# Patent

## Title
Control of engine torque during upshift and downshift torque phase for a hybrid powertrain system

## Abstract

A powertrain includes an electro-mechanical transmission mechanically-operatively coupled to an internal combustion engine and an electric machine adapted to selectively transmit mechanical power to an output member through selective application of a plurality of clutches. A method for controlling the powertrain includes commanding a shift from a fixed gear operating range state to a second operating range state, commanding decreased reactive torque through an off-going clutch during a torque phase of said commanded shift, and decreasing said reactive torque through said off-going clutch through control of engine input torque.

## Background
CROSS REFERENCE TO RELATED APPLICATIONS
This application claims the benefit of U.S. Provisional Application No. 60/985,254 filed on Nov. 4, 2007 which is hereby incorporated herein by reference.


TECHNICAL FIELD
This disclosure pertains to control systems for electromechanical transmissions.
BACKGROUND
The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
Known powertrain architectures include torque-generative devices, including internal combustion engines and electric machines, which transmit torque through a transmission device to an output member. One exemplary powertrain includes a two-mode, compound-split, electromechanical transmission which utilizes an input member for receiving motive 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. Electric machines, operative as motors or generators, generate an input torque to the transmission, independently of an input torque from the internal combustion engine. The electric machines may transform vehicle kinetic energy, transmitted through the vehicle driveline, to electrical energy that is storable in an electrical energy storage device. A control system monitors various inputs from the vehicle and the operator and provides operational control of the powertrain, including controlling transmission operating range state and gear shifting, controlling the torque-generative devices, and regulating the electrical power interchange among the electrical energy storage device and the electric machines to manage outputs of the transmission, including torque and rotational speed.
Transmissions within a hybrid powertrain, as described above, serve a number of functions by transmitting and manipulating torque in order to provide torque to an output member. In order to serve the particular function required, the transmission selects between a number of operating range states or configurations internal to the transmission defining the transfer of torque through the transmission. Known transmissions utilize operating range states including fixed gear states or states with a defined gear ratio. For example, a transmission can utilize four sequentially arranged fixed gear states and allow selection between the four gear states in order to provide output torque through a wide range of output member speeds. Additively or alternatively, known transmissions also allow for continuously variable operating range states or mode states, enabled for instance through the use of a planetary gear set, wherein the gear ratio provided by the transmission can be varied across a range in order to modulate the output speed and output torque provided by a particular set of inputs. Additionally, transmissions can operate in a neutral state, ceasing all torque from being transmitted through the transmission. Additionally, transmissions can operate in a reverse mode, accepting input torque in a particular rotational direction used for normal forward operation and reversing the direction of rotation of the output member. Through selection of different operating range states, transmissions can provide a range of outputs for a given input.
Operation of the above devices within a hybrid powertrain vehicle require management of numerous torque bearing shafts or devices representing connections to the above mentioned engine, electrical machines, and driveline. Input torque from the engine and input torque from the electric machine or electric machines can be applied individually or cooperatively to provide output torque. However, changes in output torque required from the transmission, for instance, due to a change in operator pedal position or due to an operating range state shift, must be handled smoothly. Particularly difficult to manage are input torques, applied simultaneously to a transmission, with different reaction times to a control input. Based upon a single control input, the various devices can change respective input torques at different times, causing increased abrupt changes to the overall torque applied through the transmission. Abrupt or uncoordinated changes to the various input torques applied to a transmission can cause a perceptible change in acceleration or jerk in the vehicle, which can adversely affect vehicle drivability.
Various control schemes and operational connections between the various aforementioned components of the hybrid drive system are known, and the control system must be able to engage to and disengage the various components from the transmission in order to perform the functions of the hybrid powertrain system. Engagement and disengagement are known to be accomplished within the transmission by employing selectively operable clutches. Clutches are devices well known in the art for engaging and disengaging shafts including the management of rotational velocity and torque differences between the shafts. Engagement or locking, disengagement or unlocking, operation while engaged or locked operation, and operation while disengaged or unlocked operation are all clutch states that must be managed in order for the vehicle to operate properly and smoothly.
Clutches are known in a variety of designs and control methods. One known type of clutch is a mechanical clutch operating by separating or joining two connective surfaces, for instance, clutch plates, operating, when joined, to apply frictional torque to each other. One control method for operating such a mechanical clutch includes applying a hydraulic control system implementing fluidic pressures transmitted through hydraulic lines to exert or release clamping force between the two connective surfaces. Operated thusly, the clutch is not operated in a binary manner, but rather is capable of a range of engagement states, from fully disengaged, to synchronized but not engaged, to engaged but with only minimal clamping force, to engaged with some maximum clamping force. Clamping force applied to the clutch determines how much reactive torque the clutch can carry before the clutch slips. Variable control of clutches through modulation of clamping force allows for transition between locked and unlocked states and further allows for managing slip in a locked transmission. In addition, the maximum clamping force capable of being applied by the hydraulic lines can also vary with vehicle operating states and can be modulated based upon control strategies.
Clutches are known to be operated asynchronously, designed to accommodate some level of slip in transitions between locked and unlocked states. Other clutches are known to be operated synchronously, designed to match speeds of connective surfaces or synchronize before the connective surfaces are clamped together. This disclosure deals primarily with synchronous clutches.
Slip, or relative rotational movement between the connective surfaces of the clutch when the clutch connective surfaces are intended to be synchronized and locked, occurs whenever reactive torque applied to the clutch exceeds actual capacity torque created by applied clamping force. Slip in a transmission results in unintended loss of torque control within the transmission, results in loss of engine speed control and electric machine speed control caused by a sudden change in back-torque from the transmission, and results in sudden changes to vehicle acceleration, creating adverse affects to drivability.
Transmissions can operate with a single clutch transmitting reactive torque between inputs and an output. Transmission can operate with a plurality of clutches transmitting reactive torque between inputs and an output. Selection of operating range state depends upon the selective engagement of clutches, with different allowable combinations resulting in different operating range states.
A shift or transition from one operating range state to another operating range state involves transitioning at least one clutch state. An exemplary transition from one fixed gear state, including two clutches initially in a locked state, to another fixed gear state, including at least one different engaged clutch, involves unloading a first clutch, transitioning through a freewheeling or inertia speed phase state, and subsequently loading a second clutch. A driveline connected to a locked clutch, prior to being unloaded, is acted upon by an output torque resulting through the transmission as a result of input torques and reduction factors present in the transmission. In such a torque transmitting state, the clutch so configured during a shift is said to be in a torque phase. In a torque phase, vehicle speed and vehicle acceleration are functions of the output torque and other forces acting upon the vehicle. Unloading a clutch removes all input torque from a previously locked and synchronized clutch. In this configuration, the transmission is said to be in an inertia speed phase. Depending upon the particular configuration of the transmission, such an inertia speed phase can result in the vehicle coasting, or another loaded clutch may continue to provide output torque through the transmission while the first clutch is in the inertia speed phase. As the second clutch to be loaded is synchronized and loaded, the transmission again enters a torque phase, wherein vehicle speed and vehicle acceleration are functions of the output torque and other forces acting upon the vehicle. While output torque changes or interruptions due to clutch unloading and loading are a normal part of transmission operating range state shifts, orderly management of the output torque changes reduces the impact of the shifts to drivability.
As described above, transitions in transmission operating range states involve transitioning clutches. Vehicles utilizing a plurality of clutches in various engagement states through a transition can maintain a transmission of torque through a transition in operating range state. However, engine operation and torque output may not be accommodative to the change in operating range states. As described above, transitioning a clutch designed for synchronous operation from a locked state to an unlocked state requires that all torque be removed from the clutch. If two clutches are initially locked and transmitting torque from inputs including the engine, and one clutch must be unloaded prior to a pending clutch transition, an entirety of the torque being transmitted from the inputs must be transmitted by the remaining locked clutch. The remaining locked clutch has a maximum torque capacity that can be transmitted through the clutch. Engine output is known to change slowly, and transitions in operating range state preferably include smooth output from the engine to preserve drivability and create the least perception of change to the customer through the change. A method to manage torques from inputs in a hybrid transmission upon initiation of transmission operating range state transition, preferably managing changes to torque without affecting engine output, but ultimately protecting the transmission from the occurrence of slip, would be beneficial.
SUMMARY
A powertrain includes an electromechanical transmission mechanically-operatively coupled to an internal combustion engine and an electric machine adapted to selectively transmit mechanical power to an output member through selective application of a plurality of clutches. A method for controlling the powertrain includes commanding a shift from a fixed gear operating range state to a second operating range state, commanding decreased reactive torque through an off-going clutch during a torque phase of said commanded shift, and decreasing said reactive torque through said off-going clutch through control of engine input torque.



