Abstract:
A method for controlling a powersplit transmission includes connecting an engine to the transmission, provided an engine torque request is present; connecting a motor to the transmission, provided an engine torque request is absent and the engine is on; and disconnecting the engine and motor from the transmission, provided the engine is off, and using a traction motor to produce wheel torque.

Description:
[0001]    This is a continuation-in-part application of pending U.S. application Ser. No. 13/198,062, filed Aug. 4, 2011. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    This invention relates generally to a powersplit powertrain for an electric vehicle, and particularly to operational control of a planetary gearset. 
         [0004]    2. Description of the Prior Art 
         [0005]    Fuel economy is critical in a hybrid electric vehicle (HEV). Spinning the planetary gears at all times consumes energy due to friction losses, which negatively affects fuel economy. 
         [0006]    The powertrain of a HEV includes an engine, electric motor/generator and traction battery, wherein the engine and motor can drive the wheels individually, the engine can charge the traction battery through the electric machine operating as a generator, and vehicle kinetic energy can be recovered and regenerated using the wheel brakes to drive the generator and recharge the battery. 
         [0007]    In the powertrain for a plug-in hybrid (PHEV), the traction battery is significantly increased in capacity so that electrical energy from the electric grid can be used to drive the vehicle. As a result, a much greater use of electric drive is expected. The direct connection of the generator to the wheel speed causes the generator shaft to rotate as the vehicle moves when the engine is off. This causes several issues including (i) as the vehicle increases in speed, the generator speed gets excessively high causing a durability concern for the bearing, planetary gearset and generator; (ii) lowering of available torque needed to start the engine; (iii) since the generator is not being used, it generates an unnecessary spin loss; and (iv) in reverse gear with the engine running, the motor must react, thereby reducing the torque provided to the wheels. 
       SUMMARY OF THE INVENTION 
       [0008]    A method for controlling a powersplit transmission includes connecting an engine to the transmission, provided an engine torque request is present; connecting a motor to the transmission, provided an engine torque request is absent and the engine is on; and disconnecting the engine and motor from the transmission, provided the engine is off, and using a traction motor to produce wheel torque. 
         [0009]    Conventional powersplit driveline spin the planetary gear set whenever the vehicle is moving or the engine is spinning. The control method configures hardware into a series hybrid configuration, but does not operate. The generator and engine do not turn until reconfigured into a Powersplit operating mode. Wheel torque and regeneration is handled by the traction motor during this operation. 
         [0010]    The control method disconnects the the planetary gear set to avoid losses and improve fuel economy, which is especially helpful when tip-out “sailing” is maximized. 
         [0011]    The powertrain provides full torque to the wheels from the traction motor, a benefit over a single mode powersplit powertrain. 
         [0012]    The powertrain provides the high fuel economy and driveability of a powersplit powertrain with improved towing and vehicle launch capability. 
         [0013]    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 
         [0014]    The invention will be more readily understood by reference to the following description, taken with the accompanying drawings, in which: 
           [0015]      FIG. 1  is a schematic diagram of a HEV powertrain; 
           [0016]      FIG. 2  is a chart showing the engaged and disengaged state of clutches that control the powertrain of  FIG. 1 . 
           [0017]      FIG. 3  is a schematic diagram of a HEV powertrain; 
           [0018]      FIG. 4  is a chart showing the engaged and disengaged state of clutches that control the powertrain of  FIG. 3 . 
           [0019]      FIG. 5  is a schematic diagram of a HEV powertrain; 
           [0020]      FIG. 6  is a chart showing the engaged and disengaged state of clutches that control the powertrain of  FIG. 5 . 
           [0021]      FIG. 7  is a schematic diagram of a HEV powertrain; 
           [0022]      FIG. 8  is a chart showing the engaged and disengaged state of clutches that control the powertrain of  FIG. 7 ; and 
           [0023]      FIG. 9  is a logic flow diagram of a control algorithm. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0024]    Referring first to  FIG. 1 , a powertrain  10  includes a power source such as an internal combustion engine  12 , such as a diesel engine or gasoline engine; a first planetary gearset  14 ; an electric motor  16 ; layshaft gearing  18 ; a differential mechanism  20 ; an electric generator  22 ; a countershaft  24 , which is driveably connected to differential mechanism  20 , output pinion  40  and motor  16 ; and a second planetary gearset  26 . Each electric machine  16 ,  22  is a motor-generator, although conventionally electric machine  16  is referred to as a motor or traction motor, and electric machine  22  is referred to as a generator. 
         [0025]    The sun gear  27  of the planetary gearset  14  is connected by clutch  28  to the generator  22 . The carrier  32  of the planetary gearset  14  is connected by clutch  30  to the engine  12  through a torsion damper  34  and shaft  36 . The ring gear  39  of gearset  14  is driveably connected to countershaft  24  by engaged output pinion  40  and gear  42 , which form a layshaft gear pair  40 - 42 . Planet pinions  43 , supported on carrier  32 , are in continual meshing engagement with ring gear  39  and sun gear  27 . 
