuated for each of the operating range states. A first mode, i.e., Mode I, is selected when clutch C1 70 is actuated in order to “ground” the outer gear member of the third planetary gear set 28. The engine 14 can be either on or off. A second mode, i.e., Mode II, is selected when clutch C1 70 is released and clutch C2 62 is simultaneously actuated to connect the shaft 60 to the carrier of the third planetary gear set 28. Again, the engine 14 can be either on or off. For purposes of this description, Engine Off is defined by engine input speed, NE, being equal to zero revolutions per minute (RPM), i.e., the engine crankshaft is not rotating, typically as a result of the engine being decoupled from the transmission. Other factors outside the scope of the invention affect when the electrical machines 56, 72 operate as motors and generators, and are not discussed herein.
The first and second modes of operation refer to circumstances in which the transmission functions are controlled by one clutch, i.e., either clutch C1 62 or C2 70, and by the controlled speed and torque of the electrical machines 56 and 72, which can be referred to as a continuously variable transmission mode. Certain ranges of operation are described below in which fixed gear ratios are achieved by applying an additional clutch. This additional clutch may be clutch C3 73 or C4 75, as shown in the table, above. When the additional clutch is applied, fixed ratio operation of input-to-output speed of the transmission, i.e., NI/NO, is achieved. The rotations of machines MG-A and MG-B 56, 72 are dependent on internal rotation of the mechanism as defined by the clutching and proportional to the input speed measured at shaft 12.
In response to an operator's action, as captured by the UI 13, the supervisory HCP control module 5 and one or more of the other control modules determine the operator torque request TO—REQ, to be executed at shaft 64. Final vehicle acceleration is affected by other factors, including, e.g., road load, road grade, and vehicle mass. The operating mode is determined for the exemplary transmission based upon a variety of operating characteristics of the powertrain. This includes an operator demand for torque, typically communicated through inputs to the UI 13 as previously described. Additionally, a demand for output torque is predicated on external conditions, including, e.g., road grade, road surface conditions, or wind load. The operating mode may be predicated on a powertrain torque demand caused by a control module command to operate of the electrical machines in an electrical energy generating mode or in a torque generating mode. The operating mode can be determined by an optimization algorithm or routine operable to determine optimum system efficiency based upon operator demand for power, battery state of charge, and energy efficiencies of the engine 14 and MG-A and MG-B 56, 72. The control system manages torque inputs from the engine 14 and MG-A and MG-B 56, 72 based upon an outcome of the executed optimization routine, and system optimization occurs to optimize system efficiencies to improve fuel economy and manage battery charging. Furthermore, operation can be determined based upon a fault in a component or system. The HCP 5 monitors the parametric states of the torque-generative devices, and determines the output of the transmission required to arrive at the desired torque output, as described hereinbelow. Under the direction of the HCP 5, the transmission 10 operates over a range of output speeds from slow to fast in order to meet the operator demand.
The exemplary engine 14 comprises a multi-cylinder internal combustion engine selectively operative in several states to transmit torque to the transmission via shaft 12, and can be either a spark-ignition or a compression-ignition engine. The exemplary engine states comprise normal engine operation (‘ALL_CYL’), engine operation with deactivated cylinders (‘DEACT’), engine fuel-cutoff (‘FCO’), and engine fuel-cutoff with cylinder deactivation (‘FCO_DEACT’). In normal engine operation, all the engine cylinders are fueled and fired. In the cylinder deactivation state, typically half of the cylinders, e.g., one bank of a V-configured engine, are deactivated. A bank of cylinders is typically deactivated by discontinuing fuel delivery thereto and selectively leaving open exhaust valves to reduce engine pumping losses. In the engine fuel-cutoff state, fuel delivery to all the cylinders is discontinued. In the engine fuel-cutoff state with cylinder deactivation state, fuel delivery to all the cylinders is discontinued and a bank of the cylinders is deactivated to reduce pumping losses.
Referring again to FIGS. 3-7, a more detailed description of controlling operation of the hybrid powertrain is described, with reference to the exemplary powertrain system described in FIGS. 1 and 2. Referring to FIG. 3, the method and system described herein comprise an aspect of powertrain control optimization, wherein torque outputs from MG-A and MG-B are determined based upon operator torque request TO—REQ, input speed NI, and output speed NO. Strategic control optimization includes strategic control 110, shift execution and control 120, motor torque determination 140, and tactical control 130. Output of tactical control 130 includes the commanded or requested engine input torque, TI—CMD, input to the ECM 23 and a desired engine state, Engine_StateDES. The ECM 23 determines and outputs a parametric value for engine input torque, TI, for input to the motor torque determination block (Block 140). Other aspects of the overall architecture for optimization and control of the exemplary powertrain are described in co-pending U.S. patent application Ser. No. 11/561,140, entitled CONTROL ARCHITECTURE FOR OPTIMIZATION AND CONTROL OF A HYBRID POWERTRAIN SYSTEM which is incorporated by reference, and need not be described herein.
Referring now to FIG. 4, the tactical control method includes monitoring output of the transmission, typically NO. Tactical control 130 is executed to determine the engine input torque commanded (or desired) from the internal combustion engine, TI—CMD, and the desired engine state, Engine_StateDES, preferably during every 25 ms loop cycle, each which are output to the ECM 23 for execution therein. Key inputs to tactical control 130 preferably comprise the transmission output speed, NO, the engine input speed, NI, current engine state (‘Engine_State’) and engine state allowability (‘Eng_State_Allow’) from the ECM 23, the operator torque request, TO—REQ, and the current actual operating range state (‘Op_Range’) of the transmission as determined previously in Block 120. The engine input torque desired or commanded from the internal combustion engine, TI—CMD is communicated to the ECM 23 for execution therein. The aforementioned inputs to the tactical control 130 are input to a tactical manager 220, which generates outputs to a tactical system constraint block 240 and to a tactical optimization block 260. Output of the tactical system constraints 240 is also input to the tactical optimization 260. The outputs of tactical optimization 260 are input to the engine state stabilization and arbitration 280, the output of which comprises the engine input torque command, TI—CMD, and the desired engine state, Engine_StateDES.
