Abstract:
A powertrain includes an engine with an engine output member, such as a crankshaft, and a first motor/generator having a first rotor connected to the crankshaft for rotation therewith. A transmission includes a transmission input member, a transmission output member, and a differential gearing arrangement selectively operatively connecting the transmission input member and the transmission output member. A plurality of torque transmitting devices is selectively engageable to provide a plurality of fixed speed ratios between the transmission input member and the transmission output member. A second motor/generator includes a second rotor connected to the gearing arrangement to provide torque to the transmission output member. The transmission input member is selectively connectable to the engine output member and the first rotor to alternate between a series hybrid drive mode and a fixed ratio mode of powertrain operation. A corresponding method is also provided.

Description:
TECHNICAL FIELD 
     This invention relates to hybrid powertrains having an engine, a transmission, and two motor/generators, and characterized by a series hybrid mode and fixed ratio mode of operation. 
     BACKGROUND OF THE INVENTION 
     Electrically variable vehicle transmissions (EVTs), such as those described in U.S. Pat. No. 5,931,757, employ two electric motor/generators. The electric motor/generators are coaxially oriented with an input shaft connectable to an engine, an output shaft, and a plurality of planetary gearsets each having respective first, second, and third members. Each motor/generator is operatively connected to a respective member of one of the planetary gearsets to provide a range or mode of transmission operation characterized by a continuously variable speed ratio between the input shaft and the output shaft. The continuously variable speed ratio is proportional to the speed of one of the motor/generators. 
     In light vehicles using gasoline or hydrogen engines, electrical friction losses in EVT motor windings, iron, and controllers may become more significant than in heavy-duty vehicles. These engines may not be as sensitive to speed for emissions, so some of the advantages of an electrically variable transmission may not be as significant in very light vehicles compared to heavy-duty vehicles. 
     SUMMARY OF THE INVENTION 
     A vehicle powertrain is provided that includes an engine having an engine output member such as a crankshaft. A first motor/generator has a first rotor that is connected to the engine output member for unitary rotation. A transmission includes a transmission input member, a transmission output member, and a geartrain having a plurality of gear members. A plurality of torque transmitting devices are operatively connected to the gear members and are selectively engageable to provide a plurality of fixed speed ratios between the transmission input member and the transmission output member. A second motor/generator includes a second rotor operatively connected to one of the plurality of gear members for unitary rotation. 
     The connection of the first rotor to the engine output member enables a series hybrid mode of powertrain operation wherein there is no mechanical connection between the engine output member and the transmission output member, such as during vehicle launch. In the series hybrid mode, electrical energy is supplied to the second motor/generator from an energy storage device and/or from the first motor generator as it is driven by the engine output member. The engine output member and the first rotor are selectively connectable to the transmission input member to provide a fixed-ratio mode of powertrain operation with a mechanical connection between the engine output member and the transmission output member. 
     The fixed-ratio mode of operation enables power transmission from the engine to the transmission output member without engagement of the motor/generators, thereby eliminating or minimizing electrical losses. Furthermore, the first motor/generator may be significantly smaller than the motor/generators typically used in other electrically variable transmissions. The direct connection of the first motor/generator to the engine output member enables the first motor/generator to start the engine. 
     The first motor/generator may be used for engine inertial energy absorption whereby the first motor/generator absorbs power from the engine during shifts between fixed speed ratios. The first motor/generator converts mechanical energy from the engine to electrical energy, which is then stored in an energy storage device and later used to power the electric motor/generators. The engine inertial energy absorption enables a reduction in clutch size and clutch wear. Reduced clutch size results in reduced spin losses in the transmission. 
     The above features and advantages and other features and advantages of the present invention are readily apparent from the following detailed description of the best modes for carrying out the invention when taken in connection with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic representation of a powertrain embodying the concepts of the present invention; 
         FIG. 2  is a fixed ratio truth table for the transmission of the powertrain depicted in  FIG. 1 ; 
         FIG. 3  is a schematic representation of an alternative powertrain configuration embodying the concepts of the present invention; 
         FIG. 4  is a fixed-ratio truth table for the transmission of the powertrain depicted in  FIG. 3 ; 
         FIG. 5  is a schematic representation of another alternative powertrain configuration embodying the concepts of the present invention; and 
         FIG. 6  is a fixed-ratio truth table for the transmission of the powertrain depicted in  FIG. 5 . 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to  FIG. 1 , a vehicle powertrain  10  is schematically depicted. The powertrain  10  includes an engine  11  and a transmission  12 . The transmission  12  includes first, second, and third planetary gearsets  14 ,  16 ,  18 , each having respective first, second, and third members. More specifically, the first planetary gearset  14  includes a sun gear member  20 , a ring gear member  22 , and a planet carrier assembly  24 . The first planetary gearset  14  is compound, and thus planet carrier assembly  24  rotatably supports a first set of planet gears  26 A that mesh with sun gear member  20 . The planet carrier assembly  24  also rotatably supports a second set of planet gears  26 B that mesh with the first set of planet gears  26 A and with ring gear member  22 . 