         [0026]    The rotor  44  of motor  16  is connected to countershaft  24  through the gear pair  46 - 48 . 
         [0027]    Motor  16  is electrically connected to a traction battery  50  through an inverter  52  and a high voltage DC/DC converter  54 . Similarly, generator  22  is electrically connected to battery  50  through an inverter  56  and converter  54 . 
         [0028]    Countershaft  24  is connected through a pinion  60  and ring gear  62  of the differential mechanism  20 , which transmits power to the vehicle wheels  64 ,  66 , through halfshafts or axle shafts  68 ,  70 . 
         [0029]    An oil pump  72  is driveably connected to shaft  36  and the engine output by a pinion  74  and gear  76 . 
         [0030]    The sun gear  80  of planetary gearset  26  is connected by clutch  82  to the generator  22 . The carrier  86  of the planetary gearset  26  is connected by clutch  84  to the engine  12  through a torsion damper  34  and shaft  36 . The ring gear  88  of gearset  26  is fixed against rotation due to its connection to case  90 . Planet pinions  92 , supported on carrier  86 , are in continual meshing engagement with ring gear  88  and sun gear  80 . 
         [0031]    Powertrain  10  operates in powersplit mode when clutches  28 ,  30  are engaged and clutches  82 ,  84  are disengaged. Engine  12  is connected through clutch  30  to carrier  32 , and the rotor of generator  22  is connected through clutch  28  to sun gear  27 . In powersplit operation power produced by engine  12  and, if the battery  50  is supplying electric energy to generator, power produced by generator  26  is transmitted through gearset  14  and gear pair  40 - 42  to countershaft  24 , and power produced by motor  16  is transmitted by gear pair  46 - 48  to countershaft  24 . Final drive gear pair  60 - 62  transmits the power from engine  12 , motor  16  and generator  22  to differential mechanism  20 , which transmits power differentially to the vehicle wheels  64 ,  66 , through shafts  68 ,  70 . In powersplit operation with generator  22  operating as an electric generator, engine  12  supplies power to generator  22 , thereby allowing the battery  50  to be recharged. 
         [0032]    Powertrain  10  operates in series mode when clutches  28 ,  30  are disengaged and clutches  82 ,  84  engaged. Engine  12  is connected through clutch  84  to carrier  86  of gearset  26 , sun gear  80  is overdriven relative to the speed of engine  12 , and clutch  82  connects overdriven sun gear  80  to the rotor of generator  22 . In series operation power produced by engine  12  drives generator  26  at a relatively high speed, thereby recharging battery  50 , and power produced by motor  16  is transmitted by gear pair  46 - 48  to countershaft  24 . Final drive gear pair  60 - 62  transmits the power produced by motor  16  to differential mechanism  20 . 
         [0033]    In  FIG. 3 , clutch  84  is deleted, thereby directly, continually connecting carrier  86  of gearset  26  to engine  12  through shaft  36  and torsion damper  34 . The powertrain  94  of  FIG. 3  operates in powersplit mode when clutches  28 ,  30  are engaged and clutch  82  is disengaged. Engine  12  is connected through clutch  30  to carrier  32 , and the rotor of generator  22  is connected through clutch  28  to sun gear  27 . In powersplit operation, power produced by engine  12  and generator  26  is transmitted through gearset  14  and gear pair  40 - 42  to countershaft  24 , and power produced by motor  16  is transmitted by gear pair  46 - 48  to countershaft  24 . Final drive gear pair  60 - 62  transmits the power from engine  12 , motor  16  and generator  22  to differential mechanism  20 . In powersplit operation with generator  22  operating as an electric generator, engine  12  supplies power to generator  22 , thereby allowing the battery  50  to be recharged. 
         [0034]    The powertrain  94  of  FIG. 3  operates in series mode when clutches  28 ,  30  are disengaged and clutch  82  is engaged. Engine  12  is connected directly to carrier  86  of gearset  26 , sun gear  80  and the rotor of generator are overdriven relative to the speed of engine  12 , and clutch  82  connects overdriven sun gear  80  to the rotor of generator  22 . In series operation, power produced by engine  12  drives generator  26  at a relatively high speed, thereby recharging battery  50 , and power produced by motor  16  is transmitted by gear pair  46 - 48  to countershaft  24 . Final drive gear pair  60 - 62  transmits the power produced by motor  16  to differential mechanism  20 . 