Referring now to FIG. 5, inputs to the tactical manager 220 comprise the raw operator inputs to UI 13, e.g., operator inputs to the accelerator pedal and brake pedal. Cost structure information is communicated, comprising costs associated with operating the engine under specific operating conditions, calculated as described hereinbelow. Raw tactical inputs to the tactical manager 220 comprise current actual parametric data for the transmission operating range state (“Op_range”), NI, NO, and the operator torque request TO—REQ, engine state allowability, and limitations on power output from the ESD 74, i.e., PBAT—MIN, PBAT—MAX Outputs of the tactical manager 220 include cost structure inputs to the tactical optimization block 260, and tactical inputs of the current actual parametric data for the operating range state (“Op_range”), NI, NO, and the operator torque request TO—REQ for input to both the system constraints block 240 and the tactical optimization block 260.
Referring now to FIGS. 6 and 7, the actual parametric data for Op_range, NI, NO, and TO—REQ and battery power constraints PBAT—MIN and PBAT—MAX are input to torque constraints (Block 230) to determine constraints on the output torque, TO, of the system. The torque constraint segment 230 determines maximum and minimum engine input torques for operating in each of the engine states based upon input. The engine input torques for the operating states are referred to as normal state (TI—MIN—ALL—CYL, TI—MAX—ALL—CYL); cylinder deactivation state (TI—MIN—DEACT, TI—MAX—DEACT); the engine fuel cut-off state (TI—FCO); and, engine fuel cut-off and cylinder deactivation state (TI—FCO—DEACT). This information is communicated to the tactical systems constraints 240, and to the tactical optimization 260. The tactical systems constraints 240 also receives the actual parametric data for Op_range, NI, NO, and TO—REQ and battery power constraints PBAT—MIN and PBAT—MAX as inputs. The tactical systems constraints (Block 240) use the inputs to determine maximum and minimum engine input torque values for each engine operating condition.
The various engine input torque parameters or ranges are output to tactical optimization 260, shown along lines 242, 244, 246, 248, along with the TO—REQ, and the cost structure inputs from block 220. In tactical optimization 260, optimum operating points and associated costs for operating the engine in each operating state are determined based upon the inputs, including normal operation (TI—MIN—ALL—CYL, TI—MAX—ALL—CYL); cylinder deactivation state (TI—MIN—DEACT, TI—MAX—DEACT). For the engine fuel cut-off state (TI—FCO) and the engine fuel cut-off-cylinder deactivation state (TI—FCO—DEACT), there is an evaluation of system operating costs based upon the engine input torque, typically from the ECM, operator torque request, and the cost structure inputs. Thus, input from 242 is input to normal engine state optimization block 262, input from 244 is input to deactivated cylinders engine state optimization block 264, input from 246 is input to engine fuel-cutoff evaluation block 266, and, input from 248 is input to engine fuel-cutoff and deactivation evaluation block 268.
An optimum operating point preferably comprises an operating point attainable within the range of torque values for each engine state which expends a minimum operating cost, determined in segment 260. The outputs of the optimization segment 260 are input to the engine state stabilization and arbitration segment 280. Is this segment, one of the engine states input from tactical optimization 260 is selected as a preferred engine state based upon the calculated costs and other factors related to engine, powertrain and vehicle durability and stability. In the engine stabilization and arbitration (Block 280), an operating state (Engine_StateDES) and an optimum operating point (TI—CMD) are determined, and subsequently executed during the forthcoming loop cycle. Typically the selected engine state is the minimum cost operating state.
The cost information preferably comprises operating costs which are generally determined based upon factors related to vehicle driveability, fuel economy, emissions, and battery life for the determined torque range. When costs are determined for the engine state as engine fuel-cutoff (FCO), there are no fuel costs. Furthermore, costs are assigned and associated with fuel and electrical power consumption associated with a specific operating point of the powertrain system for the vehicle. Lower operating costs are generally associated with lower fuel consumption at high conversion efficiencies, lower battery power usage, and lower emissions for an operating point, and take into account a current operating range state of the powertrain system. The optimum operating cost (PCOST) can be determined by calculating a total powertrain system loss, comprising an overall system power loss and a cost penalty, such as can be associated with controlling battery state of charge. The overall system power loss comprises a term based upon engine power loss driven by fuel economy and exhaust emissions, plus losses in the mechanical system (e.g., gears, pumps, belts, pulleys, valves, chains), losses in the electrical system (e.g., wire impedances and switching and solenoid losses), and heat losses. Other losses include electrical machine power losses and internal battery power losses. Other factors may also be considered, including factors related to battery life due to depth of discharge of the ESD 74, current ambient temperatures and their effect on state of charge of the battery. Operating costs are preferably developed relative to specific powertrain/vehicle applications during vehicle calibration pre-production. An exemplary method for determining engine power losses are described in commonly assigned U.S. Patent Application Publication Number 2005/0256633 A2, entitled COST STRUCTURE METHOD INCLUDING FUEL ECONOMY AND ENGINE EMISSION CONSIDERATIONS, the contents of which are incorporated herein by reference.
It is understood that modifications are allowable within the scope of the invention. The invention has been described with specific reference to the embodiments and modifications thereto. Further modifications and alterations may occur to others upon reading and understanding the specification. It is intended to include all such modifications and alterations insofar as they come within the scope of the invention.

