Abstract:
A method of distributing a torque demand in a hybrid electric vehicle having an internal combustion engine  200  and an electric motor  202  is provided. In hybrid operation, the motor  202  initially starts the vehicle. When the vehicle desired power demand reaches a first vehicle  27 . A method as described in claim 26, wherein said third predefined percentage of accelerator pedal travel position is 0%.operational parameter, a controller  214  switches the torque demand to the engine  200.  An accelerator pedal  220  has a position sensor  222  which determines a non-fixed pedal  220  first position during transition between the motor  202  and engine  200.  The accelerator pedal  220  also has a preset second position wherein a maximum of engine  200  torque is requested. The controller  214,  cognizant of the accelerator pedal  220  first and second positions, linearly scales the accelerator pedal  220  to provide a uniform torque-responsive accelerator pedal.

Description:
BACKGROUND OF INVENTION  
         [0001]    The present invention relates to a hybrid electric vehicle having an electric motor (s) and an internal combustion (IC) engine and a method of control thereof. More particularly, the present invention provides the hybrid electric vehicle with an accelerator pedal which commands torque from either the IC engine or the electric motor in a manner which is essentially non-perceptible to the driver from the operation of an accelerator pedal on a conventional vehicle powered by an IC engine.  
           [0002]    The primary objective of the automobile industry is the development of safe vehicles for personal mobility that meet or exceed customer expectations for performance, including acceleration, braking, maneuverability, and comfort, while minimizing the impact on the environment.  
           [0003]    The automobile is an integration of many complex nonlinear systems, one of which is the powertrain system. A conventional vehicle powertrain consists of an IC engine, transmission, and driveline including a differential and axle system(s) with drive wheels. An electric vehicle powertrain consists of an electric motor, gearing, and driveline including a differential and axle system with drive wheels. Also included are accessories and peripherals connected to the powerplant such as power steering, power brakes, and air conditioning. The vehicle powertrain is a composition of electrical, mechanical, chemical, and thermodynamic devices connected as a nonlinear dynamic integrated system, with the primary objective of providing the power source for transportation.  
           [0004]    Essential to the control of any vehicle is the accelerator pedal. The accelerator pedal does not directly control velocity but rather controls a torque demand to the vehicle power train. Accordingly, when the driver of the vehicle wishes to increase their velocity, the accelerator pedal is actuated to place a torque demand upon the vehicle power train. A torque response to the torque demand is a function of many different variables. For a conventional automotive vehicle powered by an IC engine, torque output at the wheels of the vehicle is related to gear ratios of the transmission and the transaxle; engine RPM, engine compression ratio; throttle setting, intake air temperature; emission system performance; valve operation; and ignition system performance. The engine and drive train controllers accommodate the various variables such that the torque output to the driver is mainly a function of a tactile experience foot maneuvering of the accelerator pedal.  
           [0005]    The need to reduce fuel consumption and emissions in automobiles and other vehicles predominantly powered by IC engines is well known. Vehicles powered by electric motors attempt to address these needs. Another alternative solution is to combine a smaller IC engine with an electric motor or motors into one vehicle. Such a vehicle combines the advantages of an IC engine vehicle and an electric vehicle and is typically called a hybrid electric vehicle (HEV). See generally, U.S. Pat. No. 5,343,970 z (Severinsky).  
           [0006]    HEVs have been described in a variety of configurations. Many HEV patents disclose systems where an operator is required to select between an electric and IC operation. In other configurations, the electric motor drives one set of wheels and the IC engine drives a different set of wheels.  
           [0007]    Other HEV configurations have been provided wherein the internal combustion engine and the electric motor power a common drive axle. Some configurations wherein the electric motor and IC engine power a common drive axle are referred to as parallel hybrid electric vehicle (PHEV) configurations. One PHEV configuration has an engine and two traction motors utilized to power a common drive axle and the power train of the system has both the engine and the motors on a common side of the differential for the drive axle.  
           [0008]    In another configuration commonly referred to as a post-transmission design, an IC engine is connected with a transmission and differential via an engine clutch. An electric motor is torsionally connected with the differential by a separate motor clutch. The post-transmission parallel hybrid power train accordingly can be powered exclusively by the engine or the electric motor or by both power sources simultaneously.  
           [0009]    A vehicle that provides torque to a common or different drive axles through two power sources must be able to partition the torque to the two power sources such that fuel economy and emissions are optimized. In addition, the distribution of torque must be invisible to the driver. The driver commands torque through the accelerator pedal and this amount must be determined. It is desirable that this determined torque request be distributed to the power sources in such a way that the car always behaves in a same manner. However, the controller determines to demand torque from the engine or the motor based upon 20 or 30 operational parameters many of which are non-linear. The controller must consider how to distribute torque in order to maximize fuel economy, extend battery life and range, minimize vehicle emissions and at the same time provide an acceptable driving performance for the vehicle. Many of these factors that are considered by the engine controller are non-linear with respect to the torque demanded at the drive axle.  
           [0010]    Further complicating the torque distribution matter is the fact that the amount of torque available from the electric motor is a function of the state of charge (SOC) of the HEV&#39;s batteries. If the HEV battery has a low state of charge, the torque available from the motor will be low. Conversely, if battery charge is high, torque demand from the motor may be at its maximum. U.S. patents discussing these and other issues related to HEV torque output are U.S. Pat. Nos. 5,549,172; 5,899,286; 5,935,040; and  
           [0011]    [0011] 6 , 064 , 934 .  
