Abstract:
The electrically variable transmission family provides low-content, low-cost electrically variable transmission mechanisms including first, second and third differential gear sets, a battery, three electric machines serving interchangeably as motors or generators and at least one brake operable to enable series hybrid reverse operation. The three motor/generators are operable in a coordinated fashion to yield an EVT with a continuously variable range of speeds (including reverse).

Description:
TECHNICAL FIELD 
     The present invention relates to electrically variable transmissions having three planetary gear sets, three motor/generators and at least one brake that are controllable to provide continuously variable speed ratio ranges. 
     BACKGROUND OF THE INVENTION 
     Electric hybrid vehicles offer the potential for significant fuel economy improvements over their conventional counterparts; however, their market penetration is limited because of their relatively high cost/benefit ratio. It becomes pertinent to develop hybrid technologies that reduce cost and improve vehicle fuel economy. Two of the contributors to the cost of the hybrid vehicle are the energy storage (battery) power capacity and the size of the electric motor/generators required to realize all-electric reverse in many electric-variable-transmission (EVT)-based hybrid systems. One of the factors that affect the efficiency of the system is the operating efficiency of the motor/generators. 
     SUMMARY OF THE INVENTION 
     This invention describes continuously-variable hybrid transmissions that utilize a combination of three interconnected planetary gear sets, electric motor/generators and brakes to offer multi-mode EVTs with capability for series hybrid reverse driving, thus reducing the need for massive and expensive energy storage (battery), and to minimize operating the motor/generators under highly inefficient conditions. In the series hybrid reverse driving mode, power from the engine is used to drive at least one of the motor/generators to generate electric power, and the generated electric power is delivered to at least one of the other motor/generators to drive the vehicle in the forward or reverse direction. This capability eliminates the need for significant power from the battery to drive the vehicle in reverse. 
     The continuously-variable hybrid transmission family of the present invention provides low-content, low-cost electrically variable transmission mechanisms including first, second and third differential gear sets, a battery (or similar energy storage device), three electric machines serving interchangeably as motors or generators and at least one brake. Preferably, the differential gear sets are planetary gear sets, but other gear arrangements may be implemented, such as bevel gears or differential gearing to an offset axis. 
     In this description, the first, second and third planetary gear sets may be counted first to third in any order (i.e., left to right, right to left, etc.). 
     Each of the three planetary gear sets has three members. The first, second or third member of each planetary gear set can be any one of a sun gear, ring gear or carrier, or alternatively a pinion. 
     Each carrier can be either a single-pinion carrier (simple) or a double-pinion carrier (compound). 
     The input shaft is continuously connected with a member of the planetary gear sets. The output shaft is continuously connected with another member of the planetary gear sets. 
     A first interconnecting member continuously connects the first member of the first planetary gear set with the first member of the second planetary gear set. 
     A second interconnecting member continuously connects the second member of the first planetary gear set with the first member of the third planetary gear set. 
     A third interconnecting member continuously connects the second member of the second planetary gear set with the second member of the third planetary gear set. 
     A first motor/generator is connected to a member of the first or second planetary gear set. 
     A second motor/generator is connected to a member of the second or third planetary gear set. 
     A third motor/generator is connected to another member of the first or third planetary gear set. 
     The motor/generators are connected with the members of the planetary gear sets either directly or through other planetary gear sets, belt/chain or off-set gears with or without torque multiplication. 
     A first brake selectively connects a member of the first, second or third planetary gear set with a stationary member (transmission housing/casing). This brake is operable to hold the member stationary and enable series hybrid mode operation. Using the first brake rather than one of the motor/generators to enable the hybrid mode of operation reduces the torque capacity requirement for the motors and improves efficiency. Also, application of the first brake during electric-only drive (forward or reverse) allows the engine to be started without “engine start shock”. 
     Optionally, an additional brake or brakes, i.e., a second or third brake, selectively connects another member of the planetary gear sets with a stationary member and is operable to selectively hold this member of the planetary gear sets stationary under certain operating conditions to provide different EVT ranges, 
     The brakes may further be connected in parallel with one or more of the motor/generators and be selectively applied under operating conditions that would otherwise require one of the motor/generators to operate at zero or near-zero speeds, thereby improving efficiency by preventing the inefficient use of electric power to maintain zero or near-zero speed. This may further reduce the torque capacity (size) requirement of the motor/generators. 
     The brakes arc preferably electromechanically actuated to eliminate the need for the high-pressure hydraulic pump and associated losses; however, other conventional brake actuation methods may be used. 
     The three motor/generators are operated in a coordinated fashion to yield continuously variable forward and reverse speed ratios between the input shaft and the output shaft, while minimizing the rotational speeds of the motor-generators and optimizing the overall efficiency of the system. The tooth ratios of the planetary gear sets can be suitably selected to match specific applications. 
