Method for operating a powertrain system to transition between engine states

A powertrain system includes a multi-cylinder engine coupled to a hybrid transmission. The engine is selectively operative in one of a plurality of main engine states to transfer engine torque to the hybrid transmission. A method for operating a powertrain system includes monitoring an operator torque request, determining a preferred main engine state and a preferred engine torque associated with the preferred engine state, determining an engine state transition path from a present main engine state to the preferred main engine state including an engine transition state, and executing the engine state transition path between the present main engine state and the preferred main engine state and adjusting engine torque to the preferred engine torque.

TECHNICAL FIELD

This disclosure pertains to control systems for hybrid powertrain systems.

BACKGROUND

Known hybrid powertrain architectures can include multiple torque-generative devices, including internal combustion engines and non-combustion torque machines, e.g., electric machines, which transmit torque through a transmission device to an output member. One exemplary hybrid powertrain includes a two-mode, compound-split, electro-mechanical transmission which utilizes an input member for receiving tractive torque from a prime mover power source, preferably an internal combustion engine, and an output member. The output member can be operatively connected to a driveline for a motor vehicle for transmitting tractive torque thereto. Machines, operative as motors or generators, can generate torque inputs to the transmission independently of a torque input from the internal combustion engine. The Machines may transform vehicle kinetic energy transmitted through the vehicle driveline to energy that is storable in an energy storage device. A control system monitors various inputs from the vehicle and the operator and provides operational control of the hybrid powertrain, including controlling transmission operating range state and gear shifting, controlling the torque-generative devices, and regulating the power interchange among the energy storage device and the machines to manage outputs of the transmission, including torque and rotational speed.

SUMMARY

A powertrain system includes a multi-cylinder engine coupled to a hybrid transmission. The engine is selectively operative in one of a plurality of main engine states to transfer engine torque to the hybrid transmission. A method for operating a powertrain system includes monitoring an operator torque request, determining a preferred main engine state and a preferred engine torque associated with the preferred engine state, determining an engine state transition path from a present main engine state to the preferred main engine state including an engine transition state, and executing the engine state transition path between the present main engine state and the preferred main engine state and adjusting engine torque to the preferred engine torque.

DETAILED DESCRIPTION

Referring now to the drawings, wherein the showings are for the purpose of illustrating certain exemplary embodiments only and not for the purpose of limiting the same,FIGS. 1 and 2depict an exemplary hybrid powertrain. The exemplary hybrid powertrain in accordance with the present disclosure is depicted inFIG. 1, comprising a two-mode, compound-split, electro-mechanical hybrid transmission10operatively connected to an engine14and first and second electric machines (‘MG-A’)56and (‘MG-B’)72. The engine14and first and second electric machines56and72each generate power which can be transferred to the transmission10. The power generated by the engine14and the first and second electric machines56and72and transferred to the transmission10is described in terms of input and motor torques, referred to herein as TI, TA, and TBrespectively, and speed, referred to herein as NI, NA, and NB, respectively.

The exemplary engine14comprises a multi-cylinder internal combustion engine selectively operative in several states to transfer torque to the transmission10via an input shaft12, and can be either a spark-ignition or a compression-ignition engine. The engine14includes a crankshaft (not shown) operatively coupled to the input shaft12of the transmission10. A rotational speed sensor11monitors rotational speed of the input shaft12. Power output from the engine14, comprising rotational speed and engine torque, can differ from the input speed NIand the input torque TIto the transmission10due to placement of torque-consuming components on the input shaft12between the engine14and the transmission10, e.g., a hydraulic pump (not shown) and/or a torque management device (not shown).

The exemplary transmission10comprises three planetary-gear sets24,26and28, and four selectively engageable torque-transferring devices, i.e., clutches C170, C262, C373, and C475. As used herein, clutches refer to any type of friction torque transfer device including single or compound plate clutches or packs, band clutches, and brakes, for example. A hydraulic control circuit42, preferably controlled by a transmission control module (hereafter ‘TCM’)17, is operative to control clutch states. Clutches C262and C475preferably comprise hydraulically-applied rotating friction clutches. Clutches C170and C373preferably comprise hydraulically-controlled stationary devices that can be selectively grounded to a transmission case68. Each of the clutches C170, C262, C373, and C475is preferably hydraulically applied, selectively receiving pressurized hydraulic fluid via the hydraulic control circuit42.

The first and second electric machines56and72preferably comprise three-phase AC machines, each including a stator (not shown) and a rotor (not shown), and respective resolvers80and82. The motor stator for each machine is grounded to an outer portion of the transmission case68, and includes a stator core with coiled electrical windings extending therefrom. The rotor for the first electric machine56is supported on a hub plate gear that is operatively attached to shaft60via the second planetary gear set26. The rotor for the second electric machine72is fixedly attached to a sleeve shaft hub66.

Each of the resolvers80and82preferably comprises a variable reluctance device including a resolver stator (not shown) and a resolver rotor (not shown). The resolvers80and82are appropriately positioned and assembled on respective ones of the first and second electric machines56and72. Stators of respective ones of the resolvers80and82are operatively connected to one of the stators for the first and second electric machines56and72. The resolver rotors are operatively connected to the rotor for the corresponding first and second electric machines56and72. Each of the resolvers80and82is signally and operatively connected to a transmission power inverter control module (hereafter ‘TPIM’)19, and each senses and monitors rotational position of the resolver rotor relative to the resolver stator, thus monitoring rotational position of respective ones of first and second electric machines56and72. Additionally, the signals output from the resolvers80and82are interpreted to provide the rotational speeds for first and second electric machines56and72, i.e., NAand NB, respectively.

