Abstract:
A multivariable feedback control approach to actively dampen magnitude of jerks in a powertrain system using multiple torque-control devices is offered. To manage jerks, a desired axle torque is restricted when a torque reversal occurs. When the vehicle operator or the system executes a command that requires change in direction of torque, the desired axle torque is limited to a low level until the lash estimate has changed accordingly. During this transition time, active damping controls driveline component speeds so that the effect of lash take-up is minimized. After lash take-up occurs, the desired axle torque proceeds without restriction. The invention includes determining a desired axle torque, an output speed of the transmission, and an output speed of a driven wheel of the driveline. One of the devices is controlled based upon a time-rate change in the desired axle torque.

Description:
TECHNICAL FIELD  
       [0001]     This invention pertains generally to hybrid powertrain control systems, and more specifically to controlling driveline jerk management by controlling multiple torque inputs.  
       BACKGROUND OF THE INVENTION  
       [0002]     Various hybrid powertrain architectures are known for managing the input and output torques of various prime-movers in hybrid vehicles, most commonly internal combustion engines and electric machines. Series hybrid architectures are generally characterized by an internal combustion engine driving an electric generator which in turn provides electrical power to an electric drivetrain and to a battery pack. The internal combustion engine in a series hybrid is not directly mechanically coupled to the drivetrain. The electric generator may also operate in a motoring mode to provide a starting function to the internal combustion engine, and the electric drivetrain may recapture vehicle braking energy by operating in a generator mode to recharge the battery pack. Parallel hybrid architectures are generally characterized by an internal combustion engine and an electric motor which both have a direct mechanical coupling to the drivetrain. The drivetrain conventionally includes a shifting transmission to provide the preferable gear ratios for wide range operation.  
         [0003]     One hybrid powertrain architecture comprises a two-mode, compound-split, electromechanical transmission which utilizes an input member for receiving power from a prime mover power source and an output member for delivering power from the transmission. First and second motor/generators are operatively connected to an energy storage device for interchanging electrical power between the storage device and the first and second motor/generators. A control unit is provided for regulating the electrical power interchange between the energy storage device and the first and second motor/generators. The control unit also regulates electrical power interchange between the first and second motor/generators.  
         [0004]     Engineers have a challenge in managing transitions in operating states of hybrid powertrain systems to minimize effect on vehicle driveability caused by driveline lash, or play, in the entire gear train. Actions wherein driveline torque is transitioned from a neutral torque to a positive or negative torque, or from a positive torque to a negative torque, can result in gear lash, and jerks, as slack is taken out of the driveline and driveline components impact one another. Excessive gear lash, jerks, and other related events may result in operator dissatisfaction, and can negatively affect powertrain and transmission reliability and durability.  
         [0005]     Gear lash and jerks have the potential to occur during vehicle operations including: when the operator changes transmission gears, e.g. from neutral/park to drive or reverse, or when the operator tips into the throttle. Lash action occurs, for example, as follows: Torque-generative devices of the powertrain exert a positive torque onto the transmission input gears to drive the vehicle through the driveline. During a subsequent deceleration, torque input to the powertrain and driveline decreases, and gears in the transmission and driveline separate. After passing through a zero-torque point, the gears reconnect to transfer torque, in the form of motor braking, electrical generation, and others. The reconnection of the gears to transfer torque result in gear impact, with resulting jerks.  
         [0006]     Hybrid powertrain systems such as the exemplary two-mode, compound-split, electro-mechanical transmission have multiple torque-generative devices. Coordinated control of the torque-generative devices is required to reduce driveline gear lash and jerks. Additionally, the exemplary hybrid powertrain system introduces a challenge of managing driveline transitions which may occur when one of the motor/generators transitions from operating in a motoring mode to operating in a generating mode.  
         [0007]     Therefore, there is a need for a control scheme for hybrid powertrain systems such as the exemplary two-mode, compound-split, electromechanical transmission having multiple torque-generative devices which addresses the aforementioned issues related to driveline gear lash and jerks. This includes a scheme that is cognizant of driveline torque transitions which may occur when one of the motor/generators transitions from operating in a motoring mode to operating in a generating mode. There is a further need to develop a hybrid powertrain control system which can coordinate and manage power from the torque-generative devices in a manner which effectively uses on-board computing resources.  
       SUMMARY OF THE INVENTION  
       [0008]     The invention provides a multivariable feedback control approach to actively dampen magnitude of jerks in a hybrid powertrain system, and other powertrain systems using multiple torque control devices.  
         [0009]     To manage jerks, desired axle torque T A     —     DES  is restricted when a torque reversal occurs. If the vehicle operator or the system executes a command that requires the system to change from a positive torque to a negative torque, or a negative torque to a positive torque, the desired axle torque during the reversal is limited to a low level until the lash estimate has changed accordingly, i.e. from positive to negative, or negative to positive. During this transition time, active damping controls the response of the driveline component speeds so that the effect of lash take-up is minimized. After lash take-up occurs, the desired axle torque can proceed without restriction to the operator or system command.  