     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 including an electrically variable transmission incorporating a family member of the present invention; 
         FIG. 2  is a schematic representation of a powertrain including an electrically variable transmission incorporating another family member of the present invention; 
         FIG. 3  is a schematic representation of a powertrain including an electrically variable transmission incorporating another family member of the present invention; 
         FIG. 4  is a schematic representation of a powertrain including an 
       electrically variable transmission incorporating another family member of the present invention; 
         FIG. 5  is a schematic representation of a powertrain including an electrically variable transmission incorporating another family member of the present invention; 
         FIG. 6  is a schematic representation of a powertrain including an electrically variable transmission incorporating another family member of the present invention; 
         FIG. 7  is a schematic representation of a powertrain including an 
       electrically variable transmission incorporating another family member of the present invention; 
         FIG. 8  is a schematic representation of a powertrain including an electrically variable transmission incorporating another family member of the present invention; and 
         FIG. 9  is a schematic representation of a powertrain including an electrically variable transmission incorporating another family member of the present invention. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     With reference to  FIG. 1 , a powertrain  10  is shown, including an engine  12  connected to one preferred embodiment of the improved electrically variable transmission (EVT), designated generally by the numeral  14 . Transmission  14  is designed to receive at least a portion of its driving power from the engine  12 . As shown, the engine  12  has an output shaft that serves as the input member  17  of the transmission  14 . A transient torque damper (not shown) may also be implemented between the engine  12  and the input member  17  of the transmission. 
     In the embodiment depicted the engine  12  may be a fossil fuel engine, such as a gasoline or diesel engine which is readily adapted to provide its available power output typically delivered at a selectable number of revolutions per minute (RPM). 
     Irrespective of the means by which the engine  12  is connected to the transmission input member  17 , the transmission input member  17  is operatively connected to a planetary gear set in the transmission  14 . 
     An output member  19  of the transmission  14  is connected to a final drive  16 . 
     The transmission  14  utilizes three differential gear sets, preferably in the nature of planetary gear sets  20 ,  30  and  40 . The planetary gear set  20  employs an outer gear member  24 , typically designated as the ring gear. The ring gear member  24  circumscribes an inner gear member  22 , typically designated as the sun gear. A carrier member  26  rotatably supports a plurality of planet gears  27  such that each planet gear  27  simultaneously, and meshingly engages both the outer, ring gear member  24  and the inner, sun gear member  22  of the first planetary gear set  20 . 
     The planetary gear set  30  also employs an outer gear member  34 , typically designated as the ring gear. The ring gear member  34  circumscribes an inner gear member  32 , typically designated as the sun gear. A carrier member  36  rotatably supports a plurality of planet gears  37  such that each planet gear  37  simultaneously, and meshingly engages both the outer, ring gear member  34  and the inner, sun gear member  32  of the planetary gear set  30 . 
     The planetary gear set  40  also employs an outer gear member  44 , typically designated as the ring gear. The ring gear member  44  circumscribes an inner gear member  42 , typically designated as the sun gear. A carrier member  46  rotatably supports a plurality of planet gears  47  such that each planet gear  47  simultaneously, and meshingly engages both the outer, ring gear member  44  and the inner, sun gear member  42  of the planetary gear set  40 . 
     The input shaft  17  is continuously connected to the carrier member  26  of the planetary gear set  20 . The output shaft  19  is continuously connected to the carrier member  46  of the planetary gear set  40 . 
     A first interconnecting member  70  continuously connects the carrier member  26  of the planetary gear set  20  with the ring gear member  34  of the planetary gear set  30 . A second interconnecting member  72  continuously connects the ring gear member  24  of the planetary gear set  20  with the ring gear member  44  of the planetary gear set  40 . A third interconnecting member  74  continuously connects the carrier member  36  of the planetary gear set  30  with the sun gear member  42  of the planetary gear set  40 . 
     A brake  50  selectively connects the ring gear member  24  of the planetary gear set  20  and the ring gear member  44  of the planetary gear set  40  via the interconnecting member  72  with the transmission housing  60 . This brake  50  enables series hybrid driving mode wherein power from the engine  12  is used to drive motor/generator  80  to generate electric power, and the generated electric power is delivered to at least one of the other motor/generators  82 ,  84  to drive the vehicle in forward or reverse. 
     The first embodiment  10  also incorporates first, second and third motor/generators  80 ,  82  and  84 , respectively. The stator of the first motor/generator  80  is secured to the transmission housing  60 . The rotor of the first motor/generator  80  is secured to the sun gear member  22  of the planetary gear set  20 . 
     The stator of the second motor/generator  82  is secured to the transmission housing  60 . The rotor of the second motor/generator  82  is secured to the sun gear member  42  of the planetary gear set  40 . 
     The stator of the third motor/generator  84  is secured to the transmission housing  60 . The rotor of the third motor/generator  84  is secured to the sun gear member  32  of the planetary gear set  30 . 