The transmission10includes an output member64, e.g. a shaft, which is operably connected to a driveline90for a vehicle (not shown), to provide output power to the driveline90that is transferred to vehicle wheels93, one of which is shown inFIG. 1. The output power at the output member64is characterized in terms of an output rotational speed NOand an output torque TO. A transmission output speed sensor84monitors rotational speed and rotational direction of the output member64. Each of the vehicle wheels93is preferably equipped with a sensor94adapted to monitor wheel speed, the output of which is monitored by a control module of a distributed control module system described with respect toFIG. 2, to determine vehicle speed, and absolute and relative wheel speeds for braking control, traction control, and vehicle acceleration management.

The input torque from the engine14and the motor torques from the first and second electric machines56and72(TI, TA, and TBrespectively) are generated as a result of energy conversion from fuel or electrical potential stored in an electrical energy storage device (hereafter ‘ESD’)74. The ESD74is high voltage DC-coupled to the TPIM19via DC transfer conductors27. The transfer conductors27include a contactor switch38. When the contactor switch38is closed, under normal operation, electric current can flow between the ESD74and the TPIM19. When the contactor switch38is opened electric current flow between the ESD74and the TPIM19is interrupted. The TPIM19transmits electrical power to and from the first electric machine56by transfer conductors29, and the TPIM19similarly transmits electrical power to and from the second electric machine72by transfer conductors31to meet the torque commands for the first and second electric machines56and72in response to the motor torques TAand TB. Electrical current is transmitted to and from the ESD74in accordance with whether the ESD74is being charged or discharged.

The TPIM19includes the pair of power inverters (not shown) and respective motor control modules (not shown) configured to receive the torque commands and control inverter states therefrom for providing motor drive or regeneration functionality to meet the commanded motor torques TAand TB. The power inverters comprise known complementary three-phase power electronics devices, and each includes a plurality of insulated gate bipolar transistors (not shown) for converting DC power from the ESD74to AC power for powering respective ones of the first and second electric machines56and72, by switching at high frequencies. The insulated gate bipolar transistors form a switch mode power supply configured to receive control commands. There is typically one pair of insulated gate bipolar transistors for each phase of each of the three-phase electric machines. States of the insulated gate bipolar transistors are controlled to provide motor drive mechanical power generation or electric power regeneration functionality. The three-phase inverters receive or supply DC electric power via DC transfer conductors27and transform it to or from three-phase AC power, which is conducted to or from the first and second electric machines56and72for operation as motors or generators via transfer conductors29and31respectively.

FIG. 2is a schematic block diagram of the distributed control module system. The elements described hereinafter comprise a subset of an overall vehicle control architecture, and provide coordinated system control of the exemplary hybrid powertrain described inFIG. 1. The distributed control module system synthesizes pertinent information and inputs, and executes algorithms to control various actuators to meet control objectives, including objectives related to fuel economy, emissions, performance, drivability, and protection of hardware, including batteries of ESD74and the first and second electric machines56and72. The distributed control module system includes an engine control module (hereafter ‘ECM’)23, the TCM17, a battery pack control module (hereafter ‘BPCM’)21, and the TPIM19. A hybrid control module (hereafter ‘HCP’)5provides supervisory control and coordination of the ECM23, the TCM17, the BPCM21, and the TPIM19. A user interface (‘UI’)13is operatively connected to a plurality of devices through which a vehicle operator controls or directs operation of the electro-mechanical hybrid powertrain. The devices include an accelerator pedal113(‘AP’), an operator brake pedal112(‘BP’), a transmission gear selector114(‘PRNDL’), and a vehicle speed cruise control (not shown). The transmission gear selector114may have a discrete number of operator-selectable positions, including the rotational direction of the output member64to enable one of a forward and a reverse direction.

The aforementioned control modules communicate with other control modules, sensors, and actuators via a local area network (hereafter ‘LAN’) bus6. The LAN bus6allows for structured communication of states of operating parameters and actuator command signals between the various control modules. The specific communication protocol utilized is application-specific. The LAN bus6and appropriate protocols provide for robust messaging and multi-control module interfacing between the aforementioned control modules, and other control modules providing functionality including e.g., antilock braking, traction control, and vehicle stability. Multiple communications buses may be used to improve communications speed and provide some level of signal redundancy and integrity. Communication between individual control modules can also be effected using a direct link, e.g., a serial peripheral interface (‘SPI’) bus (not shown).

The HCP5provides supervisory control of the hybrid powertrain, serving to coordinate operation of the ECM23, TCM17, TPIM19, and BPCM21. Based upon various input signals from the user interface13and the hybrid powertrain, including the ESD74, the HCP5determines an operator torque request, an output torque command, an engine input torque command, clutch torque(s) for the applied torque-transfer clutches C170, C262, C373, C475of the transmission10, and the motor torques TAand TBfor the first and second electric machines56and72.

The ECM23is operatively connected to the engine14, and functions to acquire data from sensors and control actuators of the engine14over a plurality of discrete lines, shown for simplicity as an aggregate bi-directional interface cable35. The ECM23receives the engine input torque command from the HCP5. The ECM23determines the actual engine input torque, TI, provided to the transmission10at that point in time based upon monitored engine speed and load, which is communicated to the HCP5. The ECM23monitors input from the rotational speed sensor11to determine the engine input speed to the input shaft12, which translates to the transmission input speed, NI. The ECM23monitors inputs from sensors (not shown) to determine states of other engine operating parameters including, e.g., a manifold pressure, engine coolant temperature, ambient air temperature, and ambient pressure. The engine load can be determined, for example, from the manifold pressure, or alternatively, from monitoring operator input to the accelerator pedal113. The ECM23generates and communicates command signals to control engine actuators, including, e.g., fuel injectors, ignition modules, and throttle control modules, none of which are shown.