BRIEF DESCRIPTION OF THE DRAWINGS
One or more embodiments will now be described, by way of example, with reference to the accompanying drawings, in which:
FIG. 1 is a schematic diagram of an exemplary powertrain comprising a two-mode, compound-split, electromechanical hybrid transmission operatively connected to an engine and first and second electric machines, in accordance with the present disclosure;
FIG. 2 is a schematic block diagram of an exemplary distributed control module system, in accordance with the present disclosure;
FIG. 3 graphically depicts reaction times of exemplary hybrid powertrain components to changes in torque request, in accordance with the present disclosure;
FIG. 4 demonstrates gear transition relationships for an exemplary hybrid powertrain transmission, in particular as described in the exemplary embodiment of FIG. 1 and Table 1, in accordance with the present disclosure;
FIGS. 5-7 depict exemplary processes combining to accomplish an exemplary transmission shift, in accordance with the present disclosure;
FIG. 5 is a graphical representation of torque terms associated with a clutch through an exemplary transitional unlocking state, in accordance with the present disclosure;
FIG. 6 is a graphical representation of torque terms associated with a clutch through an exemplary transitional locking state, in accordance with the present disclosure;
FIG. 7 is a graphical representation of terms describing an exemplary inertia speed phase of a transmission, in accordance with the present disclosure;
FIG. 8 is a graphical representation of an instance where a systemic restraint is imposed upon an immediate control signal, temporarily overriding max\min values set by the control signal, in accordance with the present disclosure;
FIG. 9 shows an exemplary control system architecture for controlling and managing torque and power flow in a powertrain system having multiple torque generative devices and residing in control modules in the form of executable algorithms and calibrations, in accordance with the present disclosure;
FIG. 10 is a schematic diagram exemplifying data flow through a shift execution, describing more detail exemplary execution of the control system architecture of FIG. 9 in greater detail, in accordance with the present disclosure;
FIG. 11 is a schematic diagram exemplifying signal flow in a tactical control scheme for controlling operation of an engine, described with reference to the hybrid powertrain system of FIGS. 1 and 2 and the control system architecture of FIG. 9, in accordance with the present disclosure;
FIG. 12 is a graphical representation of terms describing an exemplary inertia speed phase of a transmission, including minimum and maximum engine torques, in accordance with the present disclosure; and
FIG. 13 is graphical representation of terms describing an exemplary inertia speed phase of a transmission, including minimum and maximum engine torques acting to change engine output, in accordance with the present disclosure.



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 2 depict an exemplary electro-mechanical hybrid powertrain. The exemplary electromechanical hybrid powertrain in accordance with the present disclosure is depicted in FIG. 1, comprising a two-mode, compound-split, electromechanical hybrid transmission 10 operatively connected to an engine 14 and first and second electric machines (‘MG-A’) 56 and (‘MG-B’) 72. The engine 14 and first and second electric machines 56 and 72 each generate power which can be transmitted to the transmission 10. The power generated by the engine 14 and the first and second electric machines 56 and 72 and transmitted to the transmission 10 is described in terms of input torques, referred to herein as TI, TA, and TB respectively, and speed, referred to herein as NI, NA, and NB, respectively.
The exemplary engine 14 comprises a multi-cylinder internal combustion engine selectively operative in several states to transmit torque to the transmission 10 via an input shaft 12, and can be either a spark-ignition or a compression-ignition engine. The engine 14 includes a crankshaft (not shown) operatively coupled to the input shaft 12 of the transmission 10. A rotational speed sensor 11 monitors rotational speed of the input shaft 12. Power output from the engine 14, comprising rotational speed and output torque, can differ from the input speed, NI, and the input torque, TI, to the transmission 10 due to placement of torque-consuming components on the input shaft 12 between the engine 14 and the transmission 10, e.g., a hydraulic pump (not shown) and/or a torque management device (not shown).
The exemplary transmission 10 comprises three planetary-gear sets 24, 26 and 28, and four selectively engageable torque-transmitting devices, i.e., clutches C1 70, C2 62, C3 73, and C4 75. 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 circuit 42, preferably controlled by a transmission control module (hereafter ‘TCM’) 17, is operative to control clutch states. Clutches C2 62 and C4 75 preferably comprise hydraulically-applied rotating friction clutches. Clutches C1 70 and C3 73 preferably comprise hydraulically-controlled stationary devices that can be selectively grounded to a transmission case 68. Each of the clutches C1 70, C2 62, C3 73, and C4 75 is preferably hydraulically applied, selectively receiving pressurized hydraulic fluid via the hydraulic control circuit 42.
The first and second electric machines 56 and 72 preferably comprise three-phase AC machines, each including a stator (not shown) and a rotor (not shown), and respective resolvers 80 and 82. The motor stator for each machine is grounded to an outer portion of the transmission case 68, and includes a stator core with coiled electrical windings extending therefrom. The rotor for the first electric machine 56 is supported on a hub plate gear that is operatively attached to shaft 60 via the second planetary gear set 26. The rotor for the second electric machine 72 is fixedly attached to a sleeve shaft hub 66.
Each of the resolvers 80 and 82 preferably comprises a variable reluctance device including a resolver stator (not shown) and a resolver rotor (not shown). The resolvers 80 and 82 are appropriately positioned and assembled on respective ones of the first and second electric machines 56 and 72. Stators of respective ones of the resolvers 80 and 82 are operatively connected to one of the stators for the first and second electric machines 56 and 72. The resolver rotors are operatively connected to the rotor for the corresponding first and second electric machines 56 and 72. Each of the resolvers 80 and 82 is 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 machines 56 and 72. Additionally, the signals output from the resolvers 80 and 82 are interpreted to provide the rotational speeds for first and second electric machines 56 and 72, i.e., NA and NB, respectively.
The transmission 10 includes an output member 64, e.g. a shaft, which is operably connected to a driveline 90 for a vehicle (not shown), to provide output power, e.g., to vehicle wheels 93, one of which is shown in FIG. 1. The output power is characterized in terms of an output rotational speed, NO and an output torque, TO. A transmission output speed sensor 84 monitors rotational speed and rotational direction of the output member 64. Each of the vehicle wheels 93, is preferably equipped with a sensor 94 adapted to monitor wheel speed, VSS-WHL, the output of which is monitored by a control module of a distributed control module system described with respect to FIG. 2, to determine vehicle speed, and absolute and relative wheel speeds for braking control, traction control, and vehicle acceleration management.
The input torques from the engine 14 and the first and second electric machines 56 and 72 (TI, TA, and TB respectively) are generated as a result of energy conversion from fuel or electrical potential stored in an electrical energy storage device (hereafter ‘ESD’) 74. The ESD 74 is high voltage DC-coupled to the TPIM 19 via DC transfer conductors 27. The transfer conductors 27 include a contactor switch 38. When the contactor switch 38 is closed, under normal operation, electric current can flow between the ESD 74 and the TPIM 19. When the contactor switch 38 is opened electric current flow between the ESD 74 and the TPIM 19 is interrupted. The TPIM 19 transmits electrical power to and from the first electric machine 56 by transfer conductors 29, and the TPIM 19 similarly transmits electrical power to and from the second electric machine 72 by transfer conductors 31, in response to torque requests to the first and second electric machines 56 and 72 to achieve the input torques TA and TB. Electrical current is transmitted to and from the ESD 74 in accordance with whether the ESD 74 is being charged or discharged.
The TPIM 19 includes the pair of power inverters (not shown) and respective electric machine control modules (not shown) configured to receive the torque requests and control inverter states therefrom for providing motor drive or regeneration functionality to achieve the input torques TA and 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 ESD 74 to AC power for powering respective ones of the first and second electric machines 56 and 72, 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 conductors 27 and transform it to or from three-phase AC power, which is conducted to or from the first and second electric machines 56 and 72 for operation as motors or generators via transfer conductors 29 and 31 respectively.
FIG. 2 is 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 powertrain described in FIG. 1. The distributed control module system synthesizes pertinent information and inputs, and executes algorithms to control various actuators to achieve control objectives, including objectives related to fuel economy, emissions, performance, drivability, and protection of hardware, including batteries of ESD 74 and the first and second electric machines 56 and 72. The distributed control module system includes an engine control module (hereafter ‘ECM’) 23, the TCM 17, a battery pack control module (hereafter ‘BPCM’) 21, and the TPIM 19. A hybrid control module (hereafter ‘HCP’) 5 provides supervisory control and coordination of the ECM 23, the TCM 17, the BPCM 21, and the TPIM 19. A user interface (‘UI’) 13 is operatively connected to a plurality of devices through which a vehicle operator controls or directs operation of the electromechanical hybrid powertrain. The devices include an accelerator pedal 113 (‘AP’) from which an operator torque request is determined, an operator brake pedal 112 (‘BP’), a transmission gear selector 114 (‘PRNDL’), and a vehicle speed cruise control (not shown). The transmission gear selector 114 may have a discrete number of operator-selectable positions, including the rotational direction of the output member 64 to 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’) bus 6. The LAN bus 6 allows 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 bus 6 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 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 HCP 5 provides supervisory control of the powertrain, serving to coordinate operation of the ECM 23, TCM 17, TPIM 19, and BPCM 21. Based upon various input signals from the user interface 13 and the powertrain, including the ESD 74, the HCP 5 generates various commands, including: the operator torque request (‘TO—REQ’), a commanded output torque (‘TCMD’) to the driveline 90, an engine input torque request, clutch torques for the torque-transfer clutches C1 70, C2 62, C3 73, C4 75 of the transmission 10; and the torque requests for the first and second electric machines 56 and 72, respectively. The TCM 17 is operatively connected to the hydraulic control circuit 42 and provides various functions including monitoring various pressure sensing devices (not shown) and generating and communicating control signals to various solenoids (not shown) thereby controlling pressure switches and control valves contained within the hydraulic control circuit 42.
The ECM 23 is operatively connected to the engine 14, and functions to acquire data from sensors and control actuators of the engine 14 over a plurality of discrete lines, shown for simplicity as an aggregate bi-directional interface cable 35. The ECM 23 receives the engine input torque request from the HCP 5. The ECM 23 determines the actual engine input torque, TI, provided to the transmission 10 at that point in time based upon monitored engine speed and load, which is communicated to the HCP 5. The ECM 23 monitors input from the rotational speed sensor 11 to determine the engine input speed to the input shaft 12, which translates to the transmission input speed, NI. The ECM 23 monitors 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 pedal 113. The ECM 23 generates 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 TCM 17 is operatively connected to the transmission 10 and monitors inputs from sensors (not shown) to determine states of transmission operating parameters. The TCM 17 generates and communicates command signals to control the transmission 10, including controlling the hydraulic control circuit 42. Inputs from the TCM 17 to the HCP 5 include estimated clutch torques for each of the clutches, i.e., C1 70, C2 62, C3 73, and C4 75, and rotational output speed, No, of the output member 64. Other actuators and sensors may be used to provide additional information from the TCM 17 to the HCP 5 for control purposes. The TCM 17 monitors inputs from pressure switches (not shown) and selectively actuates pressure control solenoids (not shown) and shift solenoids (not shown) of the hydraulic control circuit 42 to selectively actuate the various clutches C1 70, C2 62, C3 73, and C4 75 to achieve various transmission operating range states, as described hereinbelow.
The BPCM 21 is signally connected to sensors (not shown) to monitor the ESD 74, including states of electrical current and voltage parameters, to provide information indicative of parametric states of the batteries of the ESD 74 to the HCP 5. 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—MIN to PBAT—MAX.
Each of the control modules ECM 23, TCM 17, TPIM 19 and BPCM 21 is 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 bus 6 and 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 powertrain. Alternatively, algorithms may be executed in response to the occurrence of an event.
The exemplary powertrain selectively operates in one of several operating range states that can be described in terms of an engine state comprising one of an engine on state (‘ON’) and an engine off state (‘OFF’), and a transmission state comprising a plurality of fixed gears and continuously variable operating modes, described with reference to Table 1, below.