     Returning now to the description of the power sources, it should be apparent from the foregoing description, and with particular reference to  FIG. 1 , that the transmission  14  selectively receives power from the engine  12 . The hybrid transmission also receives power from an electric power source  86 , which is operably connected to a controller  88 . The electric power source  86  may be one or more batteries. Other electric power sources, such as capacitors or fuel cells, that have the ability to provide, or store, and dispense electric power may be used in place of or in combination with batteries without altering the concepts of the present invention. The speed ratio between the input shaft and output shaft is prescribed by the speeds of the three motor/generators and the ring gear/sun gear tooth ratios of the planetary gear sets. Those with ordinary skill in the transmission art will recognize that desired input/output speed ratios can be realized by suitable selection of the speeds of the three motor/generators. 
     DESCRIPTION OF A SECOND EXEMPLARY EMBODIMENT 
     With reference to  FIG. 2 , a powertrain  110  is shown, including an engine  12  connected to another embodiment of the improved electrically variable transmission (EVT), designated generally by the numeral  114 . Transmission  114  is designed to receive at least a portion of its driving power from the engine  12 . As shown, the engine  12  has an output shaft that serves as the input member  17  of the transmission  114 . A transient torque damper (not shown) may also be implemented between the engine  12  and the input member  17  of the transmission. 
     In the embodiment depicted the engine  12  may be a fossil fuel engine, such as a gasoline or diesel engine which is readily adapted to provide its available power output typically delivered at a selectable number of revolutions per minute (RPM). 
     Irrespective of the means by which the engine  12  is connected to the transmission input member  17 , the transmission input member  17  is operatively connected to a planetary gear set in the transmission  114 . 
     An output member  19  of the transmission  114  is connected to a final drive  16 . 
     The transmission  114  utilizes three differential gear sets, preferably in the nature of planetary gear sets  120 ,  130  and  140 . The planetary gear set  120  employs an outer gear member  124 , typically designated as the ring gear. The ring gear member  124  circumscribes an inner gear member  122 , typically designated as the sun gear A carrier member  126  rotatably supports a plurality of planet gears  127  such that each planet gear  127  simultaneously, and meshingly engages both the outer, ring gear member  124  and the inner, sun gear member  122  of the first planetary gear set  120 . 
     The planetary gear set  130  also employs an outer gear member  134 , typically designated as the ring gear. The ring gear member  134  circumscribes an inner gear member  132 , typically designated as the sun gear. A carrier member  136  rotatably supports a plurality of planet gears  137  such that each planet gear  137  simultaneously, and meshingly engages both the outer, ring gear member  134  and the inner, sun gear member  132  of the planetary gear set  130 . 
     The planetary gear set  140  also employs an outer gear member  144 , typically designated as the ring gear. The ring gear member  144  circumscribes an inner gear member  142 , typically designated as the sun gear. A carrier member  146  rotatably supports a plurality of planet gears  147  such that each planet gear  147  simultaneously, and meshingly engages both the outer, ring gear member  144  and the inner, sun gear member  142  of the planetary gear set  140 . 
     The input shaft  17  is continuously connected to the ring gear member  124  of the planetary gear set  120 . The output shaft  19  is continuously connected to the carrier member  146  of the planetary gear set  140 . 
     A first interconnecting member  170  continuously connects the ring gear member  124  of the planetary gear set  120  with the ring gear member  134  of the planetary gear set  130 . A second interconnecting member  172  continuously connects the carrier member  126  of the planetary gear set  120  with the ring gear member  144  of the planetary gear set  140 . A third interconnecting member  174  continuously connects the carrier member  136  of the planetary gear set  130  with the sun gear member  142  of the planetary gear set  140 . 
     A brake  150  selectively connects the carrier member  126  of the planetary gear set  120  and the ring gear member  144  of the planetary gear set  140  via interconnecting member  172  with the transmission housing  160 . This brake  150  enables series hybrid mode operation in forward and reverse. 
     The second embodiment  110  also incorporates first, second and third motor/generators  180 ,  182  and  184 , respectively. The stator of the first motor/generator  180  is secured to the transmission housing  160 . The rotor of the first motor/generator  180  is secured to the sun gear member  122  of the planetary gear set  120 . 
     The stator of the second motor/generator  182  is secured to the transmission housing  160 . The rotor of the second motor/generator  182  is secured to the sun gear member  142  of the planetary gear set  140 . 
     The stator of the third motor/generator  184  is secured to the transmission housing  160 . The rotor of the third motor/generator  184  is secured to the sun gear member  132  of the planetary gear set  130 . 
     The hybrid transmission  114  receives power from the engine  12 , and also exchanges power with an electric power source  186 , which is operably connected to a controller  188 . 
     DESCRIPTION OF A THIRD EXEMPLARY EMBODIMENT 
     With reference to  FIG. 3 , a powertrain  210  is shown, including an engine  12  connected to another embodiment of the improved electrically variable transmission (EVT), designated generally by the numeral  214 . Transmission  214  is designed to receive at least a portion of its driving power from the engine  12 . As shown, the engine  12  has an output shaft that serves as the input member  17  of the transmission  214 . A transient torque damper (not shown) may also be implemented between the engine  12  and the input member  17  of the transmission. 
     In the embodiment depicted the engine  12  may be a fossil fuel engine, such as a gasoline or diesel engine which is readily adapted to provide its available power output typically delivered at a selectable number of revolutions per minute (RPM). 