## Claims

1. Method for operating an internal combustion engine adapted to transmit torque to a hybrid transmission, comprising:
determining an engine input torque range transmittable to the hybrid transmission for each respective engine state of a plurality of engine states;
determining costs for operating the engine and hybrid transmission in the determined engine input torque range for each respective engine state to substantially meet an operator torque request, the determined costs based on factors related to vehicle drivability, fuel economy, emissions and battery life;
selecting a preferred engine state and a preferred engine input torque based upon the determined costs; and,
controlling the engine based upon the preferred engine state and the preferred engine input torque to substantially meet an operator torque request.

2. The method of claim 1, wherein the engine states comprise a normal engine operating state, a cylinder deactivation state, an engine fuel-cutoff state, and, an engine fuel-cutoff state with cylinder deactivation.

3. The method of claim 2, wherein determining costs comprises determining a minimum powertrain system operating cost and an associated engine input torque to substantially meet the operator torque request at the minimum powertrain system operating cost when the engine state comprises one of the normal engine state and the cylinder deactivation state.

4. The method of claim 3, wherein determining costs comprises evaluating operation of the powertrain system to determine an operating cost to substantially meet the operator torque request when the engine state comprises one of the engine fuel cut-off state and the engine fuel cut-off state with cylinder deactivation.

5. The method of claim 1, further comprising determining an engine input torque range transmittable to the hybrid transmission for each respective engine state of the plurality of engine states based upon a current operating range of the hybrid transmission.

6. The method of claim 5, wherein the current operating range of the hybrid transmission comprises one of a plurality of fixed gear modes and two continuously variable modes.

7. The method of claim 1, further comprising controlling the engine to an allowable engine state.

8. The method of claim 1, wherein controlling the engine based upon the preferred engine state and the preferred engine input torque to substantially meet an operator torque request comprises controlling engine input torque to the hybrid transmission.

9. The method of claim 8, further comprising controlling the engine input torque and a desired engine state.

10. The method of claim 1, wherein the engine input torque range transmittable to the hybrid transmission for each respective engine state of the plurality of engine states is determinable based upon the operator torque request, engine operating conditions, and engine operating constraints.

11. Method for operating a powertrain comprising an internal combustion engine and first and second electrical machines and an electro-mechanical transmission selectively operative to transmit torque therebetween and to transmit torque to a driveline, the method comprising:
determining allowable engine states and an operator torque request;
determining an engine input torque range transmittable to the hybrid powertrain system at each respective allowable engine state;
determining powertrain system costs for operating the engine and hybrid transmission in the engine input torque range for each respective allowable engine state to substantially meet the operator torque request, the determined powertrain system costs based on factors related to vehicle drivability, fuel economy, emissions and battery life;
selecting a preferred engine state and a preferred engine input torque based upon the determined powertrain system costs for the allowable engine states; and,
controlling the engine based upon the preferred engine state and a preferred engine input torque to substantially meet the operator torque request.

12. The method of claim 11, further comprising commanding operation of the engine to the preferred engine state.

13. The method of claim 11, wherein the engine input torque range for each respective engine state is determined based upon an engine input speed to the transmission, a transmission output speed, a current operating range state of the transmission, the operator torque request, and available power from an electrical storage device operatively connected to the first and second electrical machines.