           [0012]    Experience has shown that in most situations it is preferable to start an HEV forward from a rest position utilizing the electric motor. Electric motors differ from IC engines in that their maximum torque output is essentially available from a rest position, unlike an IC engine which must reach a predefined high RPM output. When the power demand upon the vehicle reaches a certain level, it is usually preferable to thereafter rely upon torque generation from the IC engine. Periods of braking the vehicle allow the vehicle to charge the batteries using regenerative braking. When traveling at highway speeds and attempting to pass another vehicle where wide open throttle conditions exist, typically both power plants will be run to their maximum capacities.  
           [0013]    Considering the aforementioned factors, further complicated by switching gear ratios and other operating conditions, it is essential that the torque output or pedal feel at the accelerator pedal be as constant as possible so that the operator of the vehicle can drive the vehicle with confidence in a manner that he or she is used to in driving conventional vehicles powered by an IC engine alone.  
           [0014]    Accordingly, it is desirable to provide a HEV which can be powered at various times by the motor, IC engine alone or with the use of both power plants while at the same time providing a constant pedal feel.  
         SUMMARY OF INVENTION  
         [0015]    To make manifest the above noted desire, a revelation of the present invention is brought forth. In a preferred embodiment the present invention provides a HEV and method of operation thereof where the vehicle is powered by an electric motor and an IC engine. The vehicle is initially powered by the electric motor up to a first vehicle operational parameter level. Typically, the vehicle operational parameter level will be a combination of variables highly dependent upon the power level of the vehicle. Above the first vehicle operation parameter level, the vehicle will be powered by an IC engine. At the time of the transition between the electric motor and the IC engine, a determination will be made of the torque level of the motor. Another determination will be made of the accelerator travel position. A predefined percentage of a maximum IC engine torsional output will be fixed to a predefined accelerator pedal travel second position. Typically, the predefined percentage of maximum engine torsional output will be 100% and the predefined accelerator pedal travel second position will be between 75 and 85% and is commonly placed at the 80% position. The accelerator pedal travel second position is often referred to as a tip in value of the accelerator pedal. The vehicle controller will scale the accelerator travel by a predefined functional relationship from the accelerator pedal travel first position to the accelerator pedal travel second position. In most instances, the predefined functional relationship will be linear. Accordingly, and in most instances, the accelerator pedal travel will be scaled such that at 80% of travel, maximum engine torque will be demanded via the accelerator pedal. Torque demand beyond the 80%, sometimes referred to as boost torque position, flooring the pedal or wide open throttling position of the accelerator pedal, will cause the electric motor to additionally provide torque to the drive axle typically in a preferred linear manner.  
           [0016]    It is an advantage of the present invention to provide a HEV which distributes torque to an IC engine and electric motor in a manner which causes operation of the vehicle to be similar to that of a conventional IC engine powered vehicle by use of an accelerator pedal.  
           [0017]    Other advantages of the invention will become more apparent to those skilled in the art upon a reading of the following detailed description and upon reference to the drawings. 
       
    
    
     BRIEF DESCRIPTION OF DRAWINGS  
       [0018]    FIGS.  1 - 9  are block diagrams of the torque distribution algorithm utilizing a preferred embodiment hybrid electric vehicle according to the present invention  
         [0019]    [0019]FIG. 10 is a view of a post-transmission hybrid electric vehicle power train utilized in the algorithm described in FIGS.  1 - 9 .  
         [0020]    FIGS.  11 A-J through  17 A-J are graphic displays of the functional response of the hybrid electric vehicle which is controlled by the algorithm shown in FIGS.  1 - 9  which give graphic displays of vehicle velocity (A), throttle angle (B), engine RPM (C), transmission gear ratio (D), torque output at the half shafts (E), engine torque (F), motor torque (G), percentage of accelerator pedal travel (H), velocity error (I) and engine clutch engagement (J). 
     
    
     DETAILED DESCRIPTION  
       [0021]    [0021]FIG. 10 is a diagram of a post-transmission PHEV configuration. A powertrain driveline  197  includes rotational dynamics for a PHEV, which accepts IC engine  202  and motor torque (in a regenerative or motoring mode), and delivers torque to drive wheels  204  through a differential  206  and halfshafts  208 . Motor torque is delivered via a transaxle to the differential  206  through a 4×4 coupler connected to a halfshaft  208 , and summed with engine torque at the differential  206 . The engine  200  is connected directly to the differential  206  through the engine clutch  210 , transmission and final drive, as in a conventional powertrain. Included in the driveline  197  is a layshaft transmission  212  that lies between the engine clutch  210  and the differential  206 .  
         [0022]    A PHEV coordinated controller  214  provides motoring and regenerative commands to a motor controller  215  for corresponding positive and negative motor  202  torque, and throttle blade commands to an engine controller  217 . These commands may be based on the battery SOC, motor speed versus torque limits, motor  202  torque current, motor  202  field current, transmission  212  gear, accelerator pedal  220  position, engine clutch  210  state, motor clutch  225  state, engine  200  speed, average power at the drive wheels  204 , shift status, estimated engine  200  torque, and estimated motor  202  torque available. In addition, the controller  214  provides engine and motor clutch  210 ,  225  control during braking, or hybrid operation. The controller distributes braking commands to a regenerative brake system associated with the motor  202  and a friction brake system (not shown).  