     Irrespective of the means by which the engine  12  is connected to the transmission input member  17 , the transmission input member  17  is operatively connected to a planetary gear set in the transmission  214 . 
     An output member  19  of the transmission  214  is connected to a final drive  16 . 
     The transmission  214  utilizes three differential gear sets, preferably in the nature of planetary gear sets  220 ,  230  and  240 . The planetary gear set  220  employs an outer gear member  224 , typically designated as the ring gear The ring gear member  224  circumscribes an inner gear member  222 , typically designated as the sun gear. A carrier member  226  rotatably supports a plurality of planet gears  227  such that each planet gear  227  simultaneously, and meshingly engages both the outer, ring gear member  224  and the inner, sun gear member  222  of the first planetary gear set  220 . 
     The planetary gear set  230  also employs an outer gear member  234 , typically designated as the ring gear. The ring gear member  234  circumscribes an inner gear member  232 , typically designated as the sun gear. A carrier member  236  rotatably supports a plurality of planet gears  237  such that each planet gear  237  simultaneously, and meshingly engages both the outer, ring gear member  234  and the inner, sun gear member  232  of the planetary gear set  230 . 
     The planetary gear set  240  also employs an outer gear member  244 , typically designated as the ring gear. The ring gear member  244  circumscribes an inner gear member  242 , typically designated as the sun gear. A carrier member  246  rotatably supports a plurality of planet gears  247  such that each planet gear  247  simultaneously, and meshingly engages both the outer, ring gear member  244  and the inner, sun gear member  242  of the planetary gear set  240 . 
     The input shaft  17  is continuously connected to the carrier member  226  of the planetary gear set  220 . The output shaft  19  is continuously connected to the carrier member  246  of the planetary gear set  240 . 
     A first interconnecting member  270  continuously connects the carrier member  226  with the carrier member  236 . A second interconnecting member  272  continuously connects the ring gear member  224  with the ring gear member  244 . A third interconnecting member  274  continuously connects the ring gear member  234  with the sun gear member  242 . 
     A brake  250  selectively connects the ring gear member  224  and the ring gear member  244  via interconnecting member  272  with the transmission housing  260 . This brake  250  enables series hybrid mode operation in forward and reverse. 
     The embodiment  210  also incorporates first, second and third motor/generators  280 ,  282  and  284 , respectively. The stator of the first motor/generator  280  is secured to the transmission housing  260 . The rotor of the first motor/generator  280  is secured to the sun gear member  222  of the planetary gear set  220 . 
     The stator of the second motor/generator  282  is secured to the transmission housing  260 . The rotor of the second motor/generator  282  is secured to the sun gear member  242  of the planetary gear set  240 . 
     The stator of the third motor/generator  284  is secured to the transmission housing  260 . The rotor of the third motor/generator  284  is secured to the sun gear member  232  of the planetary gear set  230 . 
     The hybrid transmission  214  receives power from the engine  12 , and also exchanges power with an electric power source  286 , which is operably connected to a controller  288 . 
     DESCRIPTION OF A FOURTH EXEMPLARY EMBODIMENT 
     With reference to  FIG. 4 , a powertrain  310  is shown, including an engine  12  connected to another embodiment of the improved electrically variable transmission (EVT), designated generally by the numeral  314 . Transmission  314  is designed to receive at least a portion of its driving power from the engine  12 . As shown, the engine  12  has an output shaft that serves as the input member  17  of the transmission  314 . A transient torque damper (not shown) may also be implemented between the engine  12  and the input member  17  of the transmission. 
     In the embodiment depicted the engine  12  may be a fossil fuel engine, such as a gasoline or diesel engine which is readily adapted to provide its available power output typically delivered at a selectable number of revolutions per minute (RPM). 
     Irrespective of the means by which the engine  12  is connected to the transmission input member  17 , the transmission input member  17  is operatively connected to a planetary gear set in the transmission  14 . An output member  19  of the transmission  314  is connected to a final drive  16 . 
     The transmission  314  utilizes three differential gear sets, preferably in the nature of planetary gear sets  320 ,  330  and  340 . The planetary gear set  320  employs an outer gear member  324 , typically designated as the ring gear. The ring gear member  324  circumscribes an inner gear member  322 , typically designated as the sun gear. A carrier member  326  rotatably supports a plurality of planet gears  327  such that each planet gear  327  simultaneously, and meshingly engages both the outer, ring gear member  324  and the inner, sun gear member  322  of the first planetary gear set  320 . 
     The planetary gear set  330  also employs an outer gear member  334 , typically designated as the ring gear. The ring gear member  334  circumscribes an inner gear member  332 , typically designated as the sun gear. A carrier member  336  rotatably supports a plurality of planet gears  337  such that each planet gear  337  simultaneously, and meshingly engages both the outer, ring gear member  334  and the inner, sun gear member  332  of the planetary gear set  330 . 