         [0010]     Therefore, an aspect of the present invention includes a method and apparatus to control motive torque to a driveline of a hybrid powertrain system. The hybrid powertrain system comprises a plurality of torque-generative devices operably connected to a transmission operable to transmit motive torque to an axle of the driveline. The torque-generative devices preferably comprise electric machines, or motor/generators. The method includes determining a desired axle torque, an output speed of the transmission, and an output speed of a driven wheel of the driveline. One of the torque-generative devices is controlled based upon a time-rate change in the desired axle torque. Controlling each of the torque-generative devices preferably occurs when the output speed of the driven wheel is less than a predetermined value, such as during a vehicle launch from at or near zero vehicle speed.  
         [0011]     An aspect of the invention includes determining the desired axle torque by monitoring operator input to an accelerator pedal, and to a brake pedal.  
         [0012]     Another aspect of the invention includes controlling a transition between a torque-generative mode and an electric-generative mode to prevent driveline jerk when the torque-generative device comprises an electrical machine.  
         [0013]     An aspect of the invention comprises controlling driveline torque during vehicle launch, or, during a change in a fixed gear ratio of a transmission of the powertrain.  
         [0014]     These and other aspects of the invention will become apparent to those skilled in the art upon reading and understanding the following detailed description of the embodiments.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0015]     The invention may take physical form in certain parts and arrangement of parts, the preferred embodiment of which will be described in detail and illustrated in the accompanying drawings which form a part hereof, and wherein:  
         [0016]      FIG. 1  is a schematic diagram of an exemplary powertrain, in accordance with the present invention;  
         [0017]      FIG. 2  is a schematic diagram of an exemplary control architecture and powertrain, in accordance with the present invention;  
         [0018]      FIGS. 3, 4 , and  5  are schematic information flow diagrams, in accordance with the present invention; and,  
         [0019]      FIG. 6  is a representative data graph, in accordance with the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0020]     Referring now to the drawings, wherein the showings are for the purpose of illustrating the invention only and not for the purpose of limiting the same,  FIGS. 1 and 2  show a system comprising an engine  14 , transmission  10 , control system, and driveline which has been constructed in accordance with an embodiment of the present invention.  
         [0021]     Mechanical aspects of exemplary transmission  10  are disclosed in detail in commonly assigned U.S. Patent Application Publication No. U.S. 2005/0137042 A1, published Jun. 23, 2005, entitled  Two - Mode, Compound - Split Hybrid Electro - Mechanical Transmission having Four Fixed Ratios , which is incorporated herein by reference. The exemplary two-mode, compound-split, electromechanical hybrid transmission embodying the concepts of the present invention is depicted in  FIG. 1 , and is designated generally by the numeral  10 . The hybrid transmission  10  has an input member  12  that may be in the nature of a shaft which may be directly driven by an engine  14 . A transient torque damper  20  is incorporated between the output shaft  18  of the engine  14  and the input member  12  of the hybrid transmission  10 . The transient torque damper  20  preferably comprises a torque transfer device  77  having characteristics of a damping mechanism and a spring, shown respectively as  78  and  79 . The transient torque damper  20  permits selective engagement of the engine  14  with the hybrid transmission  10 , but it must be understood that the torque transfer device  77  is not utilized to change, or control, the mode in which the hybrid transmission  10  operates. The torque transfer device  77  preferably comprises a hydraulically operated friction clutch, referred to as clutch C 5 .  
         [0022]     The engine  14  may be any of numerous forms of internal combustion engines, such as a spark-ignition engine or a compression-ignition engine, readily adaptable to provide a power output to the transmission  10  at a range of operating speeds, from idle, at or near 600 revolutions per minute (RPM), to over 6,000 RPM. Irrespective of the means by which the engine  14  is connected to the input member  12  of the transmission  10 , the input member  12  is connected to a planetary gear set  24  in the transmission  10 .  
         [0023]     Referring specifically now to  FIG. 1 , the hybrid transmission  10  utilizes three planetary-gear sets  24 ,  26  and  28 . The first planetary gear set  24  has an outer gear member  30  that may generally be designated as a ring gear, which circumscribes an inner gear member  32 , generally designated as a sun gear. A plurality of planetary gear members  34  are rotatably mounted on a carrier  36  such that each planetary gear member  34  meshingly engages both the outer gear member  30  and the inner gear member  32 .  
         [0024]     The second planetary gear set  26  also has an outer gear member  38 , generally designated as a ring gear, which circumscribes an inner gear member  40 , generally designated as a sun gear. A plurality of planetary gear members  42  are rotatably mounted on a carrier  44  such that each planetary gear  42  meshingly engages both the outer gear member  38  and the inner gear member  40 .  
         [0025]     The third planetary gear set  28  also has an outer gear member  46 , generally designated as a ring gear, which circumscribes an inner gear member  48 , generally designated as a sun gear. A plurality of planetary gear members  50  are rotatably mounted on a carrier  52  such that each planetary gear  50  meshingly engages both the outer gear member  46  and the inner gear member  48 .  
         [0026]     Ratios of teeth on ring gears/sun gears are typically based upon design considerations known to skilled practitioners and outside the scope of the present invention. By way of example, in one embodiment, the ring gear/sun gear tooth ratio of the planetary gear set  24  is 65/33; the ring gear/sun gear tooth ratio of the planetary gear set  26  is 65/33; and the ring gear/sun gear tooth ratio of the planetary gear set  28  is 94/34.  