         [0023]    The torque may be partitioned to operate in an engine  200  only mode, a motor  202  only mode, or a two traction device mode (hybrid mode). Hybrid mode operation consists of motor  202  only operation, engine  200  operation, motor  202  torque application during shifting, motor  202  assist during power boost, and regenerative braking. The motor  202  can provide torque during shifting so that torque disruption to the driveline  197  is eliminated. The drive line  197  will provide negative torque via the motor  202  during braking for energy recovery to a battery  213 . During periods of low storage device (SOC) battery  213  operation, the engine  200  may be loaded with the alternator (not shown) to increase the storage device operation. The vehicle driveline  197  has a torque sensor  216 . Torque sensor  216  may be a single torque sensor or a plurality of torque sensors which may sense the torque at the halfshafts  208  and by computation determine the torque of the engine  200  or of the motor  202  or may be a combination of sensors appropriately placed. The controller  214  is also connected with a motor torque available sensor  218  to apprise the controller  214  on the amount of maximum motor torque available which is typically highly dependent upon battery SOC. To receive operator drive commands for torque there is an accelerator pedal  220 . The accelerator pedal  220  is operatively associated with an accelerator pedal position sensor  222 . The accelerator pedal position sensor  222  is also communicative with the controller  214 . The motor  202  also has between itself and the differential  206  a clutch  225  which for the purposes of this invention can be considered essentially in a closed or engaged position. The vehicle also has a brake pedal  224  which communicates with the controller  214 .  
         [0024]    The vehicle launches in motor  202  only mode for optimal drivability, emissions, and fuel economy. When the average power at the vehicle drive wheels  204  reaches a level where operation of the engine  200  is beneficial, the motor  202  is no longer operated alone.  
         [0025]    Overview.  
         [0026]    This section contains a high level description with a detailed description in the next section. The Torque Split 1 control algorithm determines the magnitudes of the motor  202  torque command and the engine  200  torque command. This algorithm also determines the accelerator pedal  220  command from the driver and determines the torque partitioning between the traction devices (engine  200 , motor  202 ). FIGS.  1 - 8  are block diagrams depicting the control algorithm. These diagrams were used to generate autocode (C code), which actually ran in the prototype vehicle.  
         [0027]    [0027]FIG. 1: Block Diagram of Torque Distribution Algorithm.  
         [0028]    This algorithm contains seventeen inputs as labeled in FIG. 1:  
         [0029]    Motor 202 TQEstimate (Nm): estimated motor  202  torque.  
         [0030]    BRAKE SWITCH (logic): when 1, a brake pedal  224  is depressed  
         [0031]    ACCEL POS: accelerator pedal travel position in per unit values (0—no pedal command to 1—wide open throttle (WOT))  
         [0032]    TeMAXavailATwheels  204  (Nm): Maximum Engine  200  Torque Available at the Wheels  204   
         [0033]    accel pedal flag (logic): when 1, the accelerator pedal  220  is depressed  
         [0034]    mtr only trigger (logic): motor  202  only trigger=1, only the motor  202  is operating, no engine  200  operation  
         [0035]    TeATwheels  204  (Nm): Engine  200  Torque at the Wheels  204   
         [0036]    engine  200  on c (logic): when 1, the engine  200  is operating with or without the motor  202   
         [0037]    engine  200  on and shift b (logic): when 1, the engine  200  is operating without motor  202  boost prior to the shift  
         [0038]    mo assist no sh eng on d (logic): when 1, the motor  202  is boosting and the vehicle is not shifting  
         [0039]    GEAR RATIO  
         [0040]    motor  202  only flag a (logic): when 1, the motor  202  is operating without the engine  200   
         [0041]    motor  202  assist with shift flag e (logic): when 1, the motor  202  is boosting prior to a shift  
         [0042]    TmATwheels  204 MAX (Nm): Maximum Motor  202  Torque Available at the Wheels  
         [0043]    ACTUAL GEAR: R,N, 1,2,3,4,5  
         [0044]    CLU POS: clutch  210  position logic, when 1, the engine clutch  210  is asked to engage  
         [0045]    clutch  210  state (logic): when 1, the engine clutch  210  is engaged  
         [0046]    This algorithm contains two outputs as labeled in FIG. 1:  
         [0047]    Te cmd at engine  200  (Nm): torque command at the engine  200   
         [0048]    Tq cmd at motor  202  (Nm): torque command at the motor  202   
         [0049]    When the vehicle is launched in motor  202  only mode, depicted in FIG. 2, the amount of motor  202  torque commanded is a linear function based on the maximum motor  202  torque available at any instant, TmATwheels 204 MAX, and the percentage of accelerator pedal  220 , ACCEL POS, depressed. This is labeled as perACCpedal Tmavail, block  95 , in FIG. 2. If the accelerator pedal  220  is depressed 100%, then 100% of the maximum motor  202  torque available is commanded. If the accelerator pedal  220  is depressed 50% then the motor  202  torque commanded is 50% of the maximum motor  202  torque available. Since the battery  213  SOC can change drastically from the beginning of a journey to the end of a journey, the accelerator pedal  220  is scaled in this manner so that the driver always can be assured of receiving more motor  202  torque for increased pedal depression. The amount of motor  202  torque available is heavily dependent on the battery  213  SOC. When the driver depresses the accelerator pedal  220  50%, the driver knows 50% more torque is available if needed. If the driver depresses the accelerator pedal  220  100% and the vehicle does not accelerate as desired due to low battery  203  SOC the driver knows to drive cautiously.  
         [0050]    This vehicle is capable of operating in a motor  202  only, engine  200  only or hybrid mode. This mode is selected by the driver through a switch on the driver control panel. Any mode that the driver chooses to operate the vehicle is transparent. The pedal interface between the driver and the vehicle is invisible to the driver.  
         [0051]    When the vehicle is operated in the hybrid mode and the vehicle transitions from motor  202  only mode to engine  200  on mode, the torque commanded by the driver at this transition is commanded initially to the motor  202 . If the driver”s accelerator pedal  220  command did not change but the hybrid controller wishes to command torque to the engine  200  instead of the motor  202  the driver will not be aware of this transition.  
