Abstract:
A method for controlling a hybrid electric vehicle powertrain includes operating an engine driveably connected to first vehicle wheels, providing an electric motor driveably connected to second vehicle wheels, shifting a gear selector between a forward drive position and a reverse drive position, reducing vehicle speed to or lower than a reference speed, and using a transmission located between the engine and the first wheels and the electric motor to produce reverse or forward drive corresponding to the position to which the gear selector is shifted.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    This invention relates generally to a powertrain for a hybrid electric vehicle (HEV), and more particularly, to controlling the actuators of a HEV when the driver requests a change from a forward to a reverse vehicle motion direction or from reverse to forward vehicle motion direction. 
         [0003]    2. Description of the Prior Art 
         [0004]    As illustrated in the  FIG. 1 , a HEV powertrain may be arranged with a first and second vehicle propulsion torque path. The first path may include an engine connected to an electric machine, such as a crank integrated starter-generator (CISG), and a multiple-speed, discrete ratio transmission connected to the electric machine, the first torque path being driveably connected to a first set of vehicle wheels. The second torque path includes an electric motor driveably connected to a second set of vehicle wheels, producing an electric rear axle drive (ERAD). 
         [0005]    The transmission may be a powershift transmission having dual input clutches and dual layshaft gear sets or an automatic transmission having planetary gear sets with a hydrokinetic torque converter and control elements for producing forward drive in multiple gear ratios and reverse drive. 
         [0006]    When a vehicle operator shifts a gear lever selector (i.e. PRNDL) between a forward drive position and a reverse drive position, or vice versa, the operator expects that the vehicle will slow down, stop, and then move in a direction opposite to the current direction of motion. To achieve this, in conventional vehicles, the transmission gear is disengaged from a forward gear and engaged into a reverse gear (or vice versa) if the vehicle speed is sufficiently low. But in a HEV powertrain which provides dual vehicle propulsion torque paths and is equipped with multiple torque actuators (i.e. engine, electric machines) and an automatic transmission, care has to be taken in switching from a forward to a reverse vehicle direction (or vice versa) in order to prevent unintended vehicle motion, engine stall, driveline disturbances, and potential damage to the powertrain actuators. 
         [0007]    A need exists in the industry for a powertrain control system technique that avoids these potential problems and provides the driver&#39;s expected vehicle function. 
       SUMMARY OF THE INVENTION 
       [0008]    A method for controlling a hybrid electric vehicle powertrain includes operating an engine driveably connected to first vehicle wheels, operating an electric motor driveably connected to second vehicle wheels, shifting a gear lever selector between a forward drive position and a reverse drive position, reducing vehicle speed to or lower than a reference speed, and using a transmission located between the engine and the first wheels to produce reverse or forward drive corresponding to the position to which the gear lever selector is shifted. 
         [0009]    The control method also uses the electric motor driveably connected to the second wheels and the transmission in order to change the vehicle motion direction in response to a change-of-mind shift of the gear lever selector, such as a forward to reverse (i.e. D-R) shift followed by a reverse to forward (i.e. R-D) shift, or the inverse of that shift. 
         [0010]    The control produces an appropriate change in gear range consistent with the driver&#39;s manual control of the gear lever selector. The control further prevents damage to the transmission, engine and electric motor, provides smooth gear engagement, and potentially alerts the driver to an inappropriate gear selection. 
         [0011]    The scope of applicability of the preferred embodiment will become apparent from the following detailed description, claims and drawings. It should be understood that the description and specific examples, although indicating preferred embodiments of the invention, are given by way of illustration only. Various changes and modifications to the described embodiments and examples will become apparent to those skilled in the art. 