         [0027]     The three planetary gear sets  24 ,  26  and  28  each comprise simple planetary gear sets. Furthermore, the first and second planetary gear sets  24  and  26  are compounded in that the inner gear member  32  of the first planetary gear set  24  is conjoined, as through a hub plate gear  54 , to the outer gear member  38  of the second planetary gear set  26 . The conjoined inner gear member  32  of the first planetary gear set  24  and the outer gear member  38  of the second planetary gear set  26  are continuously connected to a first motor/generator  56 , also referred to as ‘Motor A’.  
         [0028]     The planetary gear sets  24  and  26  are further compounded in that the carrier  36  of the first planetary gear set  24  is conjoined, as through a shaft  60 , to the carrier  44  of the second planetary gear set  26 . As such, carriers  36  and  44  of the first and second planetary gear sets  24  and  26 , respectively, are conjoined. The shaft  60  is also selectively connected to the carrier  52  of the third planetary gear set  28 , as through a torque transfer device  62  which, as will be hereinafter more fully explained, is employed to assist in the selection of the operational modes of the hybrid transmission  10 . The carrier  52  of the third planetary gear set  28  is connected directly to the transmission output member  64 .  
         [0029]     In the embodiment described herein, wherein the hybrid transmission  10  is used in a land vehicle, the output member  64  is operably connected to a driveline comprising a gear box  90  or other torque transfer device which provides a torque output to one or more vehicular axles  92  or half-shafts (not shown). The axles  92 , in turn, terminate in drive members  96 . The drive members  96  may be either front or rear wheels of the vehicle on which they are employed, or they may be a drive gear of a track vehicle. The drive members  96  may have some form of wheel brake  94  associated therewith. The drive members each have a speed parameter, N WHL , comprising rotational speed of each wheel  96  which is typically measurable with a wheel speed sensor.  
         [0030]     The inner gear member  40  of the second planetary gear set  26  is connected to the inner gear member  48  of the third planetary gear set  28 , as through a sleeve shaft  66  that circumscribes shaft  60 . The outer gear member  46  of the third planetary gear set  28  is selectively connected to ground, represented by the transmission housing  68 , through a torque transfer device  70 . Torque transfer device  70 , as is also hereinafter explained, is also employed to assist in the selection of the operational modes of the hybrid transmission  10 . The sleeve shaft  66  is also continuously connected to a second motor/generator  72 , also referred to as ‘Motor B’.  
         [0031]     All the planetary gear sets  24 ,  26  and  28  as well as the two motor/generators  56  and  72  are coaxially oriented, as about the axially disposed shaft  60 . Motor/generators  56  and  72  are both of an annular configuration which permits them to circumscribe the three planetary gear sets  24 ,  26  and  28  such that the planetary gear sets  24 ,  26  and  28  are disposed radially inwardly of the motor/generators  56  and  72 . This configuration assures that the overall envelope, i.e., the circumferential dimension, of the transmission  10  is minimized.  
         [0032]     A torque transfer device  73  selectively connects the sun gear  40  with ground, i.e., with transmission housing  68 . A torque transfer device  75  is operative as a lock-up clutch, locking planetary gear sets  24 ,  26 , motors  56 ,  72  and the input to rotate as a group, by selectively connecting the sun gear  40  with the carrier  44 . The torque transfer devices  62 ,  70 ,  73 ,  75  are all friction clutches, respectively referred to as follows: clutch C 1   70 , clutch C 2   62 , clutch C 3   73 , and clutch C 4   75 . Each clutch is preferably hydraulically actuated, receiving pressurized hydraulic fluid from a pump. Hydraulic actuation is accomplished using a known hydraulic fluid circuit, which is not described in detail herein.  
         [0033]     The hybrid transmission  10  receives input motive torque from a plurality of torque-generative devices, including the engine  14  and the motors/generators  56  and  72 , as a result of energy conversion from fuel or electrical potential stored in an electrical energy storage device (ESD)  74 . The ESD  74  typically comprises one or more batteries. Other electrical energy and electrochemical energy storage devices that have the ability to store electric power and dispense electric power may be used in place of the batteries without altering the concepts of the present invention. The ESD  74  is preferably sized based upon factors including regenerative requirements, application issues related to typical road grade and temperature, and propulsion requirements such as emissions, power assist and electric range. The ESD  74  is high voltage DC-coupled to transmission power inverter module (TPIM)  19  via DC lines or transfer conductors  27 . The TPIM  19  is an element of the control system described hereinafter with regard to  FIG. 2 . The TPIM  19  communicates with the first motor/generator  56  by transfer conductors  29 , and the TPIM  19  similarly communicates with the second motor/generator  72  by transfer conductors  31 . Electrical current is transferable to or from the ESD  74  in accordance with whether the ESD  74  is being charged or discharged. TPIM  19  includes the pair of power inverters and respective motor controllers configured to receive motor control commands and control inverter states therefrom for providing motor drive or regeneration functionality.  
         [0034]     In motoring control, the respective inverter receives current from the DC lines and provides AC current to the respective motor over transfer conductors  29  and  31 . In regeneration control, the respective inverter receives AC current from the motor over transfer conductors  29  and  31  and provides current to the DC lines  27 . The net DC current provided to or from the inverters determines the charge or discharge operating mode of the electrical energy storage device  74 . Preferably, Motor A  56  and Motor B  72  are three-phase AC machines and the inverters comprise complementary three-phase power electronics.  