     The second planetary gearset  16  includes a sun gear member  28 , ring gear member  22 , and a planet carrier assembly  30 . It should be noted that the ring gear member  22  is common to both the first and second planetary gearsets  14 ,  16 . Accordingly, the ring gear of the first planetary gearset  14  and the ring gear of the second planetary gearset  16  are connected for unitary rotation. The planet carrier assembly  30  rotatably supports planet gears  32  that meshingly engage ring gear member  22  and sun gear member  28 . Planet carrier assembly  24  is operatively connected to planet carrier assembly  30  for unitary rotation therewith. Alternatively, and within the scope of the claimed invention, planetary gearsets  14 ,  16  may share a common carrier assembly that rotatably supports planet gears  26 A,  26 B, and  32 . 
     The third planetary gearset  18  includes sun gear member  34 , ring gear member  36 , and planet carrier assembly  38 . The planet carrier assembly  38  rotatably supports planet gears  40  that meshingly engage ring gear member  36  and sun gear member  34 . It should be noted that, where used in the claims, first, second, and third members of planetary gearsets do not necessarily refer to a member of a particular type; thus, for example, a first member may be any one of a ring gear member, sun gear member, or planet carrier assembly. Similarly, as used in the claims, the respective first, second, or third members of two or more gearsets may or may not be the same type of member. 
     The powertrain  10  also includes a first electric motor/generator  42  and a second electric motor/generator  46 . An electrical storage device, such as battery  48 , is provided for supplying current to motor/generators  42 ,  46  when they operate in a motoring mode, and receiving charging current from motor/generators  42 ,  46  when they operate in a generating mode. An electronic control unit (ECU)  50 , including a microprocessor-based controller and suitable inverter circuitry, couples the battery  48  to motor/generators  42 ,  46 , and controls the same in response to various input signals, including the driver torque request signal (not shown) and the output shaft speed signal (not shown). In a preferred embodiment, the motor/generators  42 ,  46  are configured as induction machines, although other configurations are also possible. The first electric motor/generator  42  includes a stator  52  rigidly affixed to a stationary member such as transmission housing  54 . The first electric motor/generator  42  also includes a rotor  56 . The rotor  56  is continuously connected to the crankshaft  58  of the engine  11  for substantially unitary rotation therewith. 
     The second electric motor/generator  46  includes a stator  60  that is affixed to the housing  54 , and a rotor  62 . The rotor  62  is connected to sun gear member  34  and sun gear member  20  for unitary rotation therewith via an interconnecting member, such as sleeve  64 . 
     Planet carrier assembly  24  is operatively connected to main shaft  66  for rotation therewith. Planet carrier assembly  38  is operatively connected to an output member such as output shaft  68  for rotation therewith. An input member, such as input shaft  70 , is connected to the ring gear member  22  for rotation therewith. Input shaft  70 , output shaft  68 , sleeve  64 , and shaft  66  are rotatable about a common axis. The motor/generators  42 ,  46  and planetary gearsets  14 ,  16 ,  18  are coaxially aligned about the common axis. 
     The transmission  12  further includes a plurality of selectively engageable torque transmitting devices, or clutches, C 1 -C 6 . More particularly, clutch C 1  is a brake configured to selectively couple ring gear member  36  to the housing  54 . Clutch C 2  selectively couples shaft  66  and the planet carrier assemblies  24 ,  30  of the first and second planetary gearsets  14 ,  16  to the planet carrier assembly  38  of the third planetary gearset  18 , and, accordingly, to the output shaft  68 , for unitary rotation. Clutch C 3  is a brake configured to selectively couple sleeve  64 , and therefore the rotor  62  of the second electric motor/generator  46 , the sun gear member  20  of the first planetary gearset  14 , and the sun gear member  34  of the third planetary gearset  18 , to the housing  54 . Clutch C 4  is configured to selectively couple ring gear member  22  and sun gear member  28  for unitary rotation. Clutch C 5  is selectively engageable to connect the rotor  56  and the crankshaft  58  to the input member  70  of the transmission  12  for substantially unitary rotation therewith. The input member  70  may be directly driven by the crankshaft  58  and rotor  56 , or a transient torque damper (not shown) may be incorporated between the rotor  56  and the input member  70 . An example of a transient torque damper of the type recommended for the present usage is disclosed in detail in U.S. Pat. No. 5,009,221,issued Apr. 23, 1991 to Spitler, and which is hereby incorporated by reference in its entirety. Clutch C 6  is a brake configured to selectively couple sun gear member  28  to the housing  54 . 