         [0052]    When the vehicle transitions from motor  202  only to engine  200  on operation the motor  202  torque commanded must be saved at the exact accelerator pedal  220  position command from the driver during the transition, shown in FIGS. 3 and 4. This saved motor  202  torque command, TmATwheels 204 SAVE, and pedal travel (first position), motor 202 perACCpedalSAVE, is then used to scale the accelerator pedal”s torque output per pedal angular movement. A predefined fixed percentage of pedal travel is selected as a second pedal position (second position). Preferably the percentage of pedal travel selected as the second position will be 75-85%. 80% pedal travel has been found to be a preferable pedal travel second position in many instances. A first predefined percentage of a maximum of engine  200  torque available at the wheels  204  corresponds to 80% accelerator pedal  220  travel (second position). The first predefined percentage of maximum engine  200  torque available will typically be between 95 and 100%. 100% has been found to be preferable in most instances. The difference between 80% of pedal travel (second position) and the saved percentage of pedal travel first position is used as endpoints. A first predefined function relationship, which is typically linear is used to scale the accelerator pedal  220  with the maximum engine  200  torque being at the accelerator pedal  220  second position. This is depicted in FIG. 5.  
         [0053]    At 80% of accelerator pedal  220  travel, the maximum engine  200  torque available is commanded. The remaining 20% of pedal travel is scaled as a second predefined function, typically linear with a second predefined percentage of maximum motor  202  torque available (typically 100%) to provide boost. At 80% accelerator pedal  220  travel no motor  202  torque is commanded, and at 100% accelerator pedal  220  travel the second predefined percentage maximum motor  202  torque available is commanded.  
         [0054]    As the vehicle transitions from engine  200  operation back to motor  202  only operation, the engine  200  torque commanded at the transition and the non-fixed accelerator pedal  220  travel position (third position) at the transition are saved. These saved values are used to scale the motor  202  torque command in a third predefined functional relationship (usually linear) between the accelerator pedal  220  third position and a third predefined percentage of pedal travel position (typically 0-5%). This is shown in FIGS. 6 and 7.  
         [0055]    Motor  202  Torque Command.  
         [0056]    The vehicle launches in motor  202  only mode. The amount of motor  202  torque commanded, Tq cmd at mtr, is described in FIG. 2. The following explains the motor  202  torque command algorithm. The motor  202  torque commanded at the motor  202  is that motor  202  torque commanded at the wheels  204  divided by the 4×4 and transaxle gear ratios, block  19 , and filtered with a low pass filter, blocks  92  and  94 . If the brake switch, activated by brake pedal  224 , is high the torque command at the motor  202 , Tq cmd at mtr, is zero in this part of the algorithm, blocks  2  and  8 . If the engine  200  clutch  210  is being commanded to engage (CLU POS=1) and the clutch  210  is open (clutch  210  state=0) and the transmission is in second gear blocks  80 ,  3 ,  11 ,  97 , then the motor  202  torque commanded at the wheels  204  is  30  Nm*4×4 and transaxle gear ratios, block  1 .  
         [0057]    If the motor  202  only flag a, or the motor  202  assist with shift flag e or the engine  200  on and shift b flags are high, blocks  16  and  5 , then the motor  202  torque commanded at the wheels  204 , Tm cmd at wheels  204 , is the acceleration position, ACCEL POS, multiplied by the maximum motor  202  torque at the wheels  204 , TmATwheels 204 MAX, block  95 . Else if the motor  202  assist with no shift d is high, block  86 , then the motor  202  torque commanded at the wheels  204  is the difference between the present accelerator pedal  220  position, ACCEL POS, and 80% of the pedal travel multiplied by the maximum motor  202  torque available at the wheels  204 , TmATwheels 204 MAX, divided by 20% of the pedal travel, block  83 .  
         [0058]    Else if the motor  202  only flag a is high after previously being in a state where motor  202  only flag a, or motor  202  assist with shift flag e, or engine  200  on and shift flag b, or motor  202  assist with no shift flag d, block  7 , was high then the motor  202  torque command at wheels  204  is the acceleration position, ACCEL POS, multiplied by the engine  200  torque at the wheels  204  saved, TeATwheels 204 SAVE, divided by the engine  200  torque percent accelerator pedal  220  saved, TeperACCpedalSAVE. This is shown in FIG. 8, blocks  10  and  97 .  
         [0059]    Motor  202  to Engine  200  Transition Saved Torque and Pedal Values.  
         [0060]    As depicted in FIGS. 3 and 4, when the BRAKE SWITCH is high, the accelerator position ACCEL POS is continuously being updated and the motor 202 perACCpedalSAVE is zero. When the BRAKE SWITCH goes low the ACCEL POS accelerator position is no longer updated and the present value is saved as motor 202 perACCpedalSAVE. Similarly, TmATwheels 204 SAVE is saved. When the BRAKE SWITCH is low then motor 202 perACCpedalSAVE is zero. When the BRAKE SWITCH goes high, then the accelerator position is saved as motor 202 perACCpedalSAVE and the motor  202  torque is saved as TmATwheels 204 SAVE.  
         [0061]    Engine to Motor Transition Saved Torque and Pedal Values.  
         [0062]    As depicted in FIGS. 6 and 7, when the mtr only trigger is high the accelerator position ACCEL POS is continuously being updated and the TeperACCpedalSAVE is zero. When the mtr only trigger goes low the ACCEL POS accelerator position is no longer updated and the present value is saved as TeperACCpedalSAVE. Similarly, TeATwheels 204 SAVE is saved. When the mtr only trigger is low then TeperACCpedalSAVE is zero. When the mtr only trigger goes high, then the accelerator position is saved as TeperACCpedalSAVE and the engine  200  torque is saved as TeATwheels 204 SAVE.  
         [0063]    Engine  200  Torque Command.  