     The planetary gear set  340  also employs an outer gear member  344 , typically designated as the ring gear. The ring gear member  344  circumscribes an inner gear member  342 , typically designated as the sun gear. A carrier member  346  rotatably supports a plurality of planet gears  347  such that, each planet gear  347  simultaneously, and meshingly engages both the outer, ring gear member  344  and the inner, sun gear member  342  of the planetary gear set  340 . 
     The input shaft  17  is continuously connected to the ring gear member  324  of the planetary gear set  320 . The output shaft  19  is continuously connected to the carrier member  346  of the planetary gear set  340 . 
     A first interconnecting member  370  continuously connects the ring gear member  324  with the carrier member  336 . A second interconnecting member  372  continuously connects the carrier member  326  with the ring gear member  344 . A third interconnecting member  374  continuously connects the ring gear member  334  with the sun gear member  342 . 
     A brake  350  selectively connects the carrier member  326  and the ring gear member  344  via interconnecting member  372  with the transmission housing  360 . This brake  350  enables series hybrid mode operation in forward and reverse. 
     The embodiment  310  also incorporates first, second and third motor/generators  380 ,  382  and  384 , respectively. The stator of the first motor/generator  380  is secured to the transmission housing  360 . The rotor of the first motor/generator  380  is secured to the sun gear member  322 . 
     The stator of the second motor/generator  382  is secured to the transmission housing  360 . The rotor of the second motor/generator  382  is secured to the sun gear member  342 . 
     The stator of the third motor/generator  384  is secured to the transmission housing  360 . The rotor of the third motor/generator  384  is secured to the sun gear member  332 . 
     The hybrid transmission  314  receives power from the engine  12 , and also exchanges power with an electric power source  386 , which is operably connected to a controller  388 . 
     DESCRIPTION OF A FIFTH EXEMPLARY EMBODIMENT 
     With reference to  FIG. 5 , a powertrain  410  is shown, including an engine  12  connected to another embodiment of the improved electrically variable transmission (EVT), designated generally by the numeral  414 . Transmission  414  is designed to receive at least a portion of its driving power from the engine  12 . As shown, the engine  12  has an output shaft that serves as the input member  17  of the transmission  414 . A transient torque damper (not shown) may also be implemented between the engine  12  and the input member  17  of the transmission. 
     In the embodiment depicted the engine  12  may be a fossil fuel engine, such as a gasoline or diesel engine which is readily adapted to provide its available power output typically delivered at a selectable number of revolutions per minute (RPM). 
     Irrespective of the means by which the engine  12  is connected to the transmission input member  17 , the transmission input member  17  is operatively connected to a planetary gear set in the transmission  414 . An output member  19  of the transmission  414  is connected to a final drive  16 . 
     The transmission  414  utilizes three differential gear sets, preferably in the nature of planetary gear sets  420 ,  430  and  440 . The planetary gear set  420  employs an outer gear member  424 , typically designated as the ring gear. The ring gear member  424  circumscribes an inner gear member  422 , typically designated as the sun gear. A carrier member  426  rotatably supports a plurality of planet gears  427  such that each planet gear  427  simultaneously, and meshingly engages both the outer, ring gear member  424  and the inner, sun gear member  422  of the first planetary gear set  420 . 
     The planetary gear set  430  also employs an outer gear member  434 , typically designated as the ring gear. The ring gear member  434  circumscribes an inner gear member  432 , typically designated as the sun gear. A carrier member  436  rotatably supports a plurality of planet gears  437  such that each planet gear  437  simultaneously, and meshingly engages both the outer, ring gear member  434  and the inner, sun gear member  432  of the planetary gear set  430 . 
     The planetary gear set  440  also employs an outer gear member  444 , typically designated as the ring gear. The ring gear member  444  circumscribes an inner gear member  442 , typically designated as the sun gear. A carrier member  446  rotatably supports a plurality of planet gears  447  such that, each planet gear  447  simultaneously, and meshingly engages both the outer, ring gear member  444  and the inner, sun gear member  442  of the planetary gear set  440 . 
     The input shaft  17  is continuously connected to the carrier member  426 . The output shaft  19  is continuously connected to the ring gear member  444 . 
     A first interconnecting member  470  continuously connects the carrier member  426  with the carrier member  436 . A second interconnecting member  472  continuously connects the ring gear member  424  with the carrier member  446 . A third interconnecting member  474  continuously connects the ring gear member  434  with the sun gear member  442 . 
     A first brake  450  selectively connects the ring gear member  424  and the carrier member  446  via interconnecting member  472  with the transmission housing  460 . This brake  450  enables series hybrid mode operation in forward and reverse. A second brake  452  selectively connects the sun gear member  442  with the transmission housing  460 . 
     The embodiment  410  also incorporates first, second and third motor/generators  480 ,  482  and  484 , respectively. The stator of the first motor/generator  480  is secured to the transmission housing  460 . The rotor of the first motor/generator  480  is secured to the sun gear member  422 . 
     The stator of the second motor/generator  482  is secured to the transmission housing  460 . The rotor of the second motor/generator  482  is secured to the sun gear member  442 . 