     
    
     
       DESCRIPTION OF THE DRAWINGS 
         [0012]    The invention will be more readily understood by reference to the following description, taken with the accompanying drawings, in which: 
           [0013]      FIG. 1  is a schematic diagram of a schematic powertrain for a HEV; 
           [0014]      FIG. 2  is a schematic diagram showing details of a dual input clutch powershift transmission; and 
           [0015]      FIG. 3  is exemplary graph showing a function relating torque and vehicle speed. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0016]    As shown in  FIG. 1 , a vehicle powertrain and control system  12  includes an engine  14 , such as a diesel or gasoline engine; a transmission  16 , such as dual clutch powershift transmission or another multiple speed transmission; an electric machine  18 , such as a crank-integrated starter generator (CISG) driveably connected to the transmission input  20 ; and an additional electric machine  22 , such as an electric motor. Electric machine  18  provides starter/generator capability. 
         [0017]    Electric machine  22 , sometimes referred to as an electric rear axle drive unit (ERAD), is connected to the final drive of a rear axle  24  and provides additional propulsion capability in either an electric drive or hybrid (series/parallel) drive mode. In front-wheel drive (FWD) applications, electric machine  22  could also be connected to the final drive of a front axle at the output  26  of the transmission, and would be referred to as an electric front axle drive (EFAD) unit. Power output by the electric machine  22  drives vehicle wheels  28 ,  27  through ERAD gearing (not shown) and a final drive unit  30 , which is in the form of an inter-wheel differential mechanism. Similarly, the transmission output  26  is driveably (mechanically) connected to vehicle wheels  34 ,  35  through a final drive unit  36 , which includes an inter-wheel differential mechanism. 
         [0018]    Powertrain  12  can operate in major modes including: (1) series hybrid drive, in which engine  14  is running and producing combustion, transmission  16  is disengaged, CISG  18  is generating electric power, and ERAD  22  is alternately motoring and driving the vehicle wheels  28 , 27 ; (2) engine drive, in which CISG  18  and ERAD  22  are both inoperative and engine  14  is running with transmission  16  engaged in gear, as in a conventional powertrain; (3) parallel hybrid drive, in which engine  14  is running, transmission  16  is engaged in gear, CISG  18  and/or ERAD  22  are operative; (4) engine starting, in which CISG  18  is motoring to start the engine by driving the engine flywheel; and (5) engine stop, in which engine  14  is shut down. While operating in parallel hybrid drive mode, the powertrain can operate in several sub-modes including: (3.1) parallel hybrid drive  1 , in which CISG  18  is shutdown, ERAD  22  is motoring and generating; (3.2) parallel hybrid drive  2 , in which CISG  18  is motoring and ERAD  22  is shutdown; (3.3) parallel hybrid drive  3 , in which CISG  18  and ERAD  22  are motoring; and (3.4) parallel hybrid drive  4 , in which CISG  18  is generating and ERAD  22  is alternatively shutdown, motoring and generating. 
         [0019]    A vehicle controller  40  receives signals  42  representing the start or stopped status of an engine ignition key, signals  45  representing the manually selected position of a PRNDL gear lever selector  44 , signals  46  representing the magnitude of displacement from a reference position of an accelerator pedal  47 , signals  48  representing the magnitude of displacement from a reference position of a brake pedal  49 , signals  50  representing the angular displacement from a reference position of a steering wheel, signals  52  representing a desired vehicle speed selected through a vehicle speed control system, and signals  54  representing a selected air temperature and supply vent through which air is supplied to a passenger compartment through a climate control system. 
         [0020]    Controller  40  issues contactor open and close commands  56  for connecting an electric storage battery  58  to a high voltage bus  60 . Electric storage battery  58  is electrically connected to motor  22  and the starter generator  18  through the high voltage bus  60 . 
         [0021]    Controller  40  issues wheel brake torque commands  62  to a brake controller  64 , which actuates the wheel brakes  66 ,  68  with hydraulic brake pressure carried in lines  70 ,  72  to wheels  34 ,  35  to produce the commanded wheel brake torque represented by command signal  62 . The brakes, however, may be electrically actuated rather than hydraulically actuated. 
         [0022]    Controller  40  issues engine torque commands  74  to engine  14 , in response to which engine  14  produces on its crankshaft  76  the desired engine output torque represented by commands  74 . 
         [0023]    Controller  40  issues generator torque commands  78 , in response to which CISG  18  produces the desired torque at the transmission input  20  represented by commands  78 . 