         [0064]    As described in FIG. 8, when the vehicle is not in a motor  202  only mode, the engine  200  torque command, Te cmd, is derived by subtracting the percent of motor  202  only accelerator pedal  220  saved, motor 202 perACCpedalSAVE, from the present accelerator pedal  220 , ACCEL POS, value. This difference is the amount of extra pedal desired, amt of extra desired, from the driver. The amount of extra desired is that above and beyond what was previously being commanded during motor  202  only.  
         [0065]    During the transition from motor  202  to engine  200  on, as shown in FIG. 5, the difference between the maximum engine  200  torque available at the wheels  204 , TeMAXavailATwheels 204 , and the motor  202  torque saved, TmATwheels 204 SAVE, at the wheels  204  gives the engine  200  torque available for scaling, TeAVAILscaled Nm, block  4 . The difference between the 80% tip in value and the percent motor  202  accelerator pedal  220  saved, motor 202 perACCpedalSAVE, determines the available percentage of the pedal for scaling, block  1 , 7 , 9 . The engine  200  torque available, TeAVAILscaled Nm, multiplied with the amount of extra accelerator pedal  220  desired divided by the percent of accelerator pedal  220  scaled, perPEDALavailSCALED, gives the engine  200  torque commanded referred to the wheels  204 , TeCMDatWHEELS 204 , block  3 . The absolute value of the engine  200  torque commanded at the wheels  204  is taken, ABS_Te_CMD, and multiplied by the sign of the amount of extra accelerator pedal  220  desired, amt of extra desired. The motor  202  torque saved at the wheels  204 TmATwheels 204 SAVE, is then added to the signed engine  200  torque command, ABS_Te_CMD, when the accelerator pedal  220  is depressed to get TeCMD for POS scaling, blocks  94 ,  98 , and  99 .  
         [0066]    In FIG. 8, when the amount of extra (torque) desired is negative, block  35 , the accelerator position, ACCEL POS, is less than the torque motor  202  per accelerator pedal  220  saved, motor 202 perACCpedalSAVE. When this occurs, the present accelerator position, ACCEL POS, is multiplied by the motor  202  torque saved at the wheels  204 , TmATwheels 204 SAVE, and divided by the percent motor  202  accelerator pedal  220  saved, motor 202 perACCpedalSAVE, block  25 . This then is the engine  200  torque command, Te cmd, else the previous engine  200  torque command, TeCMDfor POSscaling, is used, block  45 .  
         [0067]    Viewing FIG. 9, if the transmission is in neutral, then the engine  200  torque command is zero, blocks  93 ,  96 , and  97 . The engine  200  torque command at the engine  200  becomes the engine  200  torque commanded at the wheels  204  divided by the gear ratio and the final drive, blocks  9  and  94 . If a motor  202  assist non shifting mode, block  9 , is desired then the maximum engine  200  torque available at the wheels  204  is commanded, TeMAXavailATwheels 204 . This occurs when the accelerator pedal  220  position is greater than 80%. If the engine  200  is on without shifting then, Te cmd is the engine  200  torque command, Te cmd, at engine  200 .  
         [0068]    A post-transmission PHEV was built and test data was taken. The vehicle was driven in engine  200  only mode, motor  202  only mode and hybrid mode, while test data was taken.  
         [0069]    The following figures show simulations of medium acceleration hybrid operation; low acceleration/deceleration profile repeated on a 10% grade hybrid operation; low acceleration/deceleration profile repeated in hybrid operation; medium acceleration/deceleration profile repeated in hybrid operation; WOT acceleration/deceleration profile repeated in hybrid operation. The figures also show medium acceleration engine  200  only and low acceleration motor  202  only simulations.  
         [0070]    The hybrid mode simulations show strip charts of vehicle velocity in mph, throttle angle in degrees, engine  200  speed in rpm, gear number, halfshaft torque in Nm, engine  200  torque in Nm, motor  202  torque in Nm, accelerator position in per unit, velocity error between the command and vehicle in mps, and clutch  210  position in per unit. The engine  200  only and motor  202  only simulations show strip charts of vehicle velocity in mph, throttle angle in degrees, engine  200  speed in rpm, gear number, halfshaft torque in Nm, and engine  200  torque in Nm.  
         [0071]    Medium Acceleration Hybrid Operation.  
         [0072]    The first plot, FIG. 11, shows a medium acceleration hybrid operation. The vehicle launches in motor  202  only mode. From zero seconds until 2.5 seconds the vehicle begins to accelerate, the throttle angle is at idle, the engine  200  speed is at idle speed, the vehicle is in first gear, the halfshaft torque begins increasing, the engine  200  torque is zero, the motor  202  torque is increasing, the accelerator position is increasing from 20% to maximum, the velocity error is increasing and the clutch  210  is disengaged. From about 2.5 seconds until about 6 seconds the vehicle is in second gear.  
         [0073]    During second gear operation the vehicle continues to accelerate, the throttle angle increases from idle during the gear shift (as seen in the first second of second gear) to full throttle; the engine  200  speed increases from idle speed to 5000 rpm; the halfshaft torque remains constant during the first second in second gear, due to torque fill in from the motor  202  during the gear shift, the halfshaft torque then increases due to the engine  200  torque being added to the motor  202  torque; the engine  200  torque starts at idle during the gear shift, and then ramps to 100 Nm of torque; the motor  202  torque provides fill in torque at the beginning of the shift, and is then ramped to an appropriate boost value to aid the engine  200  during the driver WOT command; the velocity error decreases as the engine  200  assists the motor  202  in second gear; the clutch  210  is beginning to engage.  