     The ECU  50  is configured to control the engagement of the torque transmitting devices C 1 -C 6  via hydraulic actuation in a manner understood by those skilled in the art. Referring to  FIGS. 1 and 2 , the ECU  50  is programmed to provide a series mode of operation during vehicle launch, i.e., when the vehicle in which powertrain  10  is installed is at rest. In the series mode of operation, clutch C 1  is engaged, clutches C 2 -C 6  are disengaged, and motor/generator  46  supplies torque to the output shaft  68  via the third planetary gearset  18 . The electric power to drive motor/generator  46  may be provided from the battery  48 , from motor/generator  42  (driven by the engine  11 ), or a combination of both the battery and motor/generator  42 . The series mode of operation is characterized by the absence of a mechanical connection between the engine  11  and the output shaft  68 . It should be noted that ratios associated with a series mode of operation in the figures refer to the ratio between the second motor/generator  46  and the output member  68 . 
     Subsequent to the series mode of operation, the ECU  50  is programmed to cause the engagement of clutch C 5 , at a time determined by inputs such as torque demand and output shaft speed, to connect the input shaft  70 , and accordingly, ring gear member  22 , to the rotor  56  and the crankshaft  58 . The ECU  50  then controls the speed of the engine  11  so that clutch C 4  speed synchronizes; clutch C 4  is then applied to mechanically connect the engine  11  to the output shaft  68  through a first fixed speed ratio. First motor generator  42 , second motor/generator  46 , or both may provide torque to increase total power output to the wheels of the vehicle. 
     The transmission  12  is characterized by six fixed ratios. A second fixed speed ratio is achieved when clutches C 1 , C 6 , and CS are engaged and clutches C 2 -C 4  are disengaged. A third fixed speed ratio is achieved when clutches C 1 , C 2 , and CS are engaged and clutches C 3 , C 4 , and C 6  are disengaged. A fourth fixed ratio is achieved when clutches C 2 , C 6 , and CS are engaged, and clutches C 1 , C 3 , and C 4  are disengaged. A fifth fixed ratio is achieved when clutches C 2 , C 4 , and CS are engaged, and clutches C 1 , C 3 , and C 6  are disengaged. A sixth fixed speed ratio is achieved when clutches C 2 , C 3 , and C 5  are engaged, and when clutches C 1 , C 4 , and C 6  are disengaged. Shifting from the first fixed speed ratio through the sixth fixed speed ratio is asynchronous. 
     The ECU  50  may cause the first motor/generator  42  to operate as a generator during shifts to convert shift inertial energy to electrical energy which is stored in battery  48 . The energy can then be released from the battery after the shift. More specifically, during the time when an offgoing clutch has lost capacity and before an oncoming clutch has gained capacity, motor/generator  42  can convert power from the engine  11  to electrical energy instead of allowing the power to dissipate as heat in the clutches. 
     Further, motor/generator  42  provides a direct means of starting the engine  11  via crankshaft  58  to reduce vibration issues. 
     Referring to  FIG. 3 , wherein like reference numbers refer to like components from  FIG. 1 , powertrain  110  includes an alternative transmission  112  configuration. The transmission  112  includes first, second, and third planetary gearsets  114 ,  116 ,  118 , each having respective first, second, and third members. More specifically, the first planetary gearset  114  includes a sun gear member  120 , a ring gear member  122 , and a planet carrier assembly  124 . Planet carrier assembly  124  rotatably supports a set of planet gears  126  that mesh with sun gear member  120  and with ring gear member  122 . 
     The second planetary gearset  116  includes a sun gear member  128 , ring gear member  129 , and a planet carrier assembly  130 . The planet carrier assembly  130  rotatably supports planet gears  132  that meshingly engage ring gear member  129  and sun gear member  128 . 
     The third planetary gearset  118  includes sun gear member  134 , ring gear member  136 , and planet carrier assembly  138 . The planet carrier assembly rotatably supports planet gears  140  that meshingly engage ring gear member  136  and sun gear member  134 . 