TABLE 1






Engine
Transmission Operating
Applied


Description
State
Range State
Clutches



















MI_Eng_Off
OFF
EVT Mode I
C1 70



MI_Eng_On
ON
EVT Mode I
C1 70


FG1
ON
Fixed Gear Ratio 1
C1 70
C4 75


FG2
ON
Fixed Gear Ratio 2
C1 70
C2 62


MII_Eng_Off
OFF
EVT Mode II
C2 62


MII_Eng_On
ON
EVT Mode II
C2 62


FG3
ON
Fixed Gear Ratio 3
C2 62
C4 75


FG4
ON
Fixed Gear Ratio 4
C2 62
C3 73









Each of the transmission operating range states is described in the table and indicates which of the specific clutches C1 70, C2 62, C3 73, and C4 75 are applied for each of the operating range states. A first continuously variable mode, i.e., EVT Mode I, or MI, is selected by applying clutch C1 70 only in order to “ground” the outer gear member of the third planetary gear set 28. The engine state can be one of ON (‘MI_Eng_On’) or OFF (‘MI_Eng_Off’). A second continuously variable mode, i.e., EVT Mode II, or MII, is selected by applying clutch C2 62 only to connect the shaft 60 to the carrier of the third planetary gear set 28. The engine state can be one of ON (‘MII_Eng_On’) or OFF (‘MII_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 transmission 10, i.e., NI/NO, is achieved. A first fixed gear operation (‘FG1’) is selected by applying clutches C1 70 and C4 75. A second fixed gear operation (‘FG2’) is selected by applying clutches C1 70 and C2 62. A third fixed gear operation (‘FG3’) is selected by applying clutches C2 62 and C4 75. A fourth fixed gear operation (‘FG4’) is selected by applying clutches C2 62 and C3 73. The fixed ratio operation of input-to-output speed increases with increased fixed gear operation due to decreased gear ratios in the planetary gears 24, 26, and 28. The rotational speeds of the first and second electric machines 56 and 72, NA and NB respectively, are dependent on internal rotation of the mechanism as defined by the clutching and are proportional to the input speed measured at the input shaft 12.
In response to operator input via the accelerator pedal 113 and brake pedal 112 as captured by the user interface 13, the HCP 5 and one or more of the other control modules determine the commanded output torque, TCMD, intended to meet the operator torque request, TO—REQ, to be executed at the output member 64 and transmitted to the driveline 90. Final vehicle acceleration is affected by other factors including, e.g., road load, road grade, and vehicle mass. The operating range state is determined for the transmission 10 based upon a variety of operating characteristics of the powertrain. This includes the operator torque request, communicated through the accelerator pedal 113 and brake pedal 112 to the user interface 13 as previously described. The operating range state may be predicated on a powertrain torque demand caused by a command to operate the first and second electric machines 56 and 72 in an electrical energy generating mode or in a torque generating mode. The operating range state can be determined by an optimization algorithm or routine, initiated for example within a hybrid strategic control module of the HCP 5, which determines optimum system efficiency based upon operator demand for power, battery state of charge, and energy efficiencies of the engine 14 and the first and second electric machines 56 and 72. The control system manages torque inputs from the engine 14 and the first and second electric machines 56 and 72 based 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 HCP 5 monitors the torque-generative devices, and determines the power output from the transmission 10 required to achieve the desired output torque to meet the operator torque request. As should be apparent from the description above, the ESD 74 and the first and second electric machines 56 and 72 are electrically-operatively coupled for power flow therebetween. Furthermore, the engine 14, the first and second electric machines 56 and 72, and the electromechanical transmission 10 are mechanically-operatively coupled to transmit power therebetween to generate a power flow to the output member 64.
As discussed above, managing output torque in order to maintain drivability is a priority in controlling a hybrid powertrain. Any change in torque in response to a change in output torque request applied through the transmission results in a change to the output torque applied to the driveline, thereby resulting in a change in propelling force to the vehicle and a change in vehicle acceleration. The change in torque request can come from operator input, such a pedal position relating an operator torque request, automatic control changes in the vehicle, such as cruise control or other control strategy, or engine changes in response to environmental conditions, such as a vehicle experiencing an uphill or downhill grade. By controlling changes to various input torques applied to a transmission within a hybrid powertrain, abrupt changes in vehicle acceleration can be controlled and minimized in order to reduce adverse effects to drivability.
As is known by one having ordinary skill in the art, any control system includes a reaction time. Changes to a powertrain operating point, comprising the speeds and torques of the various components to the powertrain required to achieve the desired vehicle operation, are driven by changes in control signals. These control signal changes act upon the various components to the powertrain and create reactions in each according to their respective reaction times. Applied to a hybrid powertrain, any change in control signals indicating a new torque request, for instance, as driven by a change in operator torque request or as required to execute a transmission shift, creates reactions in each affected torque generating device in order to execute the required changes to respective input torques. Changes to input torque supplied from an engine are controlled by an engine torque request setting the torque generated by the engine, as controlled, for example, through an ECM. Reaction time within an engine to changes in torque request to an engine is impacted by a number of factors well known in the art, and the particulars of a change to engine operation depend heavily on the particulars of the engine employed and the mode or modes of combustion being utilized. In many circumstances, the reaction time of an engine to changes in torque request will be the longest reaction time of the components to the hybrid drive system. Reaction time within an electric machine to changes in torque request include time to activate any necessary switches, relays, or other controls and time to energize or de-energize the electric machine with the change in applied electrical power.
FIG. 3 graphically depicts reaction times of exemplary hybrid powertrain components to changes in torque request, in accordance with the present disclosure. Components to an exemplary hybrid powertrain system including an engine and two electric machines are exemplified. Torque requests and resulting changes in input torque produced by each torque generating device are illustrated. As described above, the data shows that electric machines quickly respond to changes in torque requests, whereas the engine follows changes in torque requests more slowly.
A method is disclosed wherein reactions times of the engine and of the electric machine or machines within a hybrid powertrain are utilized to control in parallel an immediate lead torque request, controlling the engine, and an immediate torque request, controlling the electric machines, the torque requests being coordinated by respective reaction times in order to substantially effect simultaneous changes to input torque.
Because, as discussed above, changes to input torque from the engine are known to involve consistently longer reactions times than changes to input torque from an electric machine, an exemplary embodiment of the disclosed method can implement changes in torque request to the engine and the electric machine, acting in parallel as described above, including a lead period to the more quickly reacting device, the electric motor. This lead period may be developed experimentally, empirically, predictively, through modeling or other techniques adequate to accurately predict engine and electric machine operation, and a multitude of lead periods might be used by the same hybrid powertrain, depending upon different engine settings, conditions, operating and ranges and vehicle conditions. An exemplary equation that can be used in conjunction with test data or estimates of device reaction times to calculate lead period in accordance with the present disclosure includes the following equation:

TLead=TLead Reaction−TImmediate Reaction   [1]

wherein TLead equals the lead period for use in methods described herein,

    
    
        TLead Reaction represents the reaction time of the device with the longer reaction time, and
        TImmediate Reaction represents the reaction time of the device with the shorter reaction time.