         [0074]    The shift from second to third gear occurs at about seven seconds. During the gear shift the vehicle continues to accelerate due to the motor  202  torque fill in; the throttle angle is ramped to idle; the engine  200  speed is ramped to idle, but does not make it to idle before clutch  210  engagement occurs; gear three is selected; the halfshaft retains torque due to the motor  202  torque fill in during a shift; the vehicle velocity error continues to decrease; the clutch  210  is disengaged. From seven until nine seconds gear three is exercised. During gear three the motor  202  torque can be seen decreasing due to the driver accelerator command falling below 80%, that is it exits the boost mode. The vehicle velocity error is almost zero. The vehicle shifts to fourth and fifth gear in the same manner.  
         [0075]    Repeated Low Acceleration/Deceleration on a 10% Grade Hybrid Operation.  
         [0076]    The vehicle launches in the same manner during this mode of operation. In FIG. 12, during second gear the motor  202  does not assist the engine  200  due to a less than 80% driver accelerator command. During third gear motor  202  assistance is necessary due to the driver commanding more than 80% throttle. During fourth gear the driver continues to accelerate the vehicle, then begins to brake the vehicle.  
         [0077]    During vehicle braking the vehicle decelerates; the throttle angle is commanded to idle; the engine  200  speed is driven to idle; the vehicle remains in fourth gear; the halfshaft torque becomes negative; the motor  202  is operated as a generator and performs regenerative braking supplying negative torque to the drive wheels  204 ; the accelerator position is zero; the vehicle velocity error becomes negative; the clutch  210  disengages. As the vehicle decelerates the transmission down shifts. The vehicle comes to zero speed. The engine  200  remains at idle. Gear one is obtained. The halfshaft torque and motor  202  torque become zero, and the clutch  210  remains open. The driver commands acceleration at about 35 sec. The vehicle launches with motor  202  only until gear two. The previously described behavior continues.  
         [0078]    [0078]FIG. 13 shows that vehicle launch occurs in first gear using the traction motor  202 . During second gear, occurring at approximately seven seconds, the throttle angle increases from idle to about 70 degrees; the engine  200  speed ramps from idle to about 4000 rpm; the engine  200  torque increases from zero to 60 Nm; the motor  202  torque ramps from 50 Nm to zero; the driver accelerator command continues to increase; the vehicle continues to accelerate; the halfshaft torque follows the engine  200  torque; the vehicle velocity error goes to zero; the clutch  210  closes. Third gear operates as second gear. During the gear change from second to third the motor  202  torque rises to fill in during the gear shift.  
         [0079]    During fourth gear operation the driver stops commanding vehicle acceleration; the throttle angle decreases from 90 degrees to idle; the engine  200  speed decreases from about 3000 rpm to idle; the halfshaft torque shows a transition between positive torque to negative torque provided by regenerative braking; the engine  200  produces positive torque, transitions to negative brake torque, and then to idle torque; the motor  202  transitions from positive tractive torque to regenerative brake torque; the velocity error becomes negative; the clutch  210  does not fully engage, then disengages. When the engine  200  provides negative brake torque during the transition from positive torque to negative torque the clutch  210  is disengaged so that regenerative brake torque usage is optimized. During the beginning of fourth gear operation the driver is commanding over 80% throttle momentarily. During this time the motor  202 , after providing fill in torque during the gear shift from three to four, provides torque boost.  
         [0080]    The vehicle decelerates to a stop; the throttle angle remains at idle; the vehicle speed remains at idle; the gear changes from four to one even though the clutch  210  is disengaged such that the gear would be appropriate if the driver suddenly commanded acceleration; the halfshaft torque becomes zero, when regenerative brake torque can no longer be collected, leaving the hydraulic brakes to continue the task of vehicle deceleration alone; the engine  200  torque is zero the motor  202  torque goes to zero when regenerative braking is completed; the accelerator pedal  220  remains untouched by the driver; the vehicle velocity error goes to zero; the clutch  210  remains disengaged. The vehicle again accelerates upon driver request in a similar manner.  
         [0081]    Medium Acceleration/Deceleration Hybrid Operation.  
         [0082]    [0082]FIG. 14 shows simulation results of medium acceleration/deceleration hybrid operation. The operation in this profile is similar to the previous profile with the exception that more motor  202  boost occurs due to increased acceleration demand. The motor  202  boost operation can be noted in gears three and four. Additionally the vehicle gets into fifth gear.  
         [0083]    Repeated Wide Open Throttle Acceleration/Deceleration Hybrid Operation.  
         [0084]    During WOT operation, shown in FIG. 15 first gear behavior is as previously described. During second, third and fourth gears the driver is commanding full motor  202  and engine  200  torque; the vehicle is accelerating; full throttle is commanded and drops to idle during gear changes; halfshaft torque decreases with increasing gear due to motor  202  torque capability being limited as motor  202  speed increases and gear ratio decreases with increasing gear; vehicle velocity error remains approximately constant; the clutch  210  does not completely engage.  
         [0085]    During fifth gear the vehicle cruises and this is reflected in a reduced throttle angle. The engine  200  speed remains steady during cruising; the halfshaft torque remains steady during cruising; the engine  200  torque remains steady during cruising; the motor  202  torque remains zero during cruising; the driver command is small during cruising; the clutch  210  engages and remains engaged during cruising. The vehicle decelerates and the behavior is as previously described during deceleration. The acceleration and deceleration scenario is repeated.  
         [0086]    Engine  200  Only Simulation.  
         [0087]    The first engine  200  only simulation is with 60% accelerator pedal  220  depression shown in FIGS.  16 A-F. The vehicle accelerates in first gear; the throttle angle increases from idle to 80 degrees; the vehicle speed increases from idle to 3500 rpm; the halfshaft torque increases from zero to 800 Nm and reaches steady state of 400 Nm; the engine  200  torque increases from zero to 100 Nm. The clutch  210  disengages during gear changes; the engine  200  speed decreases; the halfshaft torque decreases; the engine  200  torque decreases. The remaining gears demonstrate similar behavior.  