         [0035]     Referring again to  FIG. 1 , a drive gear  80  may be presented from the input member  12 . As depicted, the drive gear  80  fixedly connects the input member  12  to the outer gear member  30  of the first planetary gear set  24 , and the drive gear  80 , therefore, receives power from the engine  14  and/or the motor/generators  56  and/or  72  through planetary gear sets  24  and/or  26 . The drive gear  80  meshingly engages an idler gear  82  which, in turn, meshingly engages a transfer gear  84  that is secured to one end of a shaft  86 . The other end of the shaft  86  may be secured to a hydraulic/transmission fluid pump and/or power take-off (‘PTO’) unit, designated either individually or collectively at  88 , and comprise an accessory load.  
         [0036]     Referring now to  FIG. 2 , a schematic block diagram of the control system, comprising a distributed controller architecture, is shown. The elements described hereinafter comprise a subset of an overall vehicle control architecture, and are operable to provide coordinated system control of the powertrain system described herein. The control system is operable to synthesize pertinent information and inputs, and execute algorithms to control various actuators to achieve control targets, including such parameters as fuel economy, emissions, performance, driveability, and protection of hardware, including batteries of ESD  74  and motors  56 ,  72 . The distributed controller architecture includes engine control module (‘ECM’)  23 , transmission control module (‘TCM’)  17 , battery pack control module (‘BPCM’)  21 , and Transmission Power Inverter Module (‘TPIM’)  19 . A hybrid control module (‘HCP’)  5  provides overarching control and coordination of the aforementioned controllers. There is a User Interface (‘UI’)  13  operably connected to a plurality of devices through which a vehicle operator typically controls or directs operation of the powertrain, including the transmission  10 . Exemplary vehicle operator inputs to the UI  13  include an accelerator pedal, a brake pedal, transmission gear selector, and, vehicle speed cruise control. Each of the aforementioned controllers communicates with other controllers, sensors, and actuators via a local area network (‘LAN’) bus  6 . The LAN bus  6  allows for structured communication of control parameters and commands between the various controllers. The specific communication protocol utilized is application-specific. By way of example, one communications protocol is the Society of Automotive Engineers standard J1939. The LAN bus and appropriate protocols provide for robust messaging and multi-controller interfacing between the aforementioned controllers, and other controllers providing functionality such as antilock brakes, traction control, and vehicle stability.  
         [0037]     The HCP  5  provides overarching control of the hybrid powertrain system, serving to coordinate operation of the ECM  23 , TCM  17 , TPIM  19 , and BPCM  21 . Based upon various input signals from the UI  13  and the powertrain, the HCP  5  generates various commands, including: an engine torque command, T F     —     CMD ; clutch torque commands, T CL     —     N  for the various clutches C 1 , C 2 , C 3 , C 4  of the hybrid transmission  10 ; and motor torque commands, T A     —     CMD  and T B     —     CMD , for the electrical motors A and B, respectively.  
         [0038]     The ECM  23  is operably connected to the engine  14 , and functions to acquire data from a variety of sensors and control a variety of actuators, respectively, of the engine  14  over a plurality of discrete lines collectively shown as aggregate line  35 . The ECM  23  receives the engine torque command, T E     —     CMD , from the HCP  5 , and generates a desired axle torque, T AXLE     —     DES , and an indication of actual engine torque, T E     —     ACT , which is communicated to the HCP  5 . For simplicity, ECM  23  is shown generally having bidirectional interface with engine  14  via aggregate line  35 . Various other parameters that may be sensed by ECM  23  include engine coolant temperature, engine input speed (N E ) to a shaft leading to the transmission, manifold pressure, ambient air temperature, and ambient pressure. Various actuators that may be controlled by the ECM  23  include fuel injectors, ignition modules, and throttle control modules.  
         [0039]     The TCM  17  is operably connected to the transmission  10  and functions to acquire data from a variety of sensors and provide command signals to the transmission. Inputs from the TCM  17  to the HCP  5  include estimated clutch torques, T CL     —     N     —     EST , for each of the clutches C 1 , C 2 , C 3 , and, C 4  and rotational speed, N o , of the output shaft  64 . Other actuators and sensors may be used to provide additional information from the TCM to the HCP for control purposes.  
         [0040]     The BPCM  21  is signally connected one or more sensors operable to monitor electrical current or voltage parameters of the ESD  74  to provide information about the state of the batteries to the HCP  5 . Such information includes battery state-of-charge, Bat_SOC, and other states of the batteries, including voltage, V BAT , and available power, P BAT     —     Min , and P BAT     —     Max .  
         [0041]     The Transmission Power Inverter Module (TPIM)  19  includes a pair of power inverters and motor controllers configured to receive motor control commands and control inverter states therefrom to provide motor drive or regeneration functionality. The TPIM  19  is operable to generate torque commands for Motors A and B, T A     —     CMD  and T B     —     CMD , based upon input from the HCP  5 , which is driven by operator input through UI  13  and system operating parameters. The predetermined torque commands for Motors A and B, T A     —     CMD  and T B     —     CMD , are adjusted with motor damping torques, T A     —     DAMP  and T B     —     DAMP , to determine motor torques, T A  and T B , which are implemented by the control system, including the TPIM  19 , to control the motors A and B. Individual motor speed signals, N A  and N B  for Motor A and Motor B respectively, are derived by the TPIM  19  from the motor phase information or conventional rotation sensors. The TPIM  19  determines and communicates motor speeds, N A  and N B , to the HCP  5 . The electrical energy storage device  74  is high-voltage DC-coupled to the TPIM  19  via DC lines  27 . Electrical current is transferable to or from the TPIM  19  in accordance with whether the ESD  74  is being charged or discharged.  