The TCM17is operatively connected to the transmission10and monitors inputs from sensors (not shown) to determine states of transmission operating parameters. The TCM17generates and communicates command signals to control the transmission10, including controlling the hydraulic control circuit42. Inputs from the TCM17to the HCP5include estimated clutch torques for each of the clutches, i.e., C170, C262, C373, and C475, and rotational output speed, NO, of the output member64. Other actuators and sensors may be used to provide additional information from the TCM17to the HCP5for control purposes. The TCM17monitors inputs from pressure switches (not shown) and selectively actuates pressure control solenoids (not shown) and shift solenoids (not shown) of the hydraulic control circuit42to selectively actuate the various clutches C170, C262, C373, and C475to achieve various transmission operating range states, as described hereinbelow.

The BPCM21is signally connected to sensors (not shown) to monitor the ESD74, including states of electrical current and voltage parameters, to provide information indicative of parametric states of the batteries of the ESD74to the HCP5. The parametric states of the batteries preferably include battery state-of-charge, battery voltage, battery temperature, and available battery power, referred to as a range PBAT—MINto PBAT—MAX.

A brake control module (hereafter ‘BrCM’)22is operatively connected to friction brakes (not shown) on each of the vehicle wheels93. The BrCM22monitors the operator input to the brake pedal112and generates control signals to control the friction brakes and sends a control signal to the HCP5to operate the first and second electric machines56and72based thereon.

Each of the control modules ECM23, TCM17, TPIM19, BPCM21, and BrCM22is preferably a general-purpose digital computer comprising a microprocessor or central processing unit, storage mediums comprising read only memory (‘ROM’), random access memory (‘RAM’), electrically programmable read only memory (‘EPROM’), a 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 of the control modules has a set of control algorithms, comprising resident program instructions and calibrations stored in one of the storage mediums and executed to provide the respective functions of each computer. Information transfer between the control modules is preferably accomplished using the LAN bus6and SPI buses. The control algorithms are 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 to monitor inputs from the sensing devices and execute control and diagnostic routines to control operation of the actuators, using preset calibrations. Loop cycles are executed at regular intervals, for example each 3.125, 6.25, 12.5, 25 and 100 milliseconds during ongoing operation of the hybrid powertrain. Alternatively, algorithms may be executed in response to the occurrence of an event.

The exemplary hybrid powertrain selectively operates in one of several states that can be described in terms of engine states comprising one of an engine-on state (‘ON’) and an engine-off state (‘OFF’), and transmission operating range states comprising a plurality of fixed gears and continuously variable operating modes, described with reference to Table 1, below.

Each of the transmission operating range states is described in the table and indicates which of the specific clutches C170, C262, C373, and C475are applied for each of the operating range states. A first continuously variable mode, i.e., EVT Mode1, or M1, is selected by applying clutch C170only in order to “ground” the outer gear member of the third planetary gear set28. The engine state can be one of ON (‘M1_Eng_On’) or OFF (‘M1_Eng_Off’). A second continuously variable mode, i.e., EVT Mode2, or M2, is selected by applying clutch C262only to connect the shaft60to the carrier of the third planetary gear set28. The engine state can be one of ON (‘M2_Eng_On’) or OFF (‘M2_Eng_Off’). For purposes of this description, when the engine state is OFF, the engine input speed is equal to zero revolutions per minute (‘RPM’), i.e., the engine crankshaft is not rotating. A fixed gear operation provides a fixed ratio operation of input-to-output speed of the transmission10, i.e., NI/NO. A first fixed gear operation (‘G1’) is selected by applying clutches C170and C475. A second fixed gear operation (‘G2’) is selected by applying clutches C170and C262. A third fixed gear operation (‘G3’) is selected by applying clutches C262and C475. A fourth fixed gear operation (‘G4’) is selected by applying clutches C262and C373. The fixed ratio operation of input-to-output speed increases with increased fixed gear operation due to decreased gear ratios in the planetary gears24,26, and28. The rotational speeds of the first and second electric machines56and72, NAand NBrespectively, are dependent on internal rotation of the mechanism as defined by the clutching and are proportional to the input speed measured at the input shaft12.

In response to operator input via the accelerator pedal113and brake pedal112as captured by the user interface13, the HCP5and one or more of the other control modules determine torque commands to control the torque generative devices comprising the engine14and the first and second electric machines56and72to meet the operator torque request at the output member64and transferred to the driveline90. Based upon input signals from the user interface13and the hybrid powertrain including the ESD74, the HCP5determines the operator torque request, a commanded output torque from the transmission10to the driveline90, an input torque from the engine14, clutch torques for the torque-transfer clutches C170, C262, C373, C475of the transmission10; and the motor torques for the first and second electric machines56and72, respectively, as is described hereinbelow.

Final vehicle acceleration can be affected by other factors including, e.g., road load, road grade, and vehicle mass. The engine state and the transmission operating range state are determined based upon a variety of operating characteristics of the hybrid powertrain. This includes the operator torque request communicated through the accelerator pedal113and brake pedal112to the user interface13as previously described. The transmission operating range state and the engine state may be predicated on a hybrid powertrain torque demand caused by a command to operate the first and second electric machines56and72in an electrical energy generating mode or in a torque generating mode. The transmission operating range state and the engine state can be determined by an optimization algorithm or routine which determines optimum system efficiency based upon operator demand for power, battery state of charge, and energy efficiencies of the engine14and the first and second electric machines56and72. The control system manages torque inputs from the engine14and the first and second electric machines56and72based upon an outcome of the executed optimization routine, and system efficiencies are optimized thereby, to manage fuel economy and battery charging. Furthermore, operation can be determined based upon a fault in a component or system. The HCP5monitors the torque-generative devices, and determines the power output from the transmission10at output member64that is required to meet the operator torque request while meeting other powertrain operating demands, e.g., charging the ESD74. As should be apparent from the description above, the ESD74and the first and second electric machines56and72are electrically-operatively coupled for power flow therebetween. Furthermore, the engine14, the first and second electric machines56and72, and the electro-mechanical transmission10are mechanically-operatively coupled to transfer power therebetween to generate a power flow to the output member64.