         [0035]    In  FIG. 5 , clutch  84  is present, but clutch  82  is deleted, thereby directly, continually connecting sun gear  80  of gearset  26  to the rotor of generator  22 . The powertrain  96  of  FIG. 5  operates in powersplit mode when clutches  28 ,  30  are engaged and clutch  84  is disengaged. Engine  12  is connected through clutch  30  to carrier  32 , and the rotor of generator  22  is connected through clutch  28  to sun gear  27 . In powersplit operation, power produced by engine  12  and generator  26  is transmitted through gearset  14  and gear pair  40 - 42  to countershaft  24 , and power produced by motor  16  is transmitted by gear pair  46 - 48  to countershaft  24 . Final drive gear pair  60 - 62  transmits the power from engine  12 , motor  16  and generator  22  to differential mechanism  20 . In powersplit operation with generator  22  operating as an electric generator, engine  12  supplies power to generator  22 , thereby allowing the battery  50  to be recharged. 
         [0036]    The powertrain  96  of  FIG. 5  operates in series mode when clutches  28 ,  30  are disengaged and clutch  84  is engaged. Engine  12  is connected through clutch  84  to carrier  86  of gearset  26 , sun gear  80  is overdriven relative to the speed of engine  12  and connected directly to the rotor of generator  22 . In series operation, power produced by engine  12  drives generator  22  at a relatively high speed, thereby recharging battery  50 , and power produced by motor  16  is transmitted by gear pair  46 - 48  to countershaft  24 . Final drive gear pair  60 - 62  transmits the power produced by motor  16  to differential mechanism  20 . 
         [0037]    Powertrain  98  of  FIG. 7  includes a shaft  102 , connected to the rotor of generator  22 ; a pinion  100 , gear  104  meshing with pinion  102 ; a second countershaft  106  secure to gear  104  and to a pinion  108 ; a gear  110 , meshing with pinion  108 ; a clutch  112  for opening and closing a drive connection between shaft  36  and gear  110 ; a clutch  114  for opening and closing a drive connection between shaft  36  and carrier  32  of gearset  14 ; a clutch  116  for opening and closing a drive connection between sun gear  27  and shaft  102 ; and a clutch  118  for opening and closing a drive connection between shaft  102  and pinion  100 . 
         [0038]    Powertrain  98  operates in powersplit mode when clutches  114 ,  116  are engaged and clutches  112 ,  118  are disengaged. Engine  12  is connected through clutch  112  to carrier  32 , and the rotor of generator  22  is connected through clutch  116  to sun gear  27 . In powersplit operation, power produced by engine  12  and, if the battery  50  is supplying electric energy to generator, power produced by generator  26  is transmitted through gearset  14  and gear pair  40 - 42  to countershaft  24 , and power produced by motor  16  is transmitted by gear pair  46 - 48  to countershaft  24 . Final drive gear pair  60 - 62  transmits the power from engine  12 , motor  16  and generator  22  to differential mechanism  20 , which transmits power differentially to the vehicle wheels  64 ,  66 , through shafts  68 ,  70 . In powersplit operation with generator  22  operating as an electric generator, engine  12  supplies power to generator  22 , thereby allowing the battery  50  to be recharged. 
         [0039]    Powertrain  98  operates in series mode when clutches  112 ,  118  are engaged and clutches  114 ,  116  are disengaged. Engine  12  is connected through clutch  112 , gear  110 , pinion  108 , countershaft  106 , gear  104 , pinion  100  and shaft  102  to the rotor of generator  22 , which is overdriven relative to the speed of engine  12 . In series operation, power produced by engine  12  drives generator  26  at a relatively high speed, thereby recharging battery  50 , and power produced by motor  16  is transmitted by gear pair  46 - 48  to countershaft  24 . Final drive gear pair  60 - 62  transmits the power produced by motor  16  to differential mechanism  20 . 
         [0040]      FIG. 9  is a logic flow diagram representing a control algorithm for disengaging planetary gear set  14 , which disengagement avoids losses and improves fuel economy. At step  130  a test is performed to determine whether torque from engine  12  is requested. If the result of test  130  is logically negative, at step  132  a test is performed to determine whether engine  12  is shut off. 
         [0041]    If the result of test  130  is logically positive and the result of test  132  is negative, at step  134  C2 clutch  114  and C3 clutch  116  are closed, thereby spinning the planetary gear set  14  in the Powersplit mode, such that sun gear  27  is connected through C3 clutch  116  to generator  22  and pinion carrier  32  is connected through C2 clutch  114  to engine  12 . 
         [0042]    At step  136 , generator  22  and traction motor  16  are used with engine  12  to transmit torque to the driven wheels  64 ,  66 . Thereafter, control returns to step  130 . 
         [0043]    If the result of test  132  is positive, indicating that engine torque is not requested and engine  12  is shut off, at step  138  C2 clutch  114  and C3 clutch  116  are opened, thereby disconnecting sun gear  27  from generator  22  through C3 clutch  116  and disconnecting pinion carrier  32  from engine  12  through C2 clutch  114 . Thereafter, control returns to step  130 . 
         [0044]    At step  140 , only traction motor  16  is used to transmit torque to the driven wheels  64 ,  66  and for energy regeneration. 
         [0045]    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.