         [0088]    Motor  202  Only Simulation.  
         [0089]    The simulation of motor  202  only shown in FIGS.  17 A-J demonstrates th vehile accelerating; the throttle angle at idle; the engine  200  speed at idle; the gears changing; smooth halfshaft torque; zero engine  200  torque; motor  202  torque increasing and decreasing with vehicle speed; accelerator pedal  220  command; small vehicle velocity error; a disengaged clutch  210 .  
         [0090]    Denouement for Torque Distribution of a Preferred Embodiment Post-Transmission PHEV.  
         [0091]    1. The PHEV coordinated controller provides motoring and regenerative commands to the motor controller  215  for corresponding positive and negative motor  202  torque, and throttle blade commands to the engine controller  217 . These commads may be based on th battery SOC, motor  202  speed versus torque limits, motor  202  torque current, motor  202  field current, transmission gear, driver pedal position, engine clutch  210  state, motor clutch  225  state, engine  200  speed, average power a the drive wheels  204 , shift status, estimated engine  200  torque, and estimated engine  200  torque available.  
         [0092]    2. The PHEV controller provides engine clutch  210  control during braking, or hybrid operation.  
         [0093]    3. The torque may be partitioned to operate in an engine  200  only mode, a motor  202  only mode, or a two traction device (hybrid) mode.  
         [0094]    4. Hybrid mode operation consists of motor  202  only operation, engine  200  operation, motor  202  torque application during shifting, motor  202  assist during power boost, and regenerative braking. During periods of low storage device operation, the engine  200  may be loaded with the alternator to increase the storage device operation.  
         [0095]    5. The vehicle launches in motor  202  only mode for optimal drivability, emissions, and fuel economy.  
         [0096]    6. A torque split algorithm determines the magnitudes of the motor  202  torque command and the engine  200  torque command.  
         [0097]    7. The torque split algorithm determines the accelerator pedal  220  command from the driver and determines the torque partitioning between the traction devices.  
         [0098]    8. The torque split algorithm for pre-transmission PHEV contains seventeen inputs:  
         [0099]    a. Motor 202 TQ Estimate in Nm  
         [0100]    b. brake 224 switch logic  
         [0101]    c. accelerator position in per unit values (0—no pedal command to 1—WOT)  
         [0102]    d. Maximum Engine  200  Torque Available at the Wheels  204  (TeMAXavailATwheels 204 ) in Nm  
         [0103]    e. accel pedal flag logic  
         [0104]    f. motor  202  only trigger logic  
         [0105]    g. Engine  200  Torque at the Wheels  204  (TeATwheels 204 ) in Nm  
         [0106]    h. engine  200  on c logic  
         [0107]    i. engine  200  on and shift b logic  
         [0108]    j. motor  202  assist no shift engine  200  on d logic  
         [0109]    k. gear ratio  
         [0110]    l. motor  202  only flag a logic  
         [0111]    m. motor  202  assist with shift flag e logic  
         [0112]    n. Maximum Motor  202  Torque Available at the Wheels  204  (TmATwheels 204 MAX) in Nm  
         [0113]    o. actual gear  
         [0114]    p. clutch  210  position logic  
         [0115]    q. clutch  210  state logic  
         [0116]    9. The torque split algorithm contains two outputs: (a) Te command at engine  200  in Nm; (b) torque command at motor  202  in Nm.  
         [0117]    10. When the vehicle is launched in motor  202  only mode, the amount of motor  202  torque commanded is a linear function based on the maximum motor  202  torque available at any instant and the percentage of accelerator pedal  220  depressed.  
         [0118]    11. This vehicle is capable of operating in a motor  202  only, engine  200  only or hybrid mode. Any mode that the driver chooses to operate the vehicle is transparent. The pedal interface between the driver and the vehicle is invisible to the driver.  
         [0119]    12. When the vehicle is operated in the hybrid mode and the vehicle transitions from motor  202  only mode to engine  200  on mode, the torque commanded by the driver at this transition is commanded initially to the motor  202 .  
         [0120]    13. When the vehicle transitions from motor  202  only to engine  200  on operation the motor  202  torque commanded must be saved at the exact accelerator pedal  220  position command from the driver during the transition.  
         [0121]    14. This saved motor  202  torque command and pedal position is used to scale that pedal position to 80% of pedal travel.  
         [0122]    15. The maximum engine  200  torque available at the wheels  204  corresponds to 80% accelerator pedal  220  travel.  
         [0123]    16. The difference between 80% of pedal travel and the saved percentage of pedal travel is used as a linear function with maximum engine  200  torque available, to command the engine  200  torque.  
         [0124]    17. The remaining 20% of pedal travel is used as a linear function with the maximum motor  202  torque available, to provide boost.  
         [0125]    18. At 80% accelerator pedal  220  travel no motor  202  torque is commanded, and at 100% accelerator pedal  220  travel the maximum motor  202  torque available is commanded.  
         [0126]    19. As the vehicle transitions from engine  200  operation to motor  202  only operation the engine  200  torque commanded at the transition and the accelerator pedal  220  position at the transition are saved.  
         [0127]    20. These saved values are used to linearly scale the motor  202  torque command.  
         [0128]    21. The motor  202  torque estimate is multiplied by gear ratios of transaxle and 4×4 to become the motor  202  torque at the wheels  204 .  
         [0129]    22. When the BRAKE SWITCH is high the accelerator position ACCEL POS is continuously being updated and the motor 202 perACCpedalSAVE is zero. When the BRAKE SWITCH goes low the ACCEL POS accelerator position is no longer updated and the present value is saved as motor 202 perACCpedalSAVE. Similarly, TmATwheels 204 SAVE is saved. When the BRAKE SWITCH is low then motor 202 perACCpedalSAVE is zero. When the BRAKE SWITCH goes high, then the accelerator position is saved as motor 202 perACCpedalSAVE and the motor  202  torque is saved as TmATwheels 204 SAVE.  