FIG. 3shows a control system architecture for controlling and managing signal flow in a hybrid powertrain system having multiple torque generative devices, described hereinbelow with reference to the hybrid powertrain system ofFIGS. 1 and 2, and residing in the aforementioned control modules in the form of executable algorithms and calibrations. The control system architecture is applicable to alternative hybrid powertrain systems having multiple torque generative devices, including, e.g., a hybrid powertrain system having an engine and a single electric machine, a hybrid powertrain system having an engine and multiple electric machines. Alternatively, the hybrid powertrain system can utilize non-electric torque-generative machines and energy storage systems, e.g., hydraulic-mechanical hybrid transmissions (not shown).

The control system architecture shows signal flow of a plurality of inputs to a strategic optimization control scheme (‘Strategic Control’)310, which determines a preferred input speed (‘Ni_Des’) and a preferred operating range state (‘Hybrid Range State Des’) based upon the output speed and the operator torque request, and optimized based upon other operating parameters of the hybrid powertrain, including battery power limits and response limits of the engine14, transmission10, and first and second electric machines56and72. The strategic optimization control scheme310is preferably executed by the HCP5during each 100 ms loop cycle and each 25 ms loop cycle.

The outputs of the strategic optimization control scheme310are used in a shift execution and engine start/stop control scheme (‘Shift Execution and Engine Start/Stop’)320to command changes in the operation of the transmission10(‘Transmission Commands’) including changing the operating range state. This includes commanding execution of a change in the operating range state if the preferred operating range state is different from the present operating range state by commanding changes in application of one or more of the clutches C170, C262, C373, and C475and other commands. The present operating range state (‘Hybrid Range State Actual’) and an input speed profile (‘Ni_Prof’) can be determined. The input speed profile is an estimate of an upcoming time-rate change in the input speed and preferably comprises a scalar parametric value that is a targeted input speed for the forthcoming loop cycle, based upon the engine operating commands and the operator torque request during a transition in the operating range state of the transmission.

A tactical control scheme (‘Tactical Control and Operation’)330is repeatedly executed during one of the control loop cycles to determine engine commands (‘Engine Commands’) for operating the engine14, including a preferred input torque from the engine14to the transmission10based upon the output speed, the input speed, and the operator torque request and the present operating range state for the transmission. The engine commands also include engine states including one of an all-cylinder state and a cylinder deactivation state wherein a portion of the engine cylinders are deactivated and unfueled, and engine states including one of a fueled state and a fuel cutoff state.

A clutch torque (‘Tcl’) for each of the clutches C170, C262, C373, and C475is estimated in the TCM17, including the presently applied clutches and the non-applied clutches, and a present engine input torque (‘Ti’) reacting with the input member12is determined in the ECM23. A motor torque control scheme (‘Output and Motor Torque Determination’)340is executed to determine the preferred output torque from the powertrain (‘To_cmd’), which includes motor torque commands (‘TA’, ‘TB’) for controlling the first and second electric machines56and72in this embodiment. The preferred output torque is based upon the estimated clutch torque(s) for each of the clutches, the present input torque from the engine14, the present operating range state, the input speed, the operator torque request, and the input speed profile. The first and second electric machines56and72are controlled through the TPIM19to meet the preferred motor torque commands based upon the preferred output torque. The motor torque control scheme340includes algorithmic code which is regularly executed during the 6.25 ms and 12.5 ms loop cycles to determine the preferred motor torque commands.

The hybrid powertrain is controlled to transfer the output torque to the output member64and thence to the driveline90to generate tractive torque at wheel(s)93to forwardly propel the vehicle in response to the operator input to the accelerator pedal113when the operator selected position of the transmission gear selector114commands operation of the vehicle in the forward direction. Similarly, the hybrid powertrain is controlled to transfer the output torque to the output member64and thence to the driveline90to generate tractive torque at wheel(s)93to propel the vehicle in a reverse direction in response to the operator input to the accelerator pedal113when the operator selected position of the transmission gear selector114commands operation of the vehicle in the reverse direction. Preferably, propelling the vehicle results in vehicle acceleration so long as the output torque is sufficient to overcome external loads on the vehicle, e.g., due to road grade, aerodynamic loads, and other loads.

The BrCM22commands the friction brakes on the wheels93to apply braking force and generates a command for the transmission10to create a negative output torque which reacts with the driveline90in response to a net operator input to the brake pedal112and the accelerator pedal113. Preferably the applied braking force and the negative output torque can decelerate and stop the vehicle so long as they are sufficient to overcome vehicle kinetic power at wheel(s)93. The negative output torque reacts with the driveline90, thus transferring torque to the electro-mechanical transmission10and the engine14. The negative output torque reacted through the electro-mechanical transmission10can be transferred to the first and second electric machines56and72to generate electric power for storage in the ESD74.

The operator inputs to the accelerator pedal113and the brake pedal112comprise individually determinable operator torque request inputs including an immediate accelerator output torque request (‘Output Torque Request Accel Immed’), a predicted accelerator output torque request (‘Output Torque Request Accel Prdtd’), an immediate brake output torque request (‘Output Torque Request Brake Immed’), a predicted brake output torque request (‘Output Torque Request Brake Prdtd’) and an axle torque response type (‘Axle Torque Response Type’). As used herein, the term ‘accelerator’ refers to an operator request for forward propulsion preferably resulting in increasing vehicle speed over the present vehicle speed, when the operator selected position of the transmission gear selector114commands operation of the vehicle in the forward direction. The terms ‘deceleration’ and ‘brake’ refer to an operator request preferably resulting in decreasing vehicle speed from the present vehicle speed. The immediate accelerator output torque request, the predicted accelerator output torque request, the immediate brake output torque request, the predicted brake output torque request, and the axle torque response type are individual inputs to the control system including to the tactical control scheme330.