     The stator of the third motor/generator  484  is secured to the transmission housing  460 . The rotor of the third motor/generator  484  is secured to the sun gear member  432 . 
     The hybrid transmission  414  receives power from the engine  12 , and also exchanges power with an electric power source  486 , which is operably connected to a controller  488 . 
     DESCRIPTION OF A SIXTH EXEMPLARY EMBODIMENT 
     With reference to  FIG. 6 , a powertrain  510  is shown, including an engine  12  connected to another embodiment of the improved electrically variable transmission (EVT), designated generally by the numeral  514 . Transmission  514  is designed to receive at least a portion of its driving power from the engine  12 . As shown, the engine  12  has an output shaft that serves as the input member  17  of the transmission  514 . A transient torque damper (not shown) may also be implemented between the engine  12  and the input member  17  of the transmission. 
     In the embodiment depicted the engine  12  may be a fossil fuel engine, such as a gasoline or diesel engine which is readily adapted to provide its available power output typically delivered at a selectable number of revolutions per minute (RPM). 
     Irrespective of the means by which the engine  12  is connected to the transmission input member  17 , the transmission input member  17  is operatively connected to a planetary gear set in the transmission  514 . An output member  19  of the transmission  514  is connected to a final drive  16 . 
     The transmission  514  utilizes three differential gear sets, preferably in the nature of planetary gear sets  520 ,  530  and  540 . The planetary gear set  520  employs an outer gear member  524 , typically designated as the ring gear. The ring gear member  524  circumscribes an inner gear member  522 , typically designated as the sun gear. A carrier member  526  rotatably supports a plurality of planet gears  527  such that each planet gear  527  simultaneously, and meshingly engages both the outer, ring gear member  524  and the inner, sun gear member  522  of the planetary gear set  520 . 
     The planetary gear set  530  also employs an outer gear member  534 , typically designated as the ring gear. The ring gear member  534  circumscribes an inner gear member  532 , typically designated as the sun gear. A carrier member  536  rotatably supports a plurality of planet gears  537  such that each planet gear  537  simultaneously, and meshingly engages both the outer, ring gear member  534  and the inner, sun gear member  532  of the planetary gear set  530 . 
     The planetary gear set  540  also employs an outer gear member  544 , typically designated as the ring gear. The ring gear member  544  circumscribes an inner gear member  542 , typically designated as the sun gear. A carrier member  546  rotatably supports a plurality of planet gears  547  such that, each planet gear  547  simultaneously, and meshingly engages both the outer, ring gear member  544  and the inner, sun gear member  542  of the planetary gear set  540 . 
     The input shaft  17  is continuously connected to the sun gear member  522 . The output shaft  19  is continuously connected to the carrier member  546 . 
     A first interconnecting member  570  continuously connects the carrier member  526  with the ring gear member  534 . A second interconnecting member  572  continuously connects the ring gear member  524  with the ring gear member  544 . A third interconnecting member  574  continuously connects the carrier member  536  with the carrier member  546 . 
     A brake  550  selectively connects the ring gear member  524  and the ring gear member  544  via interconnecting member  572  with the transmission housing  560 . This brake  550  enables series hybrid mode operation in forward and reverse. 
     The embodiment  510  also incorporates first, second and third motor/generators  580 ,  582  and  584 , respectively. The stator of the first motor/generator  580  is secured to the transmission housing  560 . The rotor of the first motor/generator  580  is secured to the carrier member  526 . 
     The stator of the second motor/generator  582  is secured to the transmission housing  560 . The rotor of the second motor/generator  582  is secured to the sun gear member  542 . 
     The stator of the third motor/generator  584  is secured to the transmission housing  560 . The rotor of the third motor/generator  584  is secured to the sun gear member  532 . 
     The hybrid transmission  514  receives power from the engine  12 , and also exchanges power with an electric power source  586 , which is operably connected to a controller  588 . 
     DESCRIPTION OF A SEVENTH EXEMPLARY EMBODIMENT 
     With reference to  FIG. 7 , a powertrain  610  is shown, including an engine  12  connected to another embodiment of the improved electrically variable transmission (EVT), designated generally by the numeral  614 . Transmission  614  is designed to receive at least a portion of its driving power from the engine  12 . As shown, the engine  12  has an output shaft that serves as the input member  17  of the transmission  614 . A transient torque damper (not shown) may also be implemented between the engine  12  and the input member  17  of the transmission. 
     In the embodiment depicted the engine  12  may be a fossil fuel engine, such as a gasoline or diesel engine which is readily adapted to provide its available power output typically delivered at a selectable number of revolutions per minute (RPM). 
     Irrespective of the means by which the engine  12  is connected to the transmission input member  17 , the transmission input member  17  is operatively connected to a planetary gear set in the transmission  614 . An output member  19  of the transmission  614  is connected to a final drive  16 . 