Equation 1 assumes that two torque producing devices are utilized. If a different system is utilized, comprising for example, an engine with a long lead period, a first electric machine with an intermediate lead period, and a second electric machine with a short lead period, lead periods can be developed comparing all of the torque generating devices. In this exemplary system, if all three torque generating devices are involved, two lead periods, one for the engine as compared to each of the electric machines, will be utilized to synchronize the responses in each of the devices. The same system at a different time might be operating with the engine off and disengaged from the transmission, and a lead period comparing the first electric machine and the second electric machine will be utilized to synchronize the responses in the two electric machines. In this way, a lead period can be developed coordinating reaction times between various torque generating devices can be developed.

    
    


One exemplary method to utilize lead periods to implement parallel torque requests to distinct torque generating devices in order to effect substantially simultaneous changes to output torque in response to a change in operator torque request includes issuing substantially immediately a change to the engine torque immediate request, initiating within the engine a change to a new engine output torque. This new engine output torque, in conjunction with the electric motor operating state, is still managed by the HCP in order to provide some portion of the total input torque to the transmission required to propel the vehicle. From the point that the engine torque immediate request changes, the lead period expires, described above taking into account the differences in reaction times between the engine and the electric machine. After the lead period, a change to torque requests issued to the electric machine or machines, managed by the HCP in order to fulfill a portion of the operator torque request, is executed, and the electric machine changes the electric machine operating state, and as described above, the changes to the input torques provided by the engine and the electric machine change substantially simultaneously.
As described in the disclosed method above, engine torque immediate requests and torque requests to an electric machine are disclosed for use in parallel to control distinct torque generative devices with different reaction times to reaction to changes in operator torque request. Changes in operator torque request can include a simple change in desired output torque within a particular transmission operating range state, or changes in operator torque request can be required in conjunction with a transmission shift between different operating range states. Changes to operator torque requests in conjunction with a transmission shift are more complex than changes contained within a single operating range state because torques and shaft speeds of the various hybrid powertrain components must be managed in order to transition torque applied from a first clutch and to a second previously not applied clutch without the occurrence of slip, as described above.
Shifts within a transmission, as described above, frequently involve unloading a first clutch, transitioning through a freewheeling or inertia speed phase state, and subsequently loading a second clutch. Within the transmission of a conventionally powered vehicle utilizing an engine only, the change within a transmission from one fixed gear state to another fixed gear state usually includes unloading a first clutch, allowing the vehicle to briefly coast through an inertia speed phase state, and then loading a second clutch. However, as described in relation to FIG. 1 and Table 1, above, clutches within a hybrid powertrain transmission are frequently applied in pairs or groups, and a shift within the transmission can involve only unloading one of the applied clutches and subsequently loading another clutch while maintaining engagement of a third clutch throughout the shift. FIG. 4 demonstrates gear transition relationships for an exemplary hybrid powertrain transmission, in particular as described in the exemplary embodiment of FIG. 1 and Table 1, in accordance with the present disclosure. Input speed, Ni, is plotted against output speed, No. At any fixed gear state, No is determined by the corresponding Ni along the fixed gear state plots. Operation in either EVT Mode I or EVT Mode II, wherein a continuously variable gear ratio is utilized to power from a fixed input torque, for example, as provided by an electric machine, can take place in the respective zones illustrated on the graph. Clutch states, C1-C4, as described in the exemplary embodiment of FIG. 1, are described in Table 1. For instance, operation in a second fixed gear state requires clutches C1 and C2 to be applied or loaded and clutches C3 and C4 to be not applied or unloaded. While FIG. 4 describes gear transitions possible in the exemplary powertrain illustrated in FIG. 1, it will be appreciated by one having ordinary skill in the art that such a description of gear transitions is possible for any transmission of a hybrid powertrain, and the disclosure is not intended to be limited to the particular embodiment described herein.
FIG. 4 can describe operation of an exemplary system in a fixed gear state or EVT mode, as described above, and it can also be used to describe shift transitions between the various transmission operating range states. The areas and plots on the graph describe operation of the operating range states through transitions. For example, transitions between fixed gear states within an EVT mode region require operation in the EVT mode between the fixed gear states. Similarly, transition from EVT Mode I to EVT Mode II requires a transition through the second fixed gear state, located at the boundary between the two modes.
In accordance with FIGS. 1 and 4 and Table 1, an exemplary transmission shift from a third fixed gear state to a fourth fixed gear state is further described. Referring to FIG. 4, both the beginning and the preferred operating range states exist within the area of EVT Mode II. Therefore, a transition from the third gear state to the fourth gear state requires first a shift from the third fixed gear state to EVT Mode II and then a shift from EVT Mode II to the fourth fixed gear state. Referring to Table 1, a hybrid powertrain transmission, beginning in a third fixed gear state, will have clutches C2 and C4 applied. Table 1 further describes operation in EVT Mode II, the destination of the first shift, to include clutch C2 applied. Therefore, a shift from the third fixed gear state to EVT Mode II requires clutch C4 to be changed from an applied to a not applied state and requires that clutch C2 remain applied. Additionally, Table 1 describes operation in the fourth fixed gear mode, the destination of the second shift, wherein clutches C2 and C3 are applied. Therefore, a shift from EVT Mode II to the fourth fixed gear state requires clutch C3 to be applied and loaded and requires that clutch C2 remain applied. Therefore, clutches C4 and C3 are transitioned through the exemplary shift, while clutch C2 remains applied and transmitting torque to the driveline throughout the shift event.
Applied to the methods disclosed herein, changes in input torque through a transmission shift can be optimized to reduce negative effects to drivability by coordinating signal commands to various torque generative devices based upon reaction times of the various components. As described above, many transmission shifts can be broken down into three phases: a first torque phase, during which an initially applied clutch is changed from a torque-bearing, locked, and synchronized clutch state to an unlocked and desynchronized clutch state; an inertia speed phase, during which affected clutches are unlocked and in transitional states; and a second torque phase, during which a second previously not applied clutch is changed from an unlocked and desynchronized clutch state to a torque-bearing, locked, and synchronized clutch state. As aforementioned, clutch slip is preferably avoided throughout transmission shifts to avoid adverse effects on drivability, and clutch slip is created when reactive torque applied across a clutch exceeds the actual capacity torque of the clutch. Therefore, within a transmission shift event, input torques must be managed in relation to the actual capacity torque of the currently applied clutch, such that the transmission shift can be accomplished without the occurrence of slip.
While a process can be utilized to perform necessary steps in a clutch loading or unloading event in sequence, with the capacity torque of the clutch being maintained in excess of reactive torques, time involved in an unlocking transition is also important to drivability. Therefore, it is advantageous to perform associated torque requests and clutch capacity commands in parallel while still acting to prevent slip. Such parallel implementation of control changes intending to effect clutch state changes associated with a transmission shift preferably occur in as short of a time-span as possible. Therefore, coordination of capacity torque within the clutches involved in the transmission shift to the torque requests, both to the engine and to the electric machine, as described in the exemplary embodiment above, is also important to maintaining drivability through a transmission shift. FIGS. 5-7 depict exemplary processes combining to accomplish an exemplary transmission shift, in accordance with the present disclosure.
FIG. 5 is a graphical representation of torque terms associated with a clutch through an exemplary transitional unlocking state, in accordance with the present disclosure. Lines illustrated at the left extreme of the graph depict clutch operation in a locked state. The graph depicts clutch command torque by a clutch control system and a resulting estimated capacity torque. Capacity torque in a clutch resulting from a command torque is a result of many factors, including available clamping pressure, design and conditional factors of the clutch, reaction time in the clutch to changes in the clutch control system. As demonstrated in the exemplary data of the graph in the initial locked region, it is known to command a torque to a locked clutch in excess of the clutch capacity and allow the other factors affecting the clutch to determine the resulting clutch capacity. Also at the left extreme of the graph depicting clutch operation in a locked state, estimated reactive torque applied to the clutch as a result of input torque from the engine and electric machine torques is depicted. At the time labeled “Initiate Unlocking State”, logic within the clutch control system or the TCM, having determined a need to transition the clutch from locked to unlocked states, changes the command torque to some level lower than the capacity torque but still higher than the reactive torque currently applied to the clutch. At this point, mechanisms within the clutch control system, for example, variable pressure control solenoids within an exemplary hydraulic clutch control system, change settings to modulate the clamping force within the clutch. As a result, capacity torque of the clutch begins to change as the clamping force applied to the clutch changes. As discussed above, the clutch reacts to a change in command torque over a reaction time, and reaction time for a particular clutch will depend upon the particulars of the application. In the exemplary graph of FIG. 5, capacity torque reacts to a reduction in command torque and begins to reduce accordingly.
As mentioned above, during the same unlocking state, reactive torque resulting from input torque and electric machine torques must also be unloaded from the clutch. Undesirable slip results if the reactive torque is not maintained below the capacity torque throughout the unlocking state. Upon initiation of the unlocking state, at substantially the same point on FIG. 5 where the capacity torque is reduced to initiate the unlocking state, limits are initiated and imposed upon input torques from the engine and the electric machine in order to accomplish a ramping down of each to zero. As described in the method disclosed herein and in exemplary embodiments described above, changes to limits including a engine torque immediate request and an immediate torque request are executed in a coordinated process, implementing a lead period calibrated to the reaction times of the various torque providing devices, such that the resulting input torques from the devices are reduced substantially simultaneously. FIG. 5 illustrates a method to perform this coordinated change to torque requests by imposing limits upon torque requests in the form of a clutch reactive torque immediate lead min/max constraining the engine torque immediate request and a clutch reactive torque immediate min/max constraining the torque request to the electric machine. These maximum reactive torque values represent the maximum torque that is permitted to be commanded from each torque providing device: the actual engine torque immediate request and the actual immediate torque request can be less than the maximum reactive torque values, but as the maximum values reduce, so the actual torque request values will also eventually reduce. The input torques from the engine and electric machine together provide, each up to the defined maximum values, some portion of the overall input torques, with the portion of each being controlled by the HCP. As a result of the calibrated lead period, both the clutch reactive torque immediate lead min/max and the clutch reactive torque immediate min/max reduce applied reactive torque to the clutch at substantially the same time, resulting in the reduction to the actual clutch reactive torque as illustrated in FIG. 5. As will be appreciated by one having ordinary skill in the art, other safeguards will additionally need to be utilized to ensure that the capacity torque remains in excess of the reactive torque throughout the unloading process. Many such methods are contemplated, and an exemplary set of terms which might be used are depicted on FIG. 5. For instance, a calibrated offset term can be used to ensure that the command setting the clutch capacity remains in excess of the actual clutch reactive torque until the actual torque passes below some threshold. An exemplary threshold for such a purpose is defined in FIG. 5 as the calibrated threshold for reactive torque. In maintaining this capacity torque request above the actual clutch reactive torque, and remembering that all devices include a reaction time to request changes, including the clutch clamping mechanism, the delay in the change to capacity torque in response to clutch command changes in combination with this offset term will maintain the capacity torque in excess of the actual clutch reactive torque. Additionally, another threshold, a calibrated threshold for torque estimate, can be used to define the end of the torque phase. For instance, if an estimate of the clutch torque capacity, as determined by an algorithm modeling clutch operation, stays below this threshold through a calibrated period of time, then the clutch can be determined to be in an unlocked state.