         [0042]     Each of the aforementioned controllers is preferably a general-purpose digital computer generally comprising a microprocessor or central processing unit, read only memory (ROM), random access memory (RAM), electrically programmable read only memory (EPROM), high speed clock, analog to digital (A/D) and digital to analog (D/A) circuitry, and input/output circuitry and devices (I/O) and appropriate signal conditioning and buffer circuitry. Each controller has a set of control algorithms, comprising resident program instructions and calibrations stored in ROM and executed to provide the respective functions of each computer. Information transfer between the various computers is preferably accomplished using the aforementioned LAN  6 .  
         [0043]     Algorithms for control and state estimation in each of the controllers are typically executed during preset loop cycles such that each algorithm is executed at least once each loop cycle. Algorithms stored in the non-volatile memory devices are executed by one of the central processing units and are operable to monitor inputs from the sensing devices and execute control and diagnostic routines to control operation of the respective device, using preset calibrations. Loop cycles are typically executed at regular intervals, for example each 3, 6.25, 15, 25 and 100 milliseconds during ongoing engine and vehicle operation. Alternatively, algorithms may be executed in response to occurrence of an event.  
         [0044]     In response to an operator&#39;s action, as captured by the UI  13 , the supervisory HCP controller  5  and one or more of the other controllers determine required transmission output torque, T o . Selectively operated components of the hybrid transmission  10  are appropriately controlled and manipulated to respond to the operator demand. For example, in the exemplary embodiment shown in  FIGS. 1 and 2 , when the operator has selected a forward drive range and manipulates either the accelerator pedal or the brake pedal, the HCP  5  determines an output torque for the transmission, which affects how and when the vehicle accelerates or decelerates. Final vehicle acceleration is affected by other factors, including, e.g., road load, road grade, and vehicle mass. The HCP  5  monitors the parametric states of the torque-generative devices, and determines the output of the transmission required to arrive at the desired torque output. Under the direction of the HCP  5 , the transmission  10  operates over a range of output speeds from slow to fast in order to meet the operator demand.  
         [0045]     The two-mode, compound-split, electromechanical hybrid transmission, includes output member  64  which receives output power through two distinct gear trains within the transmission  10 , and operates in several transmission operating modes, described with reference now to  FIG. 1 , and Table 1, below.  
                                                 TABLE 1                                   Transmission Operating Mode   Actuated Clutches                                        Mode I   C1 70               Fixed Ratio 1   C1 70   C4 75           Fixed Ratio 2   C1 70   C2 62           Mode II   C2 62           Fixed Ratio 3   C2 62   C4 75           Fixed Ratio 4   C2 62   C3 73                      
 
         [0046]     The various transmission operating modes described in the table indicate which of the specific clutches C 1 , C 2 , C 3 , C 4  are engaged or actuated for each of the operating modes. Additionally, in various transmission operating modes, Motor A  56  or Motor B  72  may each operate as electrical motors, designated as MA, MB respectively, and whether motor A  56  is operating as a generator, designated as GA. A first mode, or gear train, is selected when the torque transfer device  70  is actuated in order to “ground” the outer gear member  46  of the third planetary gear set  28 . A second mode, or gear train, is selected when the torque transfer device  70  is released and the torque transfer device  62  is simultaneously actuated to connect the shaft  60  to the carrier  52  of the third planetary gear set  28 . Other factors outside the scope of the invention affect when the electrical machines  56 ,  72  operate as motors and generators, and are not discussed herein.  
         [0047]     The control system, shown primarily in  FIG. 2 , is operable to provide a range of transmission output speeds, N o , of shaft  64  from relatively slow to relatively fast within each mode of operation. The combination of two modes with a slow-to-fast output speed range in each mode allows the transmission  10  to propel a vehicle from a stationary condition to highway speeds, and meet various other requirements as previously described. Additionally, the control system coordinates operation of the transmission  10  so as to allow synchronized shifts between the modes.  
         [0048]     The first and second modes of operation refer to circumstances in which the transmission functions are controlled by one clutch, i.e. either clutch C 1   62  or C 2   70 , and by the controlled speed and torque of the motor/generators  56  and  72 . Certain ranges of operation are described below in which fixed ratios are achieved by applying an additional clutch. This additional clutch may be clutch C 3   73  or C 4   75 , as shown in the table, above.  
         [0049]     When the additional clutch is applied, fixed ratio of input-to-output speed of the transmission, i.e. N I /N o , is achieved. The rotations of the motor/generators  56 ,  72  are dependent on internal rotation of the mechanism as defined by the clutching and proportional to the input speed, N I , determined or measured at shaft  12 . The motor/generators function as motors or generators. They are completely independent of engine to output power flow, thereby enabling both to be motors, both to function as generators, or any combination thereof. This allows, for instance, during operation in Fixed Ratio  1  that motive power output from the transmission at shaft  64  is provided by power from the engine and power from Motors A and B, through planetary gear set  28  by accepting power from the energy storage device  74 .  