     The transmission  112  also includes a first electric motor/generator  42  and a second electric motor/generator  46 . An electrical storage device, such as the battery shown at  48  in  FIG. 1 , is provided for supplying current to motor/generators  42 ,  46  when operating in a motoring mode, and receiving charging current from motor/generators  42 ,  46  when operating in a generating mode. An electronic control unit (not shown in  FIG. 3 ) couples the battery to motor/generators  42 ,  46 , and controls the same in response to various input signals, including the driver torque request signal (not shown) and the output shaft speed signal (not shown). The first electric motor/generator  42  includes a stator  52  rigidly affixed to a stationary member such as transmission housing  54 . The first electric motor/generator  42  also includes a rotor  56 . The rotor  56  is connected to the crankshaft  58  of the engine  11  for rotation therewith. 
     The second electric motor/generator  46  includes a stator  60  that is affixed to the housing  54 , and a rotor  62 . The rotor  62  is connected to sun gear member  134  and sun gear member  128  via an interconnecting member, such as sleeve  164 , for unitary rotation therewith. 
     Planet carrier assembly  124  and planet carrier assembly  130  are operatively connected to main shaft  166  for rotation therewith. Sun gear members  128 ,  134  and rotor  62  are operatively connected to sleeve  164  for rotation therewith. Sun gear member  120  is operatively connected to ring gear member  129  for rotation therewith. Planet carrier assembly  138  is operatively connected to an output member such as output shaft  68  for rotation therewith. An input member, such as input shaft  70 , is connected to the ring gear member  122  for rotation therewith. 
     The transmission  112  further includes a plurality of selectively engageable torque transmitting devices or clutches C 1 -C 6 . More particularly, clutch C 1  is a brake configured to selectively couple ring gear member  136  to the housing  54 . Clutch C 2  selectively couples shaft  166 , the planet carrier assembly  124  of the first planetary gearset  114 , and the planet carrier  130  of the second planetary gearset  116  to the planet carrier assembly  138  of the third planetary gearset, and, accordingly, to the output shaft  68 , for unitary rotation. Clutch C 3  is a brake configured to selectively couple sleeve  164 , and therefore the rotor  62  of the second electric motor/generator  46 , the sun gear member  128  of the second planetary gearset  114 , and the sun gear member  134  of the third planetary gearset  118 , to the housing  54 . Clutch C 4  is configured to selectively couple ring gear member  129  and sun gear member  120  to sleeve  164  for unitary rotation. Clutch C 5  is selectively engageable to connect the rotor  56  and the crankshaft  58  to the input member  70  of the transmission  112  for substantially unitary rotation therewith. Clutch C 6  is a brake configured to selectively couple sun gear member  120  and ring gear member  129  to the housing  54 . 
     Referring to  FIGS. 3 and 4 , the ECU is programmed to provide a series mode of operation wherein clutch Cl is engaged, clutches C 2 -C 6  are disengaged, and motor/generator  46  supplies torque to the output shaft  68  via the third planetary gearset  118 . The electric power to drive motor/generator  46  may be provided from the battery, from motor/generator  42  (driven by the engine  11 ), or a combination of both the battery and motor/generator  42 . 
     The ECU is programmed to cause the engagement of clutch C 5  at a predetermined time, based on inputs such as torque demand and output shaft speed, to connect the input shaft  70 , and accordingly, ring gear member  122 , to the rotor  56  and the crankshaft. The ECU then controls the speed of the engine  11  so that clutch C 4  speed synchronizes; clutch C 4  is then applied to mechanically connect the engine  11  to the output shaft  68  through a first fixed speed ratio. First motor generator  42 , second motor/generator  46 , or both may provide torque to increase total power output to the wheels of the vehicle. 
     The transmission  112  is characterized by six fixed ratios. A second fixed speed ratio is achieved when clutches C 1 , C 6 , and C 5  are engaged and clutches C 2 -C 4  are disengaged. A third fixed speed ratio is achieved when clutches C 1 , C 2 , and C 5  are engaged and clutches C 3 , C 4 , and C 6  are disengaged. A fourth fixed ratio is achieved when clutches C 2 , C 6 , and C 5  are engaged, and clutches C 1 , C 3 , and C 4  are disengaged. A fifth fixed ratio is achieved when clutches C 2 , C 4 , and C 5  are engaged, and clutches C 1 , C 3 , and C 6  are disengaged. A sixth fixed speed ratio is achieved when clutches C 2 , C 3 , and C 5  are engaged, and when clutches C 1 , C 4 , and C 6  are disengaged. Shifting from the first fixed speed ratio through the sixth fixed speed ratio is asynchronous. 