FIG. 6 is a graphical representation of torque terms associated with a clutch through an exemplary transitional locking state, in accordance with the present disclosure. As described above, within many transmission shift events, a second clutch is synchronized and locked, and torque is applied to the clutch. Lines illustrated at the left extreme of the graph depict clutch operation in an unlocked state. The initiation of locking state requires a series of subordinate commands necessary to transition the clutch from an unlocked state to a locked state. As described above in relation to a transition to a second torque phase within a transmission shift, the clutch, including the shaft connected to the oncoming torque providing shafts and the shaft connected to the output member, must be synchronized. Once the clutch connective surfaces attached to these shafts have been attenuated and are moving at the same rotational velocity, clamping force can begin to be applied to the clutch to bring the clutch to a locked state and begin increasing the capacity torque of the clutch. As described above with regards to avoiding slip during a torque phase, clutch capacity must be increased before reactive torque to the clutch can be increased. In order to enable the application of input torques resulting in a reactive torque across the clutch as rapidly as possible, an increase in clutch capacity can be commanded anticipatorily to achieve an initial increase in clutch capacity coincident with the clutch reaching a locked state. Reactive torques, taking into account reaction times by utilizing a lead period by the method disclosed herein, can then be timely commanded with a short lag to follow increasing clutch capacity torque. An exemplary embodiment of this method, acting in reverse of the limits imposed to torque requests as described in FIG. 5, imposes limits upon the torque requests which can be issued to the engine and to the electric machine according to a calibrated ramp rate, selected to avoid slip. As depicted in FIG. 6, a clutch reactive torque immediate min/max acting as a constraint upon electric machine torque requests is increased after a calibrated lead period from the initiation of an increasing clutch reactive torque immediate lead min/max acting as a constraint upon engine torque requests. By utilizing the lead period, the increase in input torques from the engine and the electric machine increase reactive torque applied to the clutch substantially simultaneously, according to the methods disclosed herein. As the limits upon the torque generating devices are lifted according to the calibrated ramp rate applied to each limit, the HCP can command the engine and the electric machine to fulfill a portion of the reactive torque required from the clutch, each up to the respective maximum. In this way, torque requests to the engine and the electric machine are coordinated in order to compensate for reaction times in order to increase input torques from each substantially simultaneously through a shift event.
The calibrated ramp rate utilized in the above exemplary transmission shift is a selected value which will adjust input torque levels to the desired range quickly, but also will stay below the capacity torque for the clutch so as to avoid slip. The ramp rate may be developed experimentally, empirically, predictively, through modeling or other techniques adequate to accurately predict engine and electric machine operation, and a multitude of ramp rates might be used by the same hybrid powertrain, depending upon different engine settings, conditions, or operating ranges and behavior of the control system actuating the clutch capacity torque. The ramp rate used to decrease input torques in an unlocking event can but need not be an inverse of the ramp rate used to increase input torques in a locking event. Similarly, the lead period used to coordinate input torques can but need not be the same time span value utilized in both transmission transitional states and can be varied according to particular behaviors of a vehicle and its components.
As described above, during a transmission shift, for example, between two fixed gear states as defined in the exemplary transmission described above, the transmission passes through an inertia speed phase between a first torque phase and a second torque phase. During this inertia speed phase, the originally applied clutch and the clutch to be applied are in an unlocked state, and the input is initially spinning with a rotational velocity that was shared across the first clutch just prior to becoming unsynchronized. In order to accomplish synchronization within the second clutch to be applied and loaded in the second torque phase, inputs to be connected to the second clutch must change input speed to match the driveline attached through the transmission at some new gear ratio. A number of methods are known in the art to accomplish this synchronization. However, within a shift in a hybrid powertrain transmission, shifts usually occur through range operating state where at least one clutch is still applied while another clutch is in an inertia speed phase. This means that changes to the various torque generative devices required to create synchronization in the input speed and output speed of the second clutch still impact vehicle performance in the inertia speed phase through the still applied clutch. Therefore, the methods described herein to utilize a lead period to effect changes to input torques substantially simultaneously can additionally present advantages to drivability can continue to be utilized through an inertia speed phase.
An exemplary method to accomplish this synchronization through an inertia speed phase of a transmission shift is graphically depicted in FIG. 7, in accordance with the present disclosure. The effects of the transmission shift upon two terms descriptive of the shifting process are illustrated in two sections with a common timescale. The top section depicts the input speed, or the rotational velocity of an input shaft attached to a torque generating device, of a shaft initially connected through the first, initially applied clutch. The upper dotted line represents the velocity profile of the input speed while the first clutch is in a locked state before initiation of the shift. The bottom dotted line represents the velocity profile of the input speed that must be achieved to synchronize the input speed with the output speed of the second clutch. The transition between the two dotted lines represents the change to input speed that must take place to accomplish the shift. The bottom section of FIG. 7 depicts input acceleration, or a derivative with respect to time of the input speed. Input acceleration is described in this case as the input acceleration immediate or the acceleration profile driven with a relatively quick reaction time by an electric machine or machines, and the term closely tracks actual input acceleration. The input acceleration immediate shows the change in the rate of speed which must be accomplished in order to transition the input speed from an initial input speed at the synchronous state with the first clutch to a target input speed at the synchronous state with the second clutch. The initial flat portion describes the acceleration with which the input speed is increased before the initiation of the shift, and this constant value reflects the slope of the input speed in the left portion of the top section of the FIG. 7. At the time of the initiation of the shift, based upon operator input such as pedal position and algorithms within the transmission control system, including determining a preferred operating range state, a determination is made regarding target input speed that will be required to achieve synchronization and the target input acceleration profile required to accomplish the shift. An input acceleration rate, calculated to support a target acceleration rate after the shift is completed, can be termed an input acceleration predicted lead and describes the input acceleration that needs to exist after the inertia speed phase is completed. The input acceleration immediate lead is predicted through an algorithm factoring in operator requested torque, the preferred operating range state being transitioned to, and other relevant variables. Because, as described in the top portion of FIG. 7, the input speed must be changed through the inertia speed phase to accomplish the shift and because the input acceleration describes the rate of change of the input speed, the input acceleration of the device being controlled during the inertia speed phase must reflect the input speed change to be accomplished through the inertia speed phase. In the exemplary data displayed in FIG. 7, wherein the input speed needs to be reduced to accomplish the transmission shift, the input acceleration of the device necessarily must change to a negative value representing the change in input speed. Once the input speed has been reduced to a level enabling transition to the target input speed needed for synchronizing the input and output speeds, the input acceleration changes to match the input acceleration predicted lead. In this way, input speed and input acceleration can be controlled through an inertia speed phase to match a target input speed and target input acceleration necessary to achieve a smooth transmission shift.
As described above, a transmission shift in a hybrid powertrain transmission requires transition between operating range states, wherein an inertia speed phase must be accomplished as described above, while at least one clutch is still applied and transferring torque from the torque producing devices to the driveline. Changes to input torques, driven by torque requests to the various torque generating devices, must accomplish both the required input speed and input acceleration changes and maintain drivability throughout the inertia speed phase. Therefore, the methods described herein to utilize a lead period to effect changes to input torques substantially simultaneously can be utilized through an inertia speed phase to effect torque request changes to the various torque producing devices in order to effect substantially simultaneous changes to the input torques. FIG. 7 illustrates coordinating torque producing device reaction times, and a lead period calibrated to the difference in the related reaction times, to improve drivability in a transmission shift. An engine, as described above, includes the greater reaction time among torque generating devices. In order to adjust the input speed and input acceleration as quickly as possible to achieve the target speed and acceleration values for the shift, an input acceleration immediate lead is predicted through an algorithm. This input acceleration immediate lead includes the reaction time of the engine to changes in torque requests, and profiles the most rapid change in input speed and input acceleration in the lead device that can be accomplished to reach the target values. This rapid change in input speed must include the aforementioned reaction time in the engine to changes in torque requests and the time the engine will take to accelerate or decelerate through the input acceleration immediate lead. As depicted in FIG. 7, the input acceleration immediate lead, in anticipation of a pending shift, can initiate requisite commands to the engine in anticipation of the inertia speed phase, as the resulting input torque from the engine will not begin to reduce until later, due to the relatively long engine reaction time. Once the input acceleration immediate lead has been determined, an input acceleration immediate, following the input acceleration immediate lead by a lead period, calibrated to reaction times as described above, can be utilized to control the electric machine to match changes in input speed and input acceleration at substantially the same time as the response from the engine. In this way, the engine and the electric machines are substantially synchronized in affecting the target input speed and target acceleration.
The above methods describe cases in which a transmission is operating with a clutch or clutches engaged and with a torque being applied from at least one input torque to either an output torque or between torque generating devices. However, a neutral operating range state is known wherein all clutches are unlocked and no torque is being applied through the transmission. One having ordinary skill in the art will appreciate that for various reasons, either the engine or an electric machine can be set to an idle or operational state in a neutral condition, and that portions of the transmission attached to the running device can continue to spin. In such a neutral operating state, such portions of the transmission can apply little resistance to the spinning device and can quickly accelerate to a high rotational speed. Such portions of the transmission rotating at high speeds can cause a variety of issues, including noise and vibrations issues, damage to the spinning parts, or the spinning parts, storing kinetic energy, can cause a perceptible jerk in the transmission if subsequently connected through a clutch. The above methods, monitoring portions of the powertrain and issuing lead and immediate control signals to the torque generating devices in order to maintain control over the torques and speeds of the various portions of the powertrain, can be applied in the neutral operating range state to monitor speed of various components, monitored or predicted as a clutch slip acceleration predicted lead and by imposing limits upon clutch slip acceleration in a lead control signal as a clutch slip acceleration immediate lead and an immediate control signal as a clutch slip acceleration immediate. Operated in this way, a powertrain can be controlled through a neutral operating range state, maintaining speed of various portions of the transmission within a preferred range.