         [0050]     The transmission operating mode can be switched between Fixed Ratio operation and Mode operation by activating or deactivating one the additional clutches during Mode I or Mode II operation. Determination of operation in fixed ratio or mode control is by algorithms executed by the control system, and is outside the scope of this invention.  
         [0051]     The modes of operation may overlap the ratio of operation, and selection depends again on the driver&#39;s input and response of the vehicle to that input. RANGE  1  falls primarily within mode I operation when clutches C 1   70  and C 4   75  are engaged. RANGE  2  falls within mode I and mode II when clutches C 2   62  and C 1   70  are engaged. A third fixed ratio range is available primarily during mode II when clutches C 2   62  and C 4   75  are engaged, and a fourth fixed ratio range is available during mode II when clutches C 2   62  and C 3   73  are engaged. It is notable that ranges of operation for Mode I and Mode II typically overlap significantly.  
         [0052]     Output of the exemplary powertrain system described hereinabove is constrained due to mechanical and system limitations. The output speed, N o , of the transmission measured at shaft  64  is limited due to limitations of engine output speed, N E , measured at shaft  18 , and transmission input speed, N o , measured at shaft  12 , and speed limitations of the electric motors A and B, designated as ±N A , ±N B . Output torque, T o , of the transmission  64  is similarly limited due to limitations of the engine input torque, T E , and input torque, T 1 , measured at shaft  12  after the transient torque damper  20 , and torque limitations (T A     —     MAX , T A     —     MIN , T B     —     MAX , T B     —     MIN ) of the motors A and B  56 ,  72 .  
         [0053]     Referring now to  FIG. 3 , a control scheme is shown, comprising a multivariate feedback control system preferably executed as algorithms in the controllers of the control system described hereinabove with reference to  FIG. 2 , to control operation of the system described with reference to  FIG. 1 . The control scheme described hereinafter comprises a subset of overall vehicle control architecture. The control scheme comprises a method and apparatus for multivariate active driveline damping. An exemplary method and apparatus for multivariate active driveline damping is described in commonly assigned and co-pending U.S. Ser. No. 10/xxx,xxx: entitled M ETHOD AND  A PPARATUS FOR  M ULTIVARIATE  A CTIVE  D RIVELINE  D AMPING , attorney docket number GP-307477. The aforementioned method and apparatus are incorporated herein by reference so that multivariate active driveline damping need not be described in detail. The exemplary multivariate feedback control method and system comprises basic elements for controlling torque outputs from the torque-generative devices  14 ,  56 ,  72  through the transmission  10  to the driveline. This includes the overall control elements of determining desired operating state parameters for the powertrain system and the driveline, which comprise inputs to the desired dynamics segment  210 . Outputs of the desired dynamics segment  210  comprise a plurality of reference values for axle torque, T AXLE     —     REF ; for damper torque, T DAMP     —     REF ; and various speeds, N A     —     REF , N B     —     REF , N O     —     REF , N E     —     REF , N WHL     —     REF . The reference values and the plurality of operating state errors calculated from outputs of the driveline comprise inputs to a motor damping torque control scheme  220 . The motor damping torque control scheme  220  is executed to determine damping torques to the torque-generative devices, in this embodiment to Motors A and B, i.e. T A     —     DAMP  and T B     —     DAMP  Driveline dynamic control, shown as  230 , comprises controlling inputs to each torque-generative device and other torque devices in the transmission and driveline, based upon the operating state errors and, the reference states.  
         [0054]     Referring now to  FIG. 4 , the method and apparatus for estimating state parameters for multivariate driveline having a driveline dynamics estimator  240 , is shown. An exemplary method and apparatus for multivariate active driveline damping is described in commonly assigned and co-pending U.S. Ser. No. 10/xxx,xxx: entitled P ARAMETER  S TATE  E ESTIMATION , attorney docket number GP-307478. In overall operation, the driveline dynamics estimator  240  is a mathematical model comprising a plurality of linear equations executed as algorithms within one of the controllers. The mathematical model equations, including calibration values, are executed using algorithms to model representations of operation of the exemplary driveline described with reference to  FIGS. 1 and 2 , taking into account application-specific masses, inertias, friction factors, and other characteristics and parameters of the driveline that affect various operating states. The method to estimate state parameters for the aforementioned powertrain system includes monitoring operating rotational speed for each of the torque-generative devices, in this case Motor A  56 , Motor B  72 , and engine  14 . The engine output speed, NE, is measured at shaft  18 , and transmission input speed, N 1 , is measured at shaft  12 . Output rotational speed, No, of the transmission  10  at shaft  64  is measured. Torque commands from the control system to the torque-generative devices are determined and referred to as T A , T B , and T E . A plurality of driveline torque loads are also determined and used as input. The aforementioned mathematical model equations are executed in one of the controllers to estimate each state parameter, including T DAMP , T AXLE , N A , N B , N O , N E , N WHL , using as inputs: the operating speed for each of the torque-generative devices, the output speed of the transmission device, the torque commands to the torque-generative devices, and the torque loads. The distributed controller architecture described with reference to  FIG. 2 , and the algorithmic structure described herein is executed in a manner that causes estimation of the aforementioned state parameters to be achieved in real-time, i.e. calculation of each estimated state occurs during a single clock cycle of the controller so there is limited or no lag time in determining the various states, thus eliminating or