     The transmission  614  utilizes three differential gear sets, preferably in the nature of planetary gear sets  620 ,  630  and  640 . The planetary gear set  620  employs an outer gear member  624 , typically designated as the ring gear. The ring gear member  624  circumscribes an inner gear member  622 , typically designated as the sun gear. A carrier member  626  rotatably supports a plurality of planet gears  627  such that each planet gear  627  simultaneously, and meshingly engages both the outer, ring gear member  624  and the inner, sun gear member  622  of the first planetary gear set  620 . 
     The planetary gear set  630  also employs an outer gear member  634 , typically designated as the ring gear. The ring gear member  634  circumscribes an inner gear member  632 , typically designated as the sun gear. A carrier member  636  rotatably supports a plurality of planet gears  637  such that each planet gear  637  simultaneously, and meshingly engages both the outer, ring gear member  634  and the inner, sun gear member  632  of the planetary gear set  630 . 
     The planetary gear set  640  also employs an outer gear member  644 , typically designated as the ring gear. The ring gear member  644  circumscribes an inner gear member  642 , typically designated as the sun gear. A carrier member  646  rotatably supports a plurality of planet gears  647  such that each planet gear  647  simultaneously, and meshingly engages both the outer, ring gear member  644  and the inner, sun gear member  642  of the planetary gear set  640 . 
     The input shaft  17  is continuously connected to the carrier member  626 . The output shaft  19  is continuously connected to the ring gear member  644 . 
     A first interconnecting member  670  continuously connects the carrier member  626  with the ring gear member  634 . A second interconnecting member  672  continuously connects the ring gear member  624  with the carrier member  646 . A third interconnecting member  674  continuously connects the carrier member  636  with the sun gear member  642 . 
     A first brake  650  selectively connects the ring gear member  624  and the carrier member  646  via interconnecting member  672  with the transmission housing  660 . This brake  650  enables series hybrid mode operation in forward and reverse. A second brake  652  selectively connects the sun gear member  642  with the transmission housing  660 . 
     The embodiment  610  also incorporates first, second and third motor/generators  680 ,  682  and  684 , respectively. The stator of the first motor/generator  680  is secured to the transmission housing  660 . The rotor of the first motor/generator  680  is secured to the sun gear member  622 . 
     The stator of the second motor/generator  682  is secured to the 
     transmission housing  660 . The rotor of the second motor/generator  682  is secured to the sun gear member  642 . 
     The stator of the third motor/generator  684  is secured to the transmission housing  660 . The rotor of the third motor/generator  684  is secured to the sun gear member  632 . 
     The hybrid transmission  614  receives power from the engine  12 , and also exchanges power with an electric power source  686 , which is operably connected to a controller  688 . 
     DESCRIPTION OF AN EIGHTH EXEMPLARY EMBODIMENT 
     With reference to  FIG. 8 , a powertrain  710  is shown, including an engine  12  connected to another embodiment of the improved electrically variable transmission (EVT), designated generally by the numeral  714 . Transmission  714  is designed to receive at least a portion of its driving power from the engine  12 . As shown, the engine  12  has an output shaft that serves as the input member  17  of the transmission  714 . A transient torque damper (not shown) may also be implemented between the engine  12  and the input member  17  of the transmission. 
     In the embodiment depicted the engine  12  may be a fossil fuel engine, such as a gasoline or diesel engine which is readily adapted to provide its available power output typically delivered at a selectable number of revolutions per minute (RPM). 
     Irrespective of the means by which the engine  12  is connected to the transmission input member  17 , the transmission input member  17  is operatively connected to a planetary gear set in the transmission  714 . An output member  19  of the transmission  714  is connected to a final drive  16 . 
     The transmission  714  utilizes three differential gear sets, preferably in the nature of planetary gear sets  720 ,  730  and  740 . The planetary gear set  720  employs an outer gear member  724 , typically designated as the ring gear. The ring gear member  724  circumscribes an inner gear member  722 , typically designated as the sun gear. A carrier member  726  rotatably supports a plurality of planet gears  727  such the each planet gear  727  simultaneously, and meshingly engages both the outer, ring gear member  724  and the inner, sun gear member  722  of the planetary gear set  720 . 
     The planetary gear set  730  also employs an outer gear member  734 , typically designated as the ring gear. The ring gear member  734  circumscribes an inner gear member  732 , typically designated as the sun gear. A carrier member  736  rotatably supports a plurality of planet gears  737  such that each planet gear  737  simultaneously, and meshingly engages both the outer, ring gear member  734  and the inner, sun gear member  732  of the planetary gear set  730 . 
     The planetary gear set  740  also employs an outer gear member  744 , typically designated as the ring gear. The ring gear member  744  circumscribes an inner gear member  742 , typically designated as the sun gear. A carrier member  746  rotatably supports a plurality of planet gears  747  such that, each planet gear  747  simultaneously, and meshingly engages both the outer, ring gear member  744  and the inner, sun gear member  742  of the planetary gear set  740 . 
     The input shaft  17  is continuously connected to the carrier member  726 . The output shaft  19  is continuously connected to the carrier member  746 . 