         [0024]    Controller  40  issues motor torque commands  80 , in response to which motor  22  produces the desired motor torque on its shaft  82 . Controller  40  issues transmission gear commands  84 , in response to which transmission  16  produces the gear ratio of the desired gear represented by commands  84 . 
         [0025]    In a conventional multiple-speed automatic transmission  16 , forward gears and reverse drive are produced in accordance with engaged and disengaged states of friction control elements  86 ,  87 ,  88  enclosed in the transmission. The control elements  86 ,  87 ,  88 , which are clutches and brakes that alternately hold, interconnect and release components of planetary or layshaft gear sets, become engaged in response to hydraulic pressure and are released when pressure at the respective control element is vented. The states of the control elements combine to produce the forward and reverse gears produced by transmission  16 . 
         [0026]      FIG. 2  illustrates details of a dual input clutch, powershift transmission  240 , which includes a first input clutch  242  for selectively connecting the input  20  of the transmission alternately to the even-numbered forward gears and reverse gear associated with a first layshaft  244 , and a second input clutch  246 , for alternately connecting the input  20  to the odd-numbered gears associated with a second layshaft  249 . 
         [0027]    Layshaft  244  supports pinions  260 ,  262 ,  264 , which are each journalled on shaft  244 , and couplers  266 ,  268 , which are secured to shaft  244 . Pinions  260 ,  262 ,  264  are associated respectively with the second, fourth and sixth gears. Coupler  266  includes a sleeve  270 , which can be moved leftward to engage pinion  260  and driveably connect pinion  260  to shaft  244 . Coupler  268  includes a sleeve  272 , which can be moved leftward to engage pinion  262  and driveably connect pinion  262  to shaft  244  and can be moved rightward to engage pinion  264  and driveably connect pinion  264  to shaft  244 . 
         [0028]    Layshaft  249  supports pinions  274 ,  276 ,  278 , which are each journalled on shaft  249 , and couplers  280 ,  282 , which are secured to shaft  249 . Pinions  274 ,  276 ,  278  are associated respectively with the first, third and fifth gears. Coupler  280  includes a sleeve  284 , which can be moved leftward to engage pinion  274  and driveably connect pinion  274  to shaft  249 . Coupler  282  includes a sleeve  286 , which can be moved leftward to engage pinion  276  and driveably connect pinion  276  to shaft  249  and can be moved rightward to engage pinion  278  and driveably connect pinion  278  to shaft  249 . 
         [0029]    Transmission output  26  supports gears  288 ,  290 ,  292 , which are each secured to output shaft  26 . Gear  288  meshes with pinions  260  and  274 . Gear  290  meshes with pinions  262  and  276 . Gear  292  meshes with pinions  264  and  278 . 
         [0030]    A reverse pinion  296 , journalled on layshaft  244 , meshes with an idler  298 , which meshes with a reverse gear  300  secured to output shaft  26 . A coupler  302  selectively connects reverse pinion  296  to layshaft  244 . 
         [0031]    Couplers  266 ,  268 ,  280 ,  282  and  302  may be synchronizers, or dog clutches or a combination of these. 
         [0032]    The dual input clutch powershift automatic transmission  240  is prepared to produce the forward and reverse drive when the couplers connect the pinion associated with the desired gear to the appropriate layshaft  244 ,  249 . 
         [0033]    The control elements are the input clutches  242 ,  246 , whose engaged, disengaged and slipping states alternately connect and release input  20  and the respective layshafts  244 ,  249 . 
         [0034]    The method used by system  12  controls the four actuating subsystems, i.e., engine  14 , CISG  18 , transmission  16  and electric drive motor  22 , in various powertrain operating modes when the PRNDL gear lever selector  44  is shifted from drive to reverse or reverse to drive. 