minimizing potential for loss of control of the system. Input parameters to the driveline dynamics estimator  240  include motor torque values, T A  and T B , engine torque T E , clutch torques T CL     —     N , to clutches C 1 , C 2 , C 3 , C 4 , brake torque T BRAKE , accessory load T ACC , and road load, T RL , and the transmission operating mode. The mathematical model equations are applied to the aforementioned inputs to dynamically calculate estimated output state parameters of the driveline, including T DAMP     —     EST , T AXLE     —     ES T, N A     —     EST , N B     —     EST , N o     —     EST , N E     —     EST , and N WHL , based upon the input parameters. A first speed matrix comprising the estimated speeds N A     —     EST , N B     —     EST , N o     —     EST , N E     —     EST , N WHL     —     EST  is subtracted from a second speed matrix comprising measured speeds N A , N B , N o , N E , N WHL  output from driveline dynamic control  230 . The resultant matrix is input to an estimator  232 , wherein it is multiplied by one of a plurality of gain matrices, to determine a matrix of estimated state corrections. Each of the gain matrices comprises a matrix of scalar gain factors, preferably determined for each transmission operating mode, i.e. the specific operating mode and gear configuration, described hereinabove with reference to Table 1. In this embodiment the gain matrices are determined off-line, and stored as calibration values in one of the on-board controllers. There are preferably at least two sets of gain matrices developed and executed as part of the estimator feedback gain  232  action, wherein one set is for use when the driveline is in a neutral lash state, and one set is for use when the driveline is in a drive state.  
         [0055]     The matrix of estimated state corrections is used as feedback by the driveline dynamics estimator  240  in determining the dynamically calculated estimated output states of the driveline, including T DAMP     —     EST , T AXLE     —     EST , N A     —     EST , N B     —     EST , N o     —     EST , N E     —     EST , N WHL     —     EST  based upon the input parameters. When the first speed matrix comprising the estimated speeds is equal to the second speed matrix comprising measured speeds, it is determined that the outputs of the estimator, comprising T DAMP     —     EST , T AXLE     —     EST , N A     —     EST , N B     —     EST , N 0     —     EST , N E     —     EST , N WHL     —     EST  are accurate measurements of actual operating states of the driveline.  
         [0056]     Referring now to  FIGS. 5 and 6 , a method to control torque transmitted from the powertrain system described with reference to  FIGS. 1 and 2  during transitions that can result in driveline jerks is described in detail. The controlled torque, T AXLE , is transmitted to the axle  92  of the driveline. The method and system described herein are executed as one or more algorithms in the distributed controller architecture shown with reference to  FIG. 2 , and utilizes the multivariate feedback control scheme described with reference to  FIG. 3 , including parameter state estimation described with reference to  FIG. 4 , each incorporated by reference, as detailed hereinabove.  
         [0057]     The method to control driveline torque originating in the powertrain system which has the torque-generative devices  14 ,  56 ,  72 , operable to transmit motive torque to the transmission comprises determining a desired axle torque, T AXLE     —     DES , and determining output speeds of the powertrain N o , and driven wheel, N WHL  of the driveline. Each of the torque-generative devices  14 ,  56 ,  72  is controlled using the aforementioned and referenced multivariate control system, based upon a time-rate change in the desired axle torque, T AXLE     —     DES     —   dot. The torque-generative devices are driven, and limited in operation based upon the time-rate change in desired axle torque, T AXLE     —     DES     —   dot when the output speed of the driven wheel, N WHL  is less than a predetermined value, typically from a zero speed launch. This time-rate change may be further controlled based upon the time-rate change in desired axle torque, which includes a transition of one of the motor/generators between a torque-generative mode and an electric-generative mode. This includes controlling driveline torque, T AXLE     —     DES  during vehicle launch, and controlling driveline torque T AXLE     —     DES  during a change in gear ratio of the transmission  10 .  
         [0058]     The following parameters are determined: powertrain torque transmitted to the driveline, i.e. T AXLE , output speed of the transmission, N o , to the driveline, and driven wheel speed, N WHL . A lash state is determined, and each of the torque-generative devices of the powertrain is controlled based upon the lash state. In this embodiment, the lash state is determined using an estimator  250 , which preferably comprises an algorithm within one of the controllers. Inputs to the lash state estimator  250  include estimated axle torque, T AXEL     —     EST , estimated output speed, N o     —     EST  of the transmission, and estimated driven wheel speed, N WHL     —     EST , each which is output from the driveline dynamics estimator  240 . The lash state estimator  250  is operable to compare the estimated axle torque, T AXLE     —     EST  and estimated output speed, N o     —     EST  to determine the lash state to be one of a positive state, a negative state, or a neutral state. The positive state is indicated when the estimated axle torque, T AXLE     —     EST  and estimated output speed, N o     —     EST  and estimated driven wheel speed, N WHL     —     EST , show torque being transmitted from the transmission through the driveline in a forward direction, i.e. when the vehicle is driven in a forward motion. The negative state is indicated when the estimated axle torque, T AXLE     —     EST  and estimated output speed, N o     —     EST  and estimated driven wheel speed, N WHL     —     EST , show torque being transmitted from the transmission through the driveline in a negative direction, i.e. when the vehicle is driven in a reverse motion, or when there is a powertrain braking and regeneration mode. The neutral state is indicated when there is no torque being transmitted to the driven wheels through the driveline from the transmission.  