The immediate accelerator output torque request is determined based upon a presently occurring operator input to the accelerator pedal113, and comprises a request to generate an immediate output torque at the output member64preferably to accelerate the vehicle. The immediate accelerator output torque request is unshaped, but can be shaped by events that affect vehicle operation outside the powertrain control. Such events include vehicle level interruptions in the powertrain control for antilock braking, traction control and vehicle stability control, which can be used to unshape or rate-limit the immediate accelerator output torque request.

The predicted accelerator output torque request is determined based upon the operator input to the accelerator pedal113and comprises an optimum or preferred output torque at the output member64. The predicted accelerator output torque request is preferably equal to the immediate accelerator output torque request during normal operating conditions, e.g., when any one of antilock braking, traction control, or vehicle stability is not being commanded. When any one of antilock braking, traction control or vehicle stability is being commanded the predicted accelerator output torque request remains the preferred output torque with the immediate accelerator output torque request being decreased in response to output torque commands related to the antilock braking, traction control, or vehicle stability control.

Blended brake torque includes a combination of the friction braking torque generated at the wheels93and the output torque generated at the output member64which reacts with the driveline90to decelerate the vehicle in response to the operator input to the brake pedal112.

The immediate brake output torque request is determined based upon a presently occurring operator input to the brake pedal112, and comprises a request to generate an immediate output torque at the output member64to effect a reactive torque with the driveline90which preferably decelerates the vehicle. The immediate brake output torque request is determined based upon the operator input to the brake pedal112and the control signal to control the friction brakes to generate friction braking torque.

The predicted brake output torque request comprises an optimum or preferred brake output torque at the output member64in response to an operator input to the brake pedal112subject to a maximum brake output torque generated at the output member64allowable regardless of the operator input to the brake pedal112. In one embodiment the maximum brake output torque generated at the output member64is limited to −0.2 g. The predicted brake output torque request can be phased out to zero when vehicle speed approaches zero regardless of the operator input to the brake pedal112. As desired by a user, there can be operating conditions under which the predicted brake output torque request is set to zero, e.g., when the operator setting to the transmission gear selector114is set to a reverse gear, and when a transfer case (not shown) is set to a four-wheel drive low range. The operating conditions whereat the predicted brake output torque request is set to zero are those in which blended braking is not preferred due to vehicle operating factors.

The axle torque response type comprises an input state for shaping and rate-limiting the output torque response through the first and second electric machines56and72. The input state for the axle torque response type can be an active state, preferably comprising one of a pleasability limited state a maximum range state, and an inactive state. When the commanded axle torque response type is the active state, the output torque command is the immediate output torque. Preferably the torque response for this response type is as fast as possible.

The predicted accelerator output torque request and the predicted brake output torque request are input to the strategic optimization control scheme (‘Strategic Control’)310. The strategic optimization control scheme310determines a desired operating range state for the transmission10(‘Hybrid Range State Des’) and a desired input speed from the engine14to the transmission10(‘Ni Des’), which comprise inputs to the shift execution and engine start/stop control scheme (‘Shift Execution and Engine Start/Stop’)320.

A change in the input torque from the engine14which reacts with the input member from the transmission10can be effected by changing mass of intake air to the engine14by controlling position of an engine throttle utilizing an electronic throttle control system (not shown), including opening the engine throttle to increase engine torque and closing the engine throttle to decrease engine torque. Changes in the input torque from the engine14can be effected by adjusting ignition timing, including retarding spark timing from a mean-best-torque spark timing to decrease engine torque. The engine state can be changed between the engine-off state and the engine-on state to effect a change in the input torque. The engine state can be changed between the all-cylinder state and the cylinder deactivation state, wherein a portion of the engine cylinders are unfueled. The engine state can be changed by selectively operating the engine14in one of the fueled state and the fuel cutoff state wherein the engine is rotating and unfueled. Executing a shift in the transmission10from a first operating range state to a second operating range state can be commanded and achieved by selectively applying and deactivating the clutches C170, C262, C373, and C475.

FIG. 4details the tactical control scheme (‘Tactical Control and Operation’)330for controlling operation of the engine14, described with reference to the hybrid powertrain system ofFIGS. 1 and 2and the control system architecture ofFIG. 3. The tactical control scheme330includes a tactical optimization control path350and a system constraints control path360which are preferably executed concurrently. The outputs of the tactical optimization control path350are input to an engine state control scheme370. The outputs of the engine state control scheme370and the system constraints control path360are input to an engine response type determination scheme (‘Engine Response Type Determination’)380for controlling the engine state, the immediate engine torque request and the predicted engine torque request.

The operating point of the engine14is described in terms of the input torque and input speed that can be achieved by controlling mass of intake air to the engine14when the engine14comprises a spark-ignition engine by controlling position of an engine throttle (not shown) utilizing an electronic throttle control device (not shown). This includes opening the throttle to increase the engine input speed and torque output and closing the throttle to decrease the engine input speed and torque. The engine operating point can be achieved by adjusting ignition timing, generally by retarding spark timing from a mean-best-torque spark timing to decrease engine torque.

When the engine14comprises a compression-ignition engine, the operating point of the engine14can be achieved by controlling the mass of injected fuel, and adjusted by retarding injection timing from a mean-best-torque injection timing to decrease engine torque.

