Abstract:
A powertrain includes a countershaft, a gearset including a sun gear, a carrier connected to an engine, a ring gear releasably held against rotation and connectable to the countershaft, and pinions supported on the carrier and meshing with the sun gear and ring gear, an electric machine connected to the sun gear and connectable to the countershaft, and a second electric machine driveably connected to the countershaft.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates generally to a powersplit powertrain for an extended range electric vehicle. 
     2. Description of the Prior Art 
     The powertrain of a hybrid electric vehicle (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. 
     An extended range electric vehicle (EREV) operates completely electrically while the battery charge is being depleted. 
     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 
     A powertrain includes a countershaft, a gearset including a sun gear, a carrier connected to an engine, a ring gear releasably held against rotation and connectable to the countershaft, and pinions supported on the carrier and meshing with the sun gear and ring gear, an electric machine connected to the sun gear and connectable to the countershaft, and a second electric machine driveably connected to the countershaft. 
     With this strategy, the motor and battery are not sized to drive entirely with electrical energy during the charge depleting mode. Instead, the engine is operated in high wheel torque pedal demand situations to keep components size, and thus cost, lower and to provide better value. 
     In a charge sustaining mode, the engine runs in either a series mode or a powersplit mode. 
     The powertrain provides full torque to the wheels from the traction motor, a benefit over a single mode powersplit powertrain. 
     The powertrain provides the high fuel economy and driveability of a powersplit powertrain with improved towing and vehicle launch capability. 
     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 
       The invention will be more readily understood by reference to the following description, taken with the accompanying drawings, in which: 
         FIG. 1  is a schematic diagram of a HEV powertrain; 
         FIG. 2  is lever diagram of the planetary gearset of the powertrain of  FIG. 1 ; 
         FIG. 3  is lever diagram of the gearset during an engine-off condition; 
         FIG. 4  is a schematic diagram of a PHEV powertrain; and 
         FIG. 5  is a chart showing the engaged and disengaged state of the clutches and brake for various operating modes of the powertrain of  FIG. 4 . 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring now to the drawings,  FIG. 1  illustrates a HEV powertrain  10  having a power flow architecture commonly known as powersplit. Powertrain  10  includes an engine  12 ; planetary gearset  14 ; electric machine  16 , driveably connected to the vehicle wheels through layshaft gearing  18 ; differential mechanism  20 ; and electric machine  22 . 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. 
     The planetary gearset  14  directs the engine power to either an electric drive path or a mechanical drive path. The sun gear  24  of the planetary gearset  14  is connected to the generator  22 . The carrier  25  of the planetary gearset  14  is connected to the engine  12  through a torsion damper  26  and shaft  27 . The ring gear  28  is connected to countershaft  34  and layshaft gear pair  36 - 37 . The rotor  30  of motor  16  is connected to countershaft  34  through the layshaft gear pair  32 - 33 . 
     Motor  16  is electrically connected to a traction battery  40  through an inverter  42  and a high voltage DC/DC converter  44 . Similarly generator  22  is electrically connected to battery  40  through an inverter  46  and converter  44 . 
     Countershaft  34  is connected through a pinion  50  and ring gear  52  of the differential mechanism  20 , which transmits power to the vehicle wheels through halfshafts or axle shafts  54 ,  56 . 
     An oil pump  58  is driveably connected to carrier  25  and the engine output by a pinion  60  and gear  62 . 
       FIG. 2  illustrates a lever diagram to visualize operation of planetary gearset  14  in a powersplit mode, wherein r represents the ring gear  28  connected to traction motor  16 , e represents the planet carrier  25  connected to engine  12 , g represents the sun gear  24  connected to generator  22 , ω represents angular velocity, and τ represents torque. 
       FIG. 3  shows a lever diagram for the engine off condition of powertrain  10 . When the speed of engine  12  is zero, generator  22  rotates in the opposite direction relative to the motor. In general, the generator&#39;s speed is about two to three times faster than the motor&#39;s speed. In the lever diagram of  FIG. 3 , ω r  is the speed of ring gear  28 , which is a function of vehicle speed; ω e  is the speed of engine  12 ; and ω g  is the speed of sun gear  24  and generator  22 =−β*ω r  wherein β=N r /N s  and N is the number of teeth of the respective gear. 