         [0130]    23. When the mtr only trigger is high the accelerator position ACCEL POS is continuously being updated and the TeperACCpedalSAVE is zero. When the mtr only trigger goes low the ACCEL POS accelerator position is no longer updated and the present value is saved as TeperACCpedalSAVE. Similarly, TeATwheels 204 SAVE is saved. When the mtr only trigger is low then TeperACCpedalSAVE is zero. When the mtr only trigger goes high, then the accelerator position is saved as TeperACCpedalSAVE and the engine  200  torque is saved as TeATwheels 204 SAVE.  
         [0131]    24. When not in motor  202  only trigger mode the engine  200  torque command is derived by subtracting the motor  202  accelerator percent pedal saved from the present accelerator pedal  220  value. This difference is the amount of extra pedal desired from the driver.  
         [0132]    25. The difference between the maximum engine  200  torque available at the wheels  204  and the motor  202  torque saved at the wheels  204  gives the engine  200  torque available for scaling.  
         [0133]    26. The difference between the 80% tip in value and the percent motor  202  accelerator pedal  220  saved determines the available percentage of the pedal for scaling.  
         [0134]    27. The engine  200  torque available multiplied with the amount of extra accelerator pedal  220  desired divided by the percent of accelerator pedal  220  scaled gives the engine  200  torque commanded referred to the wheels  204 .  
         [0135]    28. The absolute value of the engine  200  torque commanded at the wheels  204  is taken and multiplied by the sign of the amount of extra accelerator pedal  220  desired.  
         [0136]    29. The motor  202  torque saved at the wheels  204  is then added to the engine  200  torque command when the accelerator pedal  220  is depressed.  
         [0137]    30. When the amount of extra (torque) desired is negative, the accelerator position is less than the torque motor  202  per accelerator pedal  220  saved. When this occurs, the present accelerator position multiplied by the motor  202  torque saved at the wheels  204  divided by the percent motor  202  accelerator pedal  220  saved. This then is the engine  200  torque command else the previous engine  200  torque command is issued.  
         [0138]    31. When the motor  202  only trigger is high after being low the motor  202  torque command is the present accelerator position multiplied by the engine  200  torque at the wheels  204  saved divided by the engine  200  torque per accelerator pedal  220  saved.  
         [0139]    32. If the transmission is in neutral, then the engine  200  torque command is zero.  
         [0140]    33. The engine  200  torque command at the engine  200  becomes the engine  200  torque commanded at the wheels  204  divided by the gear ratio and the final drive.  
         [0141]    34. If a motor  202  assist non shifting mode is desired then the maximum engine  200  torque available at the wheels  204  is commanded. This occurs when the accelerator pedal  220  position is greater than 80%.  
         [0142]    35. The motor  202  torque commanded at the motor  202  is that motor  202  torque commanded at the wheels  204  divided by the 4×4 and transaxle gear ratios and filtered with a low pass filter.  
         [0143]    36. If the brake switch is high the torque command at the motor  202  is zero in this part of the algorithm.  
         [0144]    37. If the engine  200  clutch  210  is being commanded to engage and the clutch  210  is open and the transmission is in second gear then the motor  202  torque commanded at the wheels  204  is 30 Nm*4×4 and transaxle gear ratios. This is done in order to allow quicker engine  200  clutch  210  engagement to occur.  
         [0145]    38. If the motor  202  only flag, the motor  202  assist with shift flag or the engine  200  on and shift b flags are high then the motor  202  torque commanded at the wheels  204  is the acceleration position multiplied by the maximum motor  202  torque at the wheels  204 .  
         [0146]    39. Else if the motor  202  assist with no shift is high then the motor  202  torque commanded at the wheels  204  is the difference between the present acceleration position and 80% of the pedal travel multiplied by the maximum motor  202  torque available at the wheels  204  divided by 20% of the pedal travel.  
         [0147]    40. Else if the motor  202  only flag is high after previously being in a state where motor  202  only flag, or motor  202  assist with shift flag, or engine  200  on and shift flag, or motor  202  assist with no shift flag, was high then the motor  202  torque command at wheels  204  is the acceleration position multiplied by the engine  200  torque at the wheels  204  saved divided by the engine  200  torque percent accelerator pedal  220  saved. It is apparent to those skilled in the art that the present invention and method of utilization thereof can be readily utilized in vehicles having a pre-transmission parallel vehicle configuration or in vehicles where different drive axles are powered by the electric and IC engine  200 . In such vehicles, many of the parameters of the aforementioned are reduced or eliminated. However, the basic strategy of saving the torque demand on the electric motor  202  when transitioning to the IC engine  200  remains the same as well as the parameters in scaling the accelerator pedal  220 . Accordingly, other inputs to the aforementioned algorithm can be reduced or modified. However, the maximum engine  200  torque will be set at the 80% preferred value as previously described.  
         [0148]    It is apparent to those skilled in the art that the present invention and method of utilization thereof can be readily utilized in vehicles having a pre-transmission parallel vehicle configuration or in vehicles where different drive axles are powered by the electric and IC engine  200 . In such vehicles, many of the parameters of the forementioned are reduced or eliminated. However, the basis strategy of saving the torque demand on the electric motor  202  when transitioning to the IC engine  200  remains the same as well as the parameters in scaling the accelerator pedal  220 . Accordingly, other inputs to the aforementioned algorithm can be reduced or modified. However, the maximum engine  200  torque will be set at the 80% preferred value as previously described.