The engine operating point can be achieved by changing the engine state between the engine-off state and the engine-on state. The engine operating point can be achieved by controlling the engine state between the all-cylinder state and the cylinder deactivation state, wherein a portion of the engine cylinders are unfueled and the engine valves are deactivated. The engine state can include the fuel cutoff state wherein the engine is rotating and unfueled to effect engine braking.

The tactical optimization control path350acts on substantially steady state inputs to select a preferred engine state and determine a preferred input torque from the engine14to the transmission10. The inputs originate in the shift execution and engine state control scheme320. The tactical optimization control path350includes an optimization scheme (‘Tactical Optimization’)354to determine preferred input torques for operating the engine14in the all-cylinder state (‘Input Torque Full’), in the cylinder deactivation state (‘Input Torque Deac’), the all-cylinder state with fuel cutoff (‘Input Torque Full FCO’), in the cylinder deactivation state with fuel cutoff (‘Input Torque Deac FCO’), and a preferred engine state (‘Preferred Engine State’). Inputs to the optimization scheme354include a lead operating range state of the transmission10(‘Lead Hybrid Range State’) a predicted lead input acceleration profile (‘Lead Input Acceleration Profile Predicted’), a predicted range of clutch reactive torques (‘Predicted Clutch Reactive Torque Min/Max’) for each presently applied clutch, predicted battery power limits (‘Predicted Battery Power Limits’) and predicted output torque requests for acceleration (‘Output Torque Request Accel Prdtd’) and braking (‘Output Torque Request Brake Prdtd’). The predicted output torque requests for acceleration and braking are combined and shaped with the axle torque response type through a predicted output torque shaping filter352to yield a predicted net output torque request (‘To Net Prdtd’) and a predicted accelerator output torque request (‘To Accel Prdtd’), which are inputs to the optimization scheme354. The lead operating range state of the transmission10comprises a time-shifted lead of the operating range state of the transmission10to accommodate a response time lag between a commanded change in the operating range state and a measured change in the operating range state. The predicted lead input acceleration profile comprises a time-shifted lead of the predicted input acceleration profile of the input member12to accommodate a response time lag between a commanded change in the predicted input acceleration profile and a measured change in the predicted input acceleration profile. The optimization scheme354determines costs for operating the engine14in the engine states, which comprise operating the engine fueled and in the all-cylinder state (‘PCOST FULL FUEL’), operating the engine unfueled and in the all-cylinder state (‘PCOST FULL FCO’), operating the engine fueled and in cylinder deactivation state (‘PCOST DEAC FUEL’), and operating the engine unfueled and in the cylinder deactivation state (‘PCOST DEAC FCO’). The aforementioned costs for operating the engine14are input to a stabilization analysis scheme (‘Stabilization and Arbitration’)356along with the actual engine state (‘Actual Engine State’) and an allowable or permissible engine state (‘Engine State Allowed’) to select one of the engine states as the preferred engine state (‘Preferred Engine State’).

The preferred input torques for operating the engine14in the all-cylinder state and in the cylinder deactivation state with and without fuel cutoff are input to an engine torque conversion calculator (‘Engine Torque Conversion’)355and converted to preferred engine torques in the all-cylinder state and in the cylinder deactivation state (‘Engine Torque Full’) and (‘Engine Torque Deac’) and with fuel cutoff in the all-cylinder state and in the cylinder deactivation state (‘Engine Torque Full FCO’) and (‘Engine Torque Deac FCO’) respectively, by taking into account parasitic and other loads introduced between the engine14and the transmission10. The preferred engine torques for operation in the all-cylinder state and in the cylinder deactivation state and the preferred engine state comprise inputs to the engine state control scheme370.

The costs for operating the engine14include operating costs which are generally determined based upon factors that include vehicle driveability, fuel economy, emissions, and battery usage. Costs are assigned and associated with fuel and electrical power consumption and are associated with a specific operating points of the hybrid powertrain. Lower operating costs are generally associated with lower fuel consumption at high conversion efficiencies, lower battery power usage, and lower emissions for each engine speed/load operating point, and take into account the present state of the engine14.

The preferred engine state and the preferred engine torques in the all-cylinder state and in the cylinder deactivation state are input to the engine state control scheme370, which includes an engine state machine (‘Engine State Machine’)372. The engine state machine372determines a target engine torque (‘Target Engine Torque’) and a target engine state (‘Target Engine State’) based upon the preferred engine torques and the preferred engine state. The target engine torque and the target engine state are input to a transition filter (‘Transition Filtering’)374which monitors any commanded transition in the engine state and filters the target engine torque to provide a filtered target engine torque (‘Filtered Target Engine Torque’). The engine state machine372outputs a command that indicates selection of one of the cylinder deactivation state and the all-cylinder state (‘DEAC Selected’) and indicates selection of one of the engine-on state and the deceleration fuel cutoff state (‘FCO Selected’).

The selection of one of the cylinder deactivation state and the all-cylinder state and the selection of one of the engine-on state and the deceleration fuel cutoff state, the filtered target engine torque, and the minimum and maximum engine torques are input to the engine response type determination scheme380.