         [0059]     When output of the lash state estimator indicates a positive lash state or a negative lash state, no action occurs in the control system based upon the lash.  
         [0060]     When output of the lash state estimator indicates a neutral state, the resultant matrix comprising the aforementioned difference between the first estimated speed matrix (comprising N A     —     EST , N B     —     EST , N O     —     EST , N E     —     EST , N WHL     —     EST ) and the second measured speed matrix (comprising N A , N B , N O , N E , N WHL ) is multiplied by one of a plurality of lash gain matrices, to determine a matrix of estimated state corrections for lash operation. When the matrix of estimated state corrections for lash operation is used in the driveline dynamics estimator  240 , the resultant outputs of the estimator  240 , comprising T DAMP     —     EST , T AXLE     —     EST , N A     —     EST , N B     —     EST , N 0     —     EST , N E     —     EST , N WHL     —     EST , are provided as feedback to the multivariate motor damping control  220 . The multivariate motor damping control  220  uses the estimator outputs to dampen actual axle torque output, T AXLE  during the period of time in which the neutral lash state is detected. Thus, the torque transmitted to the driveline, T AXLE  is less than operator-commanded torque, T AXLE     —     DES  when the lash state is neutral. When the lash state subsequently becomes either positive or negative, use of the lash gain matrices is discontinued, and a gain matrix is selected as previously described with reference to  FIG. 4 .  
         [0061]     Referring now to  FIG. 6 , exemplary results are shown for management of axle torque during a period when a potential for driveline jerk may occur. Driveline jerk is defined as a rate of change of axle torque due to a step-change in desired axle torque, such as results from operator input to the UI  13 . Such changes typically occur during vehicle launch, and other points of acceleration. Driveline jerk may also occur due to a transition in operating mode of one of the motor/generators  56 ,  72 , e.g. between a torque-generative mode and an electrical energy generative mode. A typical constraint in magnitude of jerk, driven by operator expectations, comprises a peak jerk, or acceleration, of less than 1.6 G/sec. In this instance, desired axle torque, T AXLE     —     DES , is determined based upon operator inputs, and adjusted with filtering constants executed in the desired dynamics scheme  210 . The torque limitation is preferably accomplished by controlling damping torque values for Motor A and Motor B, T A     —     DAMP  and T B     —     DAMP , calculated with reference to the multivariate motor damping torque control  220 , previously referenced and described. The multivariate motor damping control  220  uses the estimator outputs to dampen actual axle torque output, T AXLE . Thus, the torque transmitted to the driveline, T AXLE  is less than operator-commanded torque, T AXLE     —     DES  when the desired axle torque is jerk-limited. In this manner the multivariate feedback control scheme is useable to manage and suppress magnitude and occurrence of driveline clunks or jerks.  
         [0062]     Input parameters to the driveline dynamics estimator  240  include motor torque values, T A  and T B , engine torque T E , clutch torques T CL     —     N , to clutches C 1 , C 2 , C 3 , C 4 , brake torque T BRAKE , accessory load T ACC , and road load, T RL , and the transmission operating mode. The mathematical model equations are applied to the aforementioned inputs to dynamically calculate estimated output state parameters of the driveline, including T DAMP     —     EST , T AXLE     —     EST , N A     —     EST , N B     —     EST , N 0     —     EST , N E     —     EST , N WHL     —     EST , based upon the input parameters. The first speed matrix comprising the estimated speeds is subtracted from the second speed matrix comprising measured speeds, as previously described. The resultant matrix is multiplied by one of a plurality of gain matrices, to determine the matrix of estimated state corrections. Each of the plurality of gain matrices comprises a matrix of scalar gain factors, preferably determined for each transmission operating mode, i.e. the specific operating mode and gear configuration, described hereinabove with reference to Table 1. In this embodiment the gain factors are determined off-line, and stored as calibration values in one of the on-board controllers. There are preferably at least two sets of gain matrices developed and executed as part of the estimator feedback gain  232  action, wherein one set is for use when the driveline is in a neutral lash state, and one set is for use when the driveline is in a drive state.  
         [0063]     The matrix of estimated state corrections is used as feedback by the driveline dynamics estimator  240  in determining the dynamically calculated estimated output states of the driveline, including T DAMP     —     EST , T AXLE     —     EST , N A     —     EST , N B     —     EST , N 0     —     EST , N E     —     EST , N WHL     —     EST  based upon the input parameters. When the first speed matrix comprising the estimated speeds is equal to the second speed matrix comprising measured speeds, it is determined that the outputs of the estimator, comprising T DAMP     —     EST , T AXLE     —     EST , N A     —     EST , N B     —     EST , N 0     —     EST , N E     —     EST , N WHL     —     EST  are accurate measurements of actual operating states of the driveline.  
         [0064]     Although this embodiment has been described as controlling output of the electric motors, it is understood that alternate embodiments of this invention can include control schemes which are operable to control the torque output of the internal combustion engine as well as the electric motors. It is further understood that some or all of the estimated values for torque and speed can instead be monitored directly with sensors and sensing schemes.  
         [0065]     The invention 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 invention.