The above methods describe torque management processes as a comparison of positive values. It will be appreciated by one having ordinary skill in the art that clutch torques are described as positive and negative torques, signifying torques applied in one rotational direction or the other. The above method can be used in either positive or negative torque applications, where the magnitudes of the torques are modulated in such a way that the magnitude of the applied reactive torque does not exceed the magnitude of the torque capacity for a particular clutch. One particular corollary to minimum and maximum reactive torque values is illustrated in FIG. 8. FIG. 8 graphically illustrates an instance in which an input acceleration immediate lead has been determined for engine control through an inertia speed phase, and additionally, a corresponding input acceleration immediate has been determined for electric machine control through the inertia speed phase. In an instance where negative input acceleration or deceleration is occurring to the engine in an inertia speed phase, this condition is most commonly an instance where the engine is simply being allowed to slow down by internal frictional and pumping forces within the engine. However, when an electric machine is decelerating, this condition is most commonly accomplished with the electric machine still under power, or conversely, operating in a regeneration mode. Because the electric machine is still operating under system control and with implications with the rest of vehicle's systems, the motor is still subject to systemic restraints, for instance, battery power available to drive the motor. FIG. 8 imposes such a systemic restraint in the minimum input acceleration constraint. Where such a restraint interferes with the input acceleration immediate, algorithms within the electric machine control system modify the input acceleration immediate to accommodate the constraint. Once the constraint no longer limits electric machine operation within the input acceleration immediate, the algorithm operates to recover the input acceleration to the effect the desired changes to the input speed.
FIG. 9 shows a control system architecture for controlling and managing torque and power flow in a powertrain system having multiple torque generative devices, described hereinbelow with reference to the hybrid powertrain system shown in FIGS. 1 and 2, and residing in the aforementioned control modules in the form of executable algorithms and calibrations. The control system architecture can be applied to any powertrain system having multiple torque generative devices, including, e.g., a hybrid powertrain system having a single electric machine, a hybrid powertrain system having multiple electric machines, and non-hybrid powertrain systems.
The control system architecture of FIG. 9 depicts a flow of pertinent signals through the control modules. In operation, the operator inputs to the accelerator pedal 113 and the brake pedal 112 are monitored to determine the operator torque request (‘To_req’). Operation of the engine 14 and the transmission 10 are monitored to determine the input speed (‘Ni’) and the output speed (‘No’). A strategic optimization control scheme (‘Strategic Control’) 310 determines a preferred input speed (‘Ni_Des’) and a preferred engine state and transmission 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 engine 14, the transmission 10, and the first and second electric machines 56 and 72. The strategic optimization control scheme 310 is preferably executed by the HCP 5 during each 100 ms loop cycle and each 25 ms loop cycle.
The outputs of the strategic optimization control scheme 310 are used in a shift execution and engine start/stop control scheme (‘Shift Execution and Engine Start/Stop’) 320 to command changes in the transmission operation (‘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 C1 70, C2 62, C3 73, and C4 75 and other transmission 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 input speed and preferably comprises a scalar parametric value that is a targeted input speed for the forthcoming loop cycle. The engine operating commands and the operator torque request are based upon the input speed profile during a transition in the operating range state of the transmission.
A tactical control scheme (‘Tactical Control and Operation’) 330 is repeatedly executed during one of the control loop cycles to determine engine commands (‘Engine Commands’) for operating the engine, including a preferred input torque from the engine 14 to the transmission 10 based 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 operating state and a cylinder deactivation operating 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 clutch is estimated in the TCM 17, including the presently applied clutches and the non-applied clutches, and a present engine input torque (‘Ti’) reacting with the input member 12 is determined in the ECM 23. A motor torque control scheme (‘Output and Motor Torque Determination’) 340 is 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 machines 56 and 72 in 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 engine 14, the present operating range state, the input speed, the operator torque request, and the input speed profile. The first and second electric machines 56 and 72 are controlled through the TPIM 19 to meet the preferred motor torque commands based upon the preferred output torque. The motor torque control scheme 340 includes algorithmic code which is regularly executed during the 6.25 ms and 12.5 ms loop cycles to determine the preferred motor torque commands.
FIG. 10 is a schematic diagram exemplifying data flow through a shift execution, describing more detail exemplary execution of the control system architecture such as the system of FIG. 9 in greater detail, in accordance with the present disclosure. Powertrain control system 400 is illustrated comprising several hybrid drive components, including an engine 410, an electric machine 420, and clutch hydraulics 430. Control modules strategic control module 310, shift execution module 450, clutch capacity control module 460, tactical control and operation module 330, output torque and motor torque determination module 340, and clutch control module 490, are illustrated, processing information and issuing control commands to engine 410, electric machine 420, and clutch hydraulics 430. These control modules can be physically separate, can be grouped together in a number of different control devices, or can be entirely performed within a single physical control device. Module 310, a strategic control module, performs determinations regarding preferred powertrain operating points and preferred operating range states as described in FIG. 9. Module 450, a shift execution module, receives input from strategic control module 310 and other sources regarding shift initiation. Module 450 processes inputs regarding the reactive torque currently applied to the clutch and the preferred operating range state to be transitioned to. Module 450 then employs an algorithm, determining parameters for the execution of the shift, including hybrid range state parameters describing the balance of input torques required of the torque providing devices, details regarding a target input speed and input acceleration lead predicted required to execute the transition to the preferred operating state range, an input acceleration immediate lead as previously described, and clutch reactive torque immediate lead min/max and clutch reactive torque immediate min/max values as previously described. From module 450, clutch reactive torque parameters and hybrid range state information are fed to clutch capacity control module 460, lead control parameters and signals are fed to tactical control and operation module 330, and immediate control parameters and signals are fed to output torque and motor torque determination module 340. Clutch capacity control module 460 processes reactive torque and hybrid range state information and generates logic describing clutch reactive torque limits enabling engine control through module 330, electric machine control through module 340, and clutch control through module 490, in accordance with methods described herein. Tactical control and operation module 330 includes means to issue torque requests and execute limits upon input torque supplied from engine 410, and feed, additionally, describe the input torque supplied from the engine to module 340 for use in control of electric machine 420. Output torque and motor torque determination module 340 likewise receives and processes information to issue electric machine torque requests to electric machine 420. Additionally, module 340 generates clutch reactive torque commands for use by clutch control module 490. Module 490 processes information from modules 460 and 340 and issues hydraulic commands in order to achieve the required clutch capacity torque required to operate the transmission. This particular embodiment of data flow illustrates one possible exemplary process by which vehicular torque generative devices and related clutches can be controlled in accordance with the method disclosed herein. It will be appreciated by one having ordinary skill in the art that the particular process employed can vary, and this disclosure is not intended to limited to the particular exemplary embodiment described herein.
FIG. 11 details signal flow in the tactical control scheme (‘Tactical Control and Operation’) 330 for controlling operation of the engine 14, described with reference to the hybrid powertrain system of FIGS. 1 and 2 and the control system architecture of FIG. 9. The tactical control scheme 330 includes a tactical optimization control path 350 and a system constraints control path 360 which are preferably executed concurrently. The outputs of the tactical optimization control path 350 are input to an engine state control scheme 370. The outputs of the engine state control scheme 370 and the system constraints control path 360 are input to an engine response type determination scheme (‘Engine Response Type Determination’) 380 for controlling the engine state, the immediate engine torque request, the predicted engine torque request, and the engine response type.
The input from the engine 14 can be described in terms of an engine operating point including engine speed and engine torque which can be converted into the input speed and input torque which react with the input member from the transmission 10. When the engine 14 comprises a spark-ignition engine, a change in the engine operating point can be effected by changing mass of intake air to the engine 14 by controlling position of an engine throttle (not shown) 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 engine operating point can be effected by adjusting ignition timing, including retarding spark timing from a mean-best-torque spark timing to decrease engine torque. When the engine 14 comprises a compression-ignition engine, the engine operating point is controlled by controlling the mass of injected fuel and adjusted by retarding injection timing from a mean-best-torque injection timing to decrease the engine torque. The engine operating point can be changed to effect a change in the input torque by changing the engine state between the engine-off state and the engine-on state, by controlling the engine state between the all-cylinder state and the cylinder deactivation state, and, by controlling the engine state between the engine-fueled state and the fuel cutoff state wherein the engine is rotating and unfueled to effect engine braking.
In operation, operator inputs to the accelerator pedal 113 and to the brake pedal 112 are monitored to determine the operator torque request. Present speeds of the output member 64 and the input member 12, i.e., No and Ni, are determined. A present operating range state of the transmission 14 and present engine states are determined. Maximum and minimum electric power limits of the electric energy storage device 74 are determined.
The operator inputs to the accelerator pedal 113 and the brake pedal 112 comprise 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 selector 114 commands operation of the vehicle in the forward direction, and a similar reverse propulsion response when the vehicle operation is commanded in the reverse 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 shown in FIG. 9.
The immediate accelerator output torque request comprises an immediate torque request determined based upon the operator input to the accelerator pedal 113. The control system controls the output torque from the hybrid powertrain system in response to the immediate accelerator output torque request to cause positive acceleration of the vehicle. The immediate brake output torque request comprises an immediate braking request determined based upon the operator input to the brake pedal 112. The control system controls the output torque from the hybrid powertrain system in response to the immediate brake output torque request to cause deceleration, or negative acceleration, of the vehicle. Vehicle deceleration effected by control of the output torque from the hybrid powertrain system is combined with vehicle deceleration effected by a vehicle braking system (not shown) to decelerate the vehicle to achieve the immediate braking request.
The immediate accelerator output torque request is determined based upon a presently occurring operator input to the accelerator pedal 113, and comprises a request to generate an immediate output torque at the output member 64 preferably 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 pedal 113 and comprises an optimum or preferred output torque at the output member 64. 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 wheels 93 and the output torque generated at the output member 64 which reacts with the driveline 90 to decelerate the vehicle in response to the operator input to the brake pedal 112.