The system constraints control path360determines constraints on the input torque, comprising minimum and maximum input torques (‘Input Torque Hybrid Minimum’ and ‘Input Torque Hybrid Maximum’) that can be reacted by the transmission10. The minimum and maximum input torques are determined based upon constraints to the transmission10and the first and second electric machines56and72, including clutch torques and battery power limits, which affect the capacity of the transmission10to react input torque during the current loop cycle. Inputs to the system constraints control path360include the immediate output torque request as measured by the accelerator pedal113(‘Output Torque Request Accel Immed’) and the immediate output torque request as measured by the brake pedal112(‘Output Torque Request Brake Immed’) which are combined and shaped with the axle torque response type through an immediate output torque shaping filter (‘Immediate Output Torque Shaping’)362to yield a net immediate output torque (‘To Net Immed’) and an immediate accelerator output torque (‘To Accel Immed’). The net immediate output torque and the immediate accelerator output torque are inputs to a constraints scheme (‘Output and Input Torque Constraints’)364. Other inputs to the constraints scheme364include the lead operating range state of the transmission10, an immediate lead input acceleration profile (‘Lead Input Acceleration Profile Immed’), a lead immediate clutch reactive torque range (‘Lead Immediate Clutch Reactive Torque Min/Max’) for each presently applied clutch, and the available battery power (‘Battery Power Limits’) comprising the range PBAT—MINto PBAT—MAX. The immediate lead input acceleration profile comprises a time-shifted lead of the immediate input acceleration profile of the input member12to accommodate a response time lag between a commanded change in the immediate input acceleration profile and a measured change in the immediate input acceleration profile. The lead immediate clutch reactive torque range comprises a time-shifted lead of the immediate clutch reactive torque range of the clutches to accommodate a response time lag between a commanded change in the immediate clutch torque range and a measured change in the immediate clutch reactive torque range. The constraints scheme364determines an output torque range for the transmission10, and then determines the minimum and maximum allowable input torques (‘Input Torque Hybrid Minimum’ and ‘Input Torque Hybrid Maximum’ respectively) that can be reacted by the transmission10based upon the aforementioned inputs. The minimum and maximum allowable input torques can change during ongoing operation, due to changes in the aforementioned inputs, including increasing energy recovery through electric power regeneration through the transmission14and first and second electric machines56and72.

The minimum and maximum allowable input torques are input to the engine torque conversion calculator355and converted to minimum and maximum engine torques (‘Engine Torque Hybrid Minimum’ and ‘Engine Torque Hybrid Maximum’ respectively), by taking into account parasitic and other loads introduced between the engine14and the transmission10.

The filtered target engine torque, the output of the engine state machine372and the minimum and maximum engine torques are input to the engine response type determination scheme380, which inputs the engine commands to the ECM23for controlling the engine state, the immediate engine torque request and the predicted engine torque request. The engine commands include an immediate engine torque request (‘Engine Torque Request Immed’) and a predicted engine torque request (‘Engine Torque Request Prdtd’) that can be determined based upon the filtered target engine torque. Other commands control the engine state to one of the engine fueled state and the deceleration fuel cutoff state (‘FCO Request’) and to one of the cylinder deactivation state and the all-cylinder state (‘DEAC Request’). Another output comprises an engine response type (‘Engine Response Type’). When the filtered target engine torque is within the range between the minimum and maximum engine torques, the engine response type is inactive. When the filtered target engine torque is outside the constraints of the minimum and maximum engine torques (‘Engine Torque Hybrid Minimum’) and (‘Engine Torque Hybrid Maximum’) the engine response type is active, indicating a need for an immediate change in the engine torque, e.g., through engine spark control and retard to change the engine torque and the input torque to fall within the constraints of the minimum and maximum engine torques.

FIG. 5depicts the engine state control scheme370including the engine state machine372and the transition filter374. The preferred engine state (‘Preferred Engine State’) is input to the engine state machine372. The engine state machine372selects and outputs a target engine state (‘Target Engine State’) and a target engine torque (‘Target Engine Torque’) based on the preferred engine state.

FIG. 6shows permissible states of an exemplary state machine including a plurality of main states (‘State0’, ‘State1’, ‘State2’, and ‘State3’) and a plurality of transition states (T4, T5, T6, T7, T8, T9, T12, and T13). In the embodiment the main states and transition states preferably correspond to engine states. As applied to the embodiment described herein, the main states include a first main state corresponding to engine operation in the fueled, all-cylinder engine state (hereafter ‘State0’), a second main state corresponding to engine operation in the all-cylinder engine state with fuel cutoff (hereafter, ‘State1’), a third main state corresponding to the cylinder deactivation engine state (hereafter, ‘State2’), and a fourth main state corresponding to the engine in the cylinder deactivation engine state with fuel cutoff (hereafter, ‘State3’). Other inputs to the engine state machine372include the engine torques from the optimization scheme354for each of the engine states converted from the corresponding input torques for each of the main states. The engine state machine372inputs the preferred engine torque corresponding to state0(‘Engine Torque Full’), the engine torque corresponding to state1(‘Engine Torque Full FCO’), the preferred engine torque corresponding to state2(‘Engine Torque Deac’), and the engine torque corresponding to state3(‘Engine Torque Deac FCO’). The engine state machine372further inputs state enablement information (‘Enable Bits’), the present or actual engine state (‘Actual Engine State’) and the state of the transition (‘Transition Completed’).

The transition filter374generates a signal comprising the state of the transition to indicate whether specific engine states are enabled, thus permitting transition thereto. The transition filter374includes information indicating whether the transition to the target engine state can be completed.

The engine state machine372determines and outputs the target engine state (‘Target Engine State’) and sends signals indicating selection of the cylinder deactivation state (‘DEAC Selected’) and indicating selection of the fuel cutoff state (‘FCO Selected’). Further, the engine state machine372determines and outputs the target engine torque (‘Target Engine Torque’) comprising the engine torque corresponding to the target engine state. This includes an upcoming transition engine state and a corresponding transition engine torque following a transition path determined by the state machine.