       FIG. 4  illustrates a powersplit powertrain  10 ′ for a PHEV. In  FIG. 4  similar components of the powertrain  10  of  FIG. 1  are identified by the same reference numbers. A first clutch  70  alternately opens and closes a drive connection between shaft  27  and ring gear  28 . A second clutch  72  alternately opens and closes a drive connection between generator  22  and a pinion  74 , which meshes with a gear  76 , secured to shaft  34 . A brake  78  alternately holds ring gear  28  against rotation and releases the ring gear.  FIG. 5  is a chart showing the engaged and disengaged state of the clutches  70 ,  72  and brake  78  for various operating modes of the powertrain  70 . 
     The clutches  70 ,  72  and brake  78  may be hydraulically-actuated friction disc control element, but are preferably control elements that do not have parasitic losses. 
       FIG. 5  is a chart showing the engaged and disengaged state of the clutches and brake for various operating modes of the powertrain of  FIG. 4 . 
     Mode 1: One Motor Electric Drive 
     When clutches  70 ,  72  and brake  78  are disengaged, motor  16  is isolated from the primary axis of shaft  27  and is connected directly to the wheels  80 ,  82  through layshaft gears  32 - 33 , countershaft  34 , layshaft gears  50 - 52 , differential  20 . Mode 1 is used to drive the vehicle electrically under most conditions. Losses are minimized due to the planetary gearset  14  and generator  22  not rotating. 
     Mode 2: Two Motor Electric Drive 
     When clutch  72  is engaged, and both clutch  70  and brake  78  are disengaged, generator  22  is connected to the countershaft  34  and drives the vehicle wheels  80 ,  82  through clutch  72 , layshaft gears  74 - 76 , countershaft  34 , layshaft gears  50 - 52 , and differential  20 . Mode 2 is used during electric drive (sometimes called charge depletion) to provide extra power and torque under conditions of high torque demand. Mode 2 allows the traction motor  16  to be downsized to reduce cost and to improve vehicle launch torque. 
     Mode 3: Series 
     When brake  78  is engaged and clutches  70 ,  72  are disengaged; generator  22  is driven through the planetary gearset  14  at about two to three times engine speed due to brake  78  grounding the ring gear  28  and providing a torque reaction. The traction motor  16  is connected directly to the wheels  80 ,  82  to provide propulsion. Mode 3, used during charge sustaining operation, is of particular benefit in reverse drive so that the reaction to engine torque is not provided by the traction motor  16 . Mode 3 allows full torque to the wheels from the traction motor  16 , which is a benefit over a single mode powersplit powertrain. 
     Mode 4: Powersplit 
     When clutch  70  is engaged, and both clutch  72  and brake  78  are disengaged, the planetary gearset  14  directs the engine power to either an electric drive path or a mechanical drive path. The sun gear  24  of the planetary gearset  14  is connected to the generator  22 . The carrier  25  of the planetary gearset  14  is connected to the engine  12  through a torsion damper  26  and shaft  27 . The ring gear  28  is connected to countershaft  34  through clutch  70  and layshaft gear pair  36 - 37 . The rotor  30  of motor  16  is connected to countershaft  34  through the layshaft gear pair  32 - 33 . 
     When the speed of engine  12  is zero, generator  22  rotates in the opposite direction relative to the engine  14 . Mode 4 is used in normal charge sustaining operation of the engine  12 , motor  16  and generator  22 . 
     Mode 5 and 6: Direct Drive 
     In mode 5, clutches  70 ,  72  are engaged and brake  78  is disengaged. In mode 6, clutch  72  and brake  78  are engaged and clutch  70  is disengaged. Engagement of clutch  72  connects countershaft  34  to sun gear  24  and generator  22 . 
     Modes 5 and 6 provide two modes wherein the engine  12  can be directly coupled to the wheels in a fixed gear ratio. In modes 5 and 6, both generator  22  and traction motor  16  can be turned off so that no traction power is transferred into the electrical domain. Depending on the selection of gear ratios, the gears provide improved efficiency within particular driving situations. The direct drive modes provide a benefit in that they produce less heat while towing a load. These modes improve the tow/payload capability of the powersplit powertrain  70 . 
     If the torque capacity of clutch  72  is sufficient to transmit vehicle launch torque, the engine  12  can be used to aid in the launch of the vehicle along with the two motors  16 ,  22 , so that under wheel high torque demand, full engine and battery power are used to drive the wheels during a launch condition. 
     Although the clutches  70 ,  72  and brake  78  have been describes as friction control elements, the clutches and brake may be lockable elements, such as dog clutch or brakes or lockable one-way clutches or brake. When the friction clutches and brake are used, they are actuated preferably by a hydraulic servo or an electrical ball/ramp. 
     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.