     Referring to  FIG. 5 , powertrain  210  is similar the powertrain of  FIG. 1 , except clutch C 4  interconnects different gear members. More specifically, first planetary gearset  214  includes sun gear member  220 , ring gear member  222 , and planet carrier assembly  224 . The first planetary gearset  214  is compound, and thus planet carrier assembly  224  rotatably supports a first set of planet gears  226 A that meshingly engage sun gear member  220 . The planet carrier assembly  224  also rotatably supports a second set of planet gears  226 B that meshingly engage the first set of planet gears  226 A and ring gear member  222 . 
     Second planetary gearset  216  includes sun gear member  228 , ring gear member  222 , and planet carrier assembly  230 . The planet carrier assembly  230  rotatably supports planet gears  232  that meshingly engage ring gear member  222  and sun gear member  228 . Planet carrier assembly  224  is operatively connected to planet carrier assembly  230  for unitary rotation therewith. 
     Third planetary gearset  218  includes sun gear member  234 , ring gear member  236 , and planet carrier assembly  238 . The planet carrier assembly  238  rotatably supports planet gears  240  that meshingly engage ring gear member  236  and sun gear member  234 . 
     The powertrain  210  also includes first electric motor/generator  42  and second electric motor/generator  46 . An electrical storage device, such as battery  48 , is provided for supplying current to motor/generators  42 ,  46  when they operate in a motoring mode, and receiving charging current from motor/generators  42 ,  46  when they operate in a generating mode. ECU  50  couples the battery  48  to motor/generators  42 ,  46 , and controls the same in response to various input signals, including the driver torque request signal (not shown) and the output shaft speed signal (not shown). 
     The first electric motor/generator  42  includes a stator  52  rigidly affixed to a stationary member such as transmission housing  54 . The first electric motor/generator  42  also includes a rotor  56 . The rotor  56  is connected to the crankshaft  58  of the engine  11  for rotation therewith. The second electric motor/generator  46  includes a stator  60  that is affixed to the housing  54 , and a rotor  62 . The rotor  62  is connected to sun gear member  234  and sun gear member  220  for unitary rotation therewith via an interconnecting member, such as sleeve  264 . 
     Planet carrier assembly  224  is operatively connected to main shaft  266  for rotation therewith. Planet carrier assembly  238  is operatively connected to an output member such as output shaft  68  for rotation therewith. An input member  270 , is connected to the ring gear member  222  for rotation therewith. Input member  270 , output shaft  68 , sleeve  264 , and shaft  266  are rotatable about a common axis. The motor/generators  42 ,  46  and planetary gearsets  214 ,  216 ,  218  are coaxially aligned about the common axis. 
     The transmission  212  further includes a plurality of selectively engageable torque transmitting devices or clutches C 1 -C 6 . More particularly, clutch C 1  is a brake configured to selectively couple ring gear member  236  to the housing  54 . Clutch C 2  selectively couples shaft  266  and planet carrier assembly  224  to the planet carrier assembly  238  of the third planetary gearset, and, accordingly, to the output shaft  68 , for unitary rotation. Clutch C 3  is a brake configured to selectively couple sleeve  264 , and therefore the rotor  62  of the second electric motor/generator  46 , the sun gear member  220  of the first planetary gearset  214 , and the sun gear member  234  of the third planetary gearset  218 , to the housing  54 . Clutch C 4  is configured to selectively couple sun gear member  228  with the sleeve  264 , and accordingly to rotor  62 , sun gear member  220 , and sun gear member  234 , for unitary rotation. Clutch C 5  is selectively engageable to connect the rotor  56  and the crankshaft  58  to the input member  270  of the transmission  212  for substantially unitary rotation therewith. Clutch C 6  is a brake configured to selectively couple sun gear member  228  to the housing  54 . 
     ECU  50  is configured to control the engagement of the torque transmitting devices C 1 -C 6  via hydraulic actuation in a manner understood by those skilled in the art. Referring to  FIGS. 5 and 6 , ECU  50  is programmed to provide a series mode of operation during vehicle launch and a fixed ratio mode of operation subsequent to the series mode. The clutch engagement for the series mode and the fixed ratio modes are the same for the powertrain  210  of  FIG. 5  and for the powertrain  10  of  FIG. 1 . 
     While the best modes for carrying out the invention have been described in detail, those familiar with the art to which this invention relates will recognize various alternative designs and embodiments for practicing the invention within the scope of the appended claims.