         [0035]    In the electric drive operating mode during which motor  22  alone transmits power to the driven wheels  26 ,  27  and the driver shifts PRNDL gear selector  44  from drive to reverse or vice versa, engine  14  remains off, CISG  18  produces no output torque, transmission  16  is fully disengaged such that it transmits no torque to output  26 , and either: 
         [0036]    (i) motor  22  produces zero torque until the vehicle speed decreases to a reference vehicle speed, whereupon motor  22  produces output torque in axle  24  corresponding to the selected direction to which the gear lever selector  44  has been shifted; or 
         [0037]    (ii) motor  22  produces output torque in a direction corresponding to the selected direction to which the gear lever selector  44  has been shifted and at a magnitude defined by a torque-speed function  90 , such as that shown in  FIG. 3 . 
         [0038]    In the operating mode during which engine  14  alone produces power transmitted to the first wheels  34 ,  35 , and the driver shifts PRNDL gear selector  44  from drive to reverse or vice versa, motor  22  produces no output torque, and either: 
         [0039]    (i) transmission  16  is fully disengaged, i.e., transmits no torque to output  26 , until vehicle speed decreases to a reference speed, whereupon the transmission is fully engaged in a gear that corresponds to the reverse or forward selected direction to which the gear selector  44  has been shifted; or 
         [0040]    (ii) slip is produced across control elements  86 ,  87 ,  88  of transmission  16  or control elements  246 ,  242  of transmission  240  in the forward gear or reverse gear that corresponds to the selected position of the gear selector  44 , until vehicle speed decreases to a reference speed, whereupon the selected gear becomes fully engaged. 
         [0041]    In the series hybrid drive operating mode, in which engine  14  is running and producing combustion, CISG  18  is generating electric power, motor  22  is motoring, i.e., driving axle  24 , and the driver shifts PRNDL gear selector  44  from drive to reverse or vice versa, engine  14  remains running, and vehicle speed is reduced to a reference speed by either: 
         [0042]    (i) simulating engine braking by operating motor  22  in a generating mode producing torque in the reverse direction or forward drive direction in opposition to the rotational direction of wheels  28 ,  27 , and operate CISG  18  as a motor to rotate the engine in order to dissipate excess electric energy generated by motor  22 , which cannot be stored in the battery  58 ; or 
         [0043]    (ii) producing no output torque from motor  22 ; or 
         [0044]    (iii) producing output torque from motor  22  in a direction corresponding to the selected direction to which the gear selector  44  has been shifted and at a magnitude defined by a torque-speed function  90 . When vehicle speed has decreased to the reference speed, transmission  16  is fully engaged in the forward gear or reverse gear that corresponds to the reverse or forward selected direction to which the gear selector  44  has been shifted. 
         [0045]    In the parallel hybrid drive operating mode with engine  14  running, CISG  18  and ERAD  22  operative, when the driver shifts the PRNDL gear selector  44  from drive to reverse or vice versa, either: 
         [0046]    (i) disengage transmission  16  and produce zero output torque from motor  22  until vehicle speed decreases to a reference speed, then fully engage transmission  16  in the forward gear or reverse gear that corresponds to reverse or forward selected drive to which the gear selector  44  has been shifted; or 
         [0047]    (ii) disengage transmission  16  and operate motor  22  to produce output torque at wheels  28 ,  27  in a direction corresponding to the selected direction to which the gear selector  44  has been shifted and at a magnitude defined by a torque-speed function  90  until vehicle speed decreases to a reference speed, then fully engage transmission  16  in the forward gear or reverse gear that corresponds to the reverse or forward selected direction to which the gear selector  44  has been shifted; or 
         [0048]    (iii) if vehicle speed is lower than a reference speed, produce slip across the control elements of the transmission in the forward gear or reverse gear that corresponds to the selected position of the gear selector  44 , operate motor  22  to produce output torque in a direction corresponding to the selected direction to which the gear selector  44  has been shifted and at a magnitude defined by a torque-speed function  90  until vehicle speed decreases to a reference speed, then fully engage transmission  16  in the forward gear or reverse gear that corresponds to the reverse or forward selected direction to which the gear selector  44  has been shifted. 
         [0049]    In accordance with the provisions of the patent statutes, the preferred embodiment has been described. However, it should be noted that the alternate embodiments can be practiced otherwise than as specifically illustrated and described.