The immediate brake output torque request is determined based upon a presently occurring operator input to the brake pedal 112, and comprises a request to generate an immediate output torque at the output member 64 to effect a reactive torque with the driveline 90 which preferably decelerates the vehicle. The immediate brake output torque request is determined based upon the operator input to the brake pedal 112 and 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 member 64 in response to an operator input to the brake pedal 112 subject to a maximum brake output torque generated at the output member 64 allowable regardless of the operator input to the brake pedal 112. In one embodiment the maximum brake output torque generated at the output member 64 is 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 pedal 112. 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 selector 114 is 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 machines 56 and 72. 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 tactical optimization control path 350 acts on substantially steady-state inputs to select a preferred engine state and determine a preferred input torque from the engine 14 to the transmission 10. The inputs originate in the shift execution and engine start/stop control scheme 320. The tactical optimization control path 350 includes an optimization scheme (‘Tactical Optimization’) 354 to determine preferred input torques for operating the engine 14 in 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 (‘Engine State’). Inputs to the optimization scheme 354 include a lead operating range state of the transmission 10 (‘Lead Hybrid Range State’) a lead predicted input acceleration profile (‘Lead Input Acceleration Profile Predicted’), a predicted range of clutch reactive torques (‘Predicted Clutch Reactive Torque Min/Max’) across each applied clutch in the lead operating range state, predicted battery power limits (‘Predicted Battery Power Limits’), a predicted accelerator output torque request (‘Output Torque Request Accel Prdtd’) and a predicted braking output torque request (‘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 filter 352 to yield a net predicted output torque (‘To Net Prdtd’) and a predicted accelerator output torque (‘To Accel Prdtd’), which are inputs to the optimization scheme 354. The lead operating range state of the transmission 10 comprises a time-shifted lead of the operating range state of the transmission 10 to accommodate a response time lag between a commanded change in the operating range state and the actual operating range state. Thus the lead operating range state of the transmission 10 is the commanded operating range state. The lead predicted input acceleration profile comprises a time-shifted lead of the predicted input acceleration profile of the input member 12 to 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. Thus the lead predicted input acceleration profile is the predicted input acceleration profile of the input member 12 occurring after the time shift. The parameters designated as ‘lead’ are used to accommodate concurrent transfer of torque through the powertrain converging at the common output member 64 using devices having varying response times. Specifically, the engine 14 can have a response time of an order of magnitude of 300-600 ms, and each of the torque transfer clutches C1 70, C2 62, C3 73, and C4 75 can have response times of an order of magnitude of 150-300 ms, and the first and second electric machines 56 and 72 can have response time of an order of magnitude of 10 ms.
The optimization scheme 354 determines costs for operating the engine 14 in 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 engine 14 are input to a stabilization analysis scheme (‘Stabilization and Arbitration’) 356 along 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 (‘Optimal Engine State’).
The preferred input torques for operating the engine 14 in the all-cylinder state and in the cylinder deactivation state with and without fuel cutoff are input to an engine torque conversion calculator 355 and converted to preferred engine torques in the all-cylinder state and in the cylinder deactivation state (‘Optimal Engine Torque Full’) and (‘Optimal 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 engine 14 and the transmission 10. 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 scheme 370.
The costs for operating the engine 14 include operating costs which are 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 can be 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 operating state of the engine 14.
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 scheme 370, which includes an engine state machine (‘Engine State Machine’) 372. The engine state machine 372 determines a target engine torque (‘Target Engine Torque’) and an engine state (‘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 374 which 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 machine 372 outputs 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-fueled 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-fueled 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 scheme 3 80.
The system constraints control path 360 determines 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 transmission 10. The minimum and maximum input torques are determined based upon constraints to the transmission 10 and the first and second electric machines 56 and 72, including clutch torques and battery power limits, which affect the capacity of the transmission 10 to react input torque during the current loop cycle. Inputs to the system constraints control path 360 include the immediate output torque request as measured by the accelerator pedal 113 (‘Output Torque Request Accel Immed’) and the immediate output torque request as measured by the brake pedal 112 (‘Output Torque Request Brake Immed’) which are combined and shaped with the axle torque response type through an immediate output torque shaping filter 362 to 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 scheme 364 include the lead operating range state of the transmission 10, 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 applied clutch in the lead operating range state, and the available battery power (‘Battery Power Limits’) comprising the range PBAT—MIN to PBAT—MAX. A targeted lead input acceleration profile comprises a time-shifted lead of the immediate input acceleration profile of the input member 12 to 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 scheme 364 determines an output torque range for the transmission 10, and then determines the minimum and maximum input torques that can be reacted by the transmission 10 based upon the aforementioned inputs.
The minimum and maximum input torques are input to the engine torque conversion calculator 355 and 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 engine 14 and the transmission 10.
The filtered target engine torque, the output of the engine state machine 372 and the engine minimum and maximum engine torques are input to the engine response type determination scheme 380, which inputs the engine commands to the ECM 23 for 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.
As described above, changes in transmission operating range states involve transitioning clutches. Vehicles utilizing a plurality of clutches in various engagement states through a transition can maintain a transmission of torque through a change in operating range state. According to the exemplary four clutch transmission described above, in reference to Table 1 and FIG. 4, a number of transitions between operating range states are foreseeable. In transition from one fixed gear state to another operating range state, two clutches are initially engaged, and at least one clutch is transitioned according to a process, such as the exemplary process of FIG. 5, from a locked state to an unlocked state and at least one clutch is transitioned according to a process, such as the exemplary process of FIG. 6, from an unlocked state to a locked state. In the interim period, clutches can pass through a neutral state, but such a change is not preferable due to impacts to drivability and losses in efficiency caused by unloading and re-loading the engine in a wasteful use of fuel not contributing to the output of the powertrain. Instead, utilizing an inertia speed phase as described above in the exemplary process of FIG. 7 allows for continued transmission of torque from torque generative devices to the output throughout the change in transmission operating range states. In this way, waste and adverse impacts associated with changes through neutral can be avoided.
While changes to operating range state avoiding a neutral state are preferable, engine operation and engine torque output may not be accommodative to the change in operating range states. As described above, transitioning a clutch designed for synchronous operation from a locked state to an unlocked state requires that all torque be removed from the clutch. If two clutches are initially locked and transmitting torque from inputs including the engine, and one clutch must be unloaded prior to a pending clutch transition, an entirety of the torque being transmitted from the inputs must be transmitted by the remaining locked clutch. The remaining locked clutch has a maximum clutch torque capacity that can be transmitted through the clutch. In order to avoid slip, the total of the torques input to the transmission, in the above exemplary powertrain, TI, TA, and TB, must not exceed the capacity of the clutch transmitting the entire reactive torque to the output.
Engine output is known to change slowly, and changes in operating range state preferably include smooth output from the engine to preserve drivability and create the least perception of change to the customer through the change. Additionally, changes to engine output create inefficiencies in fuel consumption. For example, methods to quickly reduce engine output include either retarding spark timing or advancing injection timing. Both methods reduce the efficiency of the combustion process, and such reductions in efficiency accomplish changes in engine output faster than a normal throttle change. However, the reduction in efficiency results in fuel expenditure not resulting in work output as torque. Therefore, quick changes in reactive torque transmitted through the transmission are preferably accomplished through the electric machine or machines, either as torque reductions in the electric machines or in torque from the machines acting against and recovering excess torque from TI and converting it to stored energy. When such excess torque in TI exceeds the limits of torque that can be counteracted by the electric machines, changes in engine torque commands through slower throttle commands or faster changes as described above through reductions in combustion efficiency can be implemented. FIG. 12 is a graphical representation of terms describing an exemplary torque and inertia speed phase of a transmission, including minimum and maximum engine torques, in accordance with the present disclosure. As described in FIG. 7, a torque and inertia speed phase is illustrated, wherein an exemplary transmission is initially operated with two locked clutches, and upon commands initiating a transition in operating range state, a clutch is transitioned from a locked state to an unlocked state, and an input speed, NI, must transition in accordance with a destination operating range state. The second portion of the graph describes the lead operating range state in which the transmission is currently arranged. The step transition in the middle of the second portion describes the point at which the lead operating range state transitions from fixed gear to mode. This transition from locked to unlocked state in the transitioning clutch is further described in the third section of the graph, showing clutch reactive torque lead immediate minimum and maximum values converging to zero for the transitioning clutch. As described above in FIG. 5, these limits can be used to unload torque from a clutch in preparation for synchronous transition to an unlocked state. The bottom portion of the graph describes engine torque through the transition of the transmission. The predicted engine torque request describes an estimate of desired TI through the exemplary transition. Such an estimate can be developed based upon a number of factors predictive of engine output through the transmission shift, such as TO—REQ. As described in FIG. 11, engine torque hybrid minimum and maximum describes minimum and maximum engine torques imposed upon the engine through an engine control tactical scheme. As described in association with FIG. 11, a number of events requiring a reduction in To can create imposed reductions in engine torque. In the present exemplary transition in the transmission operating range state, transitions in the offloading clutch require reductions in minimum and maximum engine torques. However, the changing envelope of permissible TI values does not interact with the predicted engine torque requests. In such an exemplary transition in operating range state, TI does not need to be changed due to minimum and maximum engine torques imposed by tactical control 330. FIG. 13 is graphical representation of terms describing an exemplary torque and inertia speed phase of a transmission, including minimum and maximum engine torques acting to change engine output, in accordance with the present disclosure. FIG. 13 describes, similarly to FIG. 12, changes to NI, operating range state, and clutch reactive torque lead immediate minimum and maximum values associated with a change in transmission operating range state. However, in the exemplary transition of FIG. 13, minimum and maximum engine torques, imposed by an engine tactical control scheme in light of electric machine capacities and other variables describing the required changes in torque, interact with and impose selective changes upon engine output in the form of an immediate engine torque request. As described above, such changes in engine torque can be accomplished in a number of ways including changes to combustion efficiency. In such circumstances, engine torque can be managed to accommodate limits required upon TI in order to achieve reactive torque within the transmission within acceptable limits as required for the transition to operating range state.
It is understood that modifications are allowable within the scope of the disclosure. The disclosure has been described with specific reference to the preferred 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 disclosure.