The engine state machine372includes the transition paths, e.g., as shown inFIG. 6, for controlling transitions between the main states including the transition states between the main states. The transition paths include a transition path from the fueled, all-cylinder state to the fueled, cylinder deactivation state (hereafter “state T4”), a transition path from the fueled, cylinder deactivation state to the fueled, all-cylinder state (hereafter “state T5”), a transition path from the fueled, all-cylinder state to the fuel-cutoff, all-cylinder state (hereafter “state T6”), a transition path from the fuel-cutoff, all-cylinder state to the fueled, all-cylinder state (hereafter “state T7”), a transition path from the fueled, cylinder deactivation state to the fuel-cutoff, cylinder deactivation state (hereafter “state T8”), a transition path from the fuel-cutoff, cylinder deactivation state to the fueled, cylinder deactivation state (hereafter “state T9”), a transition path from state T8to the fuel-cutoff, all-cylinder state (hereafter “state T12”), and a transition path from state T6to the fuel-cutoff, cylinder deactivation state (hereafter “state T13”).

The engine state machine372selects a preferred transition path based on the present engine state and the target engine state. If the enablement information indicates that one of the transition states of the preferred transition path is not available, the engine state machine372can determine an alternate transition path. For example, the engine state machine372can determine a preferred transition path between state3and state0comprising transitioning from state3to state T9, then to state2, then to state T5, and then to state0. However, if the enablement information indicates that cylinder deactivation is unavailable, the engine state machine372can determine an alternate transition path comprising transitioning from state3to state T5, then to state0.

The engine state machine372continuously monitors the preferred engine state when in a transition state, and can thereby determine a transition path that connects directly between two transition states. For example, if the engine state machine372detects a change in the preferred engine state to state0when the state is the transition state T4, the engine state machine determines a transition path to transition from state T4to state T5, and from state T5to state0.

The transition filter374includes a first order, low pass filter to determine and manage the engine torque during an engine state transition. The filter can be described by Eq. 1:

y⁡(t)=[u⁡(t)-y⁡(t-1)]·dTT+y⁡(t-1)[1]
wherein y is the filtered target engine torque,

u is the target engine torque

t is elapsed time

dT is a sample time, and

T is a filter time constant.

The filter time constant T is determined utilizing the state of the state machine372, the target engine torque, the preferred engine state, the filtered target engine torque and the actual engine state. By utilizing inputs to determine the filter time constant T, a low pass filter of transition filter374provides a change in the input torque over a minimum transition time without causing sudden undesired torque changes when transitioning between states.

An incremental change in the engine torque can be described as y(t)−y(t−1) for the low pass filter according to Eq. 1, shown in Eq. 2:

To account for a decrease in the incremental change in the engine torque as the filtered target engine torque y(t−1) approaches the target engine torque u(t), the low pass filter deviates from a standard low pass filter by providing a minimum incremental change in the engine torque. This minimum incremental change causes a transition from a low pass filter response to a ramp as y(t) approaches u(t), resulting in shorter transition times.

The transition filter374adjusts incrementally to the target engine torque and outputs the filtered target engine torque for controlling operation of the engine14. The main state enablement information comprising ‘Transition Complete’ indicates that the filtered target engine torque substantially coincides with the target engine torque and that therefore a transition from the present engine state to the target engine state can take place. While the engine state machine372is in one of the transition states T4, T5, T6, T7, T8, T9, T12, T13, the selections of the target engine state and of the target engine torque are coordinated.

When the engine state machine372is one of the transition states T4and T13, the transition filter374incrementally adjusts the engine torque to the preferred engine torque of states2and3, respectively, prior to transitioning the engine from the all-cylinder state to the cylinder deactivation state. When the state machine372is in one of the transition states T5and T12, the state machine372first transitions the target engine state from the cylinder deactivation state to the all-cylinder state and then adjusts the engine torque to the preferred engine torque of main states0and1respectively.

When the engine state machine372is in one of the transition states T6and T8, the transition filter374incrementally adjusts filtered target engine torque to the preferred engine torque of states1and3respectively prior to transitioning the engine from the fueled engine state to the fuel cutoff state. When the state machine is in one of the transition states T7and T9, the state machine372first transitions the target engine state from the fuel cutoff state to the fueled state and then adjusts the filtered target engine torque to the preferred engine torque of the main states0and2respectively.

FIG. 7shows exemplary data comprising engine state and engine torque for the system described herein, depicting engine state transitions and corresponding engine torque. A first graph600depicts the state602output from by the state machine372and an engine state604being one of the all-cylinder state and the cylinder deactivation state over a time period605.FIG. 7shows graph620depicting the target engine torque622output from the state machine372and the filtered target engine torque624output from the transition filter372over the time period605corresponding to the state602.

The engine state machine372determines a state602comprising state T4in response to a commanded change in the preferred engine state from state0to state2. The state602transitions from main state0to state T4. The filtered torque622is incrementally adjusted using Eqs. 1-2 above to transition from the target engine torque620of the preferred engine torque of main state0to the target engine torque620of the preferred engine torque of main state2. When the filtered target engine torque622meets the preferred engine torque of state2, the transition to main state enablement information signals the engine state machine372to transition to state2. Due to the delays in the communication between the HCP5and the ECM23and due to delays in changing the operation state of the engine14, the actual cylinder deactivation can be delayed 100-200 milliseconds after transitioning into main state2and the output of the cylinder deactivation state command by the engine state machine372.

When the engine state machine372subsequently determines a state602equal to state T5(not shown) in response to a change in the preferred engine state from state2to state0. The state602transitions from state2to state T5. In state T5, the transition from cylinder deactivation state to all cylinder state is commanded and achieved after a delay of 100-200 milliseconds. The filtered torque622is incrementally adjusted using Eqs. 1-2 above to transition between the target engine torque620of the preferred engine torque of state2and the target engine torque620of the preferred torque of state0. When the filtered target engine torque622substantially coincides with the preferred engine torque for state0, the transition to main state enablement information signals the engine state machine372to transition from T5to state0.