     A first interconnecting member  770  continuously connects the ring gear member  724  with the carrier member  736 . A second interconnecting member  772  continuously connects the sun gear member  722  with the ring gear member  744 . A third interconnecting member  774  continuously connects the ring gear member  734  with the carrier member  746 . 
     A first brake  750  selectively connects the sun gear member  722  and the ring gear member  744  via interconnecting member  772  with the transmission housing  760 . This brake  750  enables series hybrid mode operation in forward and reverse. A second brake  752  selectively connects the sun gear member  742  with the transmission housing  760 . A third brake  754  selectively connects the earner member  736  and the ring gear member  724  via interconnecting member  770  with the transmission housing  760 . 
     The embodiment  710  also incorporates first, second and third motor/generators  780 ,  782  and  784 , respectively. The stator of the first motor/generator  780  is secured to the transmission housing  760 . The rotor of the first motor/generator  780  is secured to the sun gear member  742 . 
     The stator of the second motor/generator  782  is secured to the transmission housing  760 . The rotor of the second motor/generator  782  is secured to the sun gear member  732 . 
     The stator of the third motor/generator  784  is secured to the transmission housing  760 . The rotor of the third motor/generator  784  is secured to the ring gear member  724  and the carrier member  736  via interconnecting member  770 . 
     The hybrid transmission  714  receives power from the engine  12 , and also exchanges power with an electric power source  786 , which is operably connected to a controller  788 . 
     DESCRIPTION OF A NINTH EXEMPLARY EMBODIMENT 
     With reference to  FIG. 9 , a powertrain  810  is shown, including an engine  12  connected to another embodiment of the improved electrically variable transmission (EVT), designated generally by the numeral  814 . Transmission  814  is designed to receive at least a portion of its driving power from the engine  12 . As shown, the engine  12  has an output shaft that serves as the input member  17  of the transmission  814 . A transient torque damper (not shown) may also be implemented between the engine  12  and the input member  17  of the transmission. 
     In the embodiment depicted the engine  12  may be a fossil fuel engine, such as a gasoline or diesel engine which is readily adapted to provide its available power output typically delivered at a selectable number of revolutions per minute (RPM). 
     Irrespective of the means by which the engine  12  is connected to the transmission input member  17 , the transmission input member  17  is operatively connected to a planetary gear set in the transmission  814 . An output member  19  of the transmission  814  is connected to a final drive  16 . 
     The transmission  814  utilizes three differential gear sets, preferably in the nature of planetary gear sets  820 ,  830  and  840 . The planetary gear set  820  employs an outer gear member  824 , typically designated as the ring gear. The ring gear member  824  circumscribes an inner gear member  822 , typically designated as the sun gear. A carrier member  826  rotatably supports a plurality of planet gears  827  such that each planet gear  827  simultaneously, and meshingly engages both the outer, ring gear member  824  and the inner, sun gear member  822  of the planetary gear set  820 . 
     The planetary gear set  830  also employs an outer gear member  834 , typically designated as the ring gear. The ring gear member  834  circumscribes an inner gear member  832 , typically designated as the sun gear. A earner member  836  rotatably supports a plurality of planet gears  837 ,  838  such that each planet gear  837  meshing engages the outer, ring gear member  834  and each planet gear  838  simultaneously, and meshingly engages both the inner, sun gear member  832  and the respective planet gear  837  of the planetary gear set  830 . 
     The planetary gear set  840  also employs an outer gear member  844 , typically designated as the ring gear. The ring gear member  844  circumscribes an inner gear member  842 , typically designated as the sun gear. A carrier member  846  rotatably supports a plurality of planet gears  847  such that each planet gear  847  simultaneously, and meshingly engages both the outer, ring gear member  844  and the inner, sun gear member  842  of the planetary gear set  840 . 
     The input shaft  17  is continuously connected to the ring gear member  824 . The output shaft  19  is continuously connected to the carrier member  846 . 
     A first interconnecting member  870  continuously connects the sun gear member  822  with the ring gear member  834 . A second interconnecting member  872  continuously connects the carrier member  826  with the sun gear member  842 . A third interconnecting member  874  continuously connects the sun gear member  832  with the ring gear member  844 . 
     A brake  850  selectively connects the carrier member  826  with the transmission housing  860 . This brake  850  enables series hybrid operation in forward and reverse. 
     The embodiment  810  also incorporates first, second and third motor/generators  880 ,  882  and  884 , respectively. The stator of the first motor/generator  880  is secured to the transmission housing  860 . The rotor of the first motor/generator  880  is secured to the ring gear member  834  via an offset drive  890 , such as a belt or chain, which may change the speed ratio. 
     The stator of the second motor/generator  882  is secured to the transmission housing  860 . The rotor of the second motor/generator  882  is secured to the carrier member  836 . 
     The stator of the third motor/generator  884  is secured to the transmission housing  860 . The rotor of the third motor/generator  884  is secured to the ring gear member  844  via offset gear  892 , which may change the speed ratio. 
     The hybrid transmission  814  receives power from the engine  12 , and also exchanges power with an electric power source  886 , which is operably connected to a controller  888 . 
     While the best modes for earning 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.