## Claims

1. Method for controlling a powertrain comprising an electro-mechanical transmission mechanically-operatively coupled to an internal combustion engine and an electric machine adapted to selectively transmit mechanical power to an output member through selective application of a plurality of clutches, said method comprising:
commanding a shift from a fixed gear operating range state to a second operating range state, said second operating range state achieved without activating an oncoming clutch;
commanding decreased reactive torque through an off-going clutch during a torque phase of said commanded shift; and
operating a control module to decrease said reactive torque through said off-going clutch through control of engine input torque, comprising monitoring a requested output torque,
monitoring factors describing input torque constraints required to offload said off-going clutch without causing clutch slip,
estimating a predicted engine torque request based upon said requested output torque through said commanded shift,
determining minimum and maximum engine torques based upon said monitoring factors, and
when said predicted engine torque request exceeds said maximum engine torque, imposing an immediate engine torque request upon said engine to offload said off-going clutch without causing clutch slip.

2. The method of claim 1, wherein said decreasing said reactive torque across said off-going clutch through control of engine input torque further comprises:
when said decreasing cannot be accomplished solely by said electric machine, imposing an immediate engine torque request upon said engine.

3. The method of claim 2, wherein said imposing an immediate engine Torque request upon said engine comprises retarding a spark timing.

4. The method of claim 2, wherein said imposing an immediate engine torque request upon said engine comprises advancing an injection timing.

5. The method of claim 2, wherein said imposing an immediate engine torque request upon said engine comprises commanding an engine throttle change.

6. The method of claim 1, wherein said transmission is further coupled to a second electric machine; and wherein said decreasing said reactive torque across said off-going clutch through control of engine input torque comprises:
when said decreasing cannot be accomplished by said electric machine and said second electric machine, imposing an immediate engine torque request upon said engine.

7. The method of claim 6, wherein said imposing an immediate engine Torque request upon said engine comprises retarding a spark timing.

8. Said method of claim 6, wherein said imposing a immediate engine Torque request upon said engine comprises advancing an injection timing.

9. The method of claim 6, wherein said imposing a immediate engine Torque request upon said engine comprises commanding an engine throttle change.

10. The method of claim 1, wherein said monitoring factors describing input torque constraints required to offload said off-going clutch without causing slip comprises:
monitoring a clutch reactive torque lead immediate minimum and a clutch reactive torque lead immediate maximum.

11. The method of claim 10, wherein said monitoring factors describing Input torque constraints required to offload said off-going clutch without causing slip further comprises:
monitoring a clutch torque capacity for a load bearing clutch.

12. The method of claim 10, wherein said monitoring factors describing Input torque constraints required to offload said off-going clutch without causing slip further comprises:
monitoring an input speed curve to be achieved through said commanded shift.

13. Method for controlling a powertrain comprising an electro-mechanical transmission mechanically-operatively coupled to an internal combustion engine and first and second electric machine adapted to selectively transmit power to an output member through selective application of a plurality of clutches, said method comprising:
monitoring a commanded shift from a fixed gear operating range state to a second operating range state, said second operating range state achieved without activating an oncoming clutch;
operating a control module to command a decreased reactive torque through an off-going clutch during a torque phase of said commanded shift;
determining a maximum engine torque based upon said commanded shift and said commanded decreased reactive torque;
estimating a predicted engine torque request through said commanded shift; and
when said predicted engine torque request exceeds said maximum engine torque, controlling an engine input torque based upon said maximum engine torque;
wherein commanding the decreased reactive torque through said off-going clutch during a torque phase of said commanded shift comprises:
monitoring a requested output torque;
monitoring factors describing input torque constraints required to offload said off-going clutch without causing clutch slip;
estimating a predicted engine torque request based upon said requested output torque through said commanded shift;
determining minimum and maximum engine torques based upon said monitoring factors; and
when said predicted engine torque request exceeds said maximum engine torque, imposing an immediate engine torque request upon said engine to decrease the reactive torque of the off-going clutch without causing clutch slip.

14. The method of claim 13, wherein said controlling said engine input Torque comprises retarding a spark timing.

15. The method of claim 13, wherein said controlling said engine input Torque comprises advancing an injection timing.

16. The method of claim 13, wherein said controlling said engine input Torque comprises commanding an engine throttle change.