Abstract:
A vehicle powertrain for a hybrid vehicle includes an electronically variable transmission (EVT) with an input member to receive mechanical rotary power from the engine, an output member to provide mechanical rotary power to a vehicle powertrain to propel the vehicle, and an EVT gear train configured to selectively and operatively couple the input member to the output member. The EVT further includes first and second motor/generators driveably coupled to the gear train. A selectively engageable input brake mechanism is provided to create a reaction torque for the motor/generators thereby enabling the motor/generators to be used with additive power for electric propulsion or regenerative braking. The input brake improves electrical power to mechanical power conversion efficiency by reducing power circulation when the EVT is operated in electric drive, engine off mode.

Description:
TECHNICAL FIELD 
       [0001]    The present invention pertains generally to electric hybrid motor vehicles having an engine driving an input member of an electrically variable transmission (EVT) and, more particularly, to an EVT having a selectively operable torque transmitting device or input brake configured to restrain or mechanically ground the rotation of the input member when the vehicle is operating in an engine off, battery only propulsion mode thereby providing a reaction torque enabling the motor/generators to be used with improved electrical power to mechanical power conversion efficiency for electric propulsion or regenerative braking. 
       BACKGROUND OF THE INVENTION 
       [0002]    Internal combustion engines power the majority of motor vehicles. Such engines are typically powered by the combustion of refined oil products such as diesel fuel or gasoline. The dependence on oil for energy and transportation, together with the desire to produce a more fuel efficient vehicle have lead to the development of hybrid vehicles. In the current art, hybrid vehicles are generally equipped with an electrically variable transmission (EVT). EVTs generally have an input shaft driven by the vehicle engine and an output shaft driving or being driven by the vehicle powertrain between the EVT output shaft and the vehicle&#39;s driven wheels. Connecting the input and output shafts within the EVT is a gear train having one or more differential gear sets which are selectively controllable to provide a plurality of EVT transmission operating modes. EVTs are equipped with two or more electric motor/generators, the motor/generators are adapted to provide power to or receive power from the differential gear sets. The motor/generators are connected to a storage battery or batteries in the vehicle and are adapted to receive power from the batteries to power the vehicle (for example, electric only propulsion with the vehicle engine off) or to provide power to the batteries from the drive train (example, when slowing the vehicle through regenerative braking). Examples of suitable storage batteries include lead acid batteries, nickel-metal hydride (NiMH) batteries and lithium ion (Li-Ion) batteries. The motor/generators can transform electrical power from the battery into mechanical power at different torques and speeds to drive the vehicle powertrain or driveably assist the engine during vehicle acceleration for example. Each motor/generator is operatively connected to the differential gear sets of the EVT gear train to provide a range of transmission operation characterized by continuously controllably variable speeds between the input and output shafts of the EVT. EVTs may also incorporate one or more fixed gears which are characterized by a fixed speed and torque relationship between input and output. Hybrid equipped vehicles with electrically variable transmissions are operable in several modes including modes for electric only vehicle drive (engine power off). The inclusion of the electric drive capability in the EVT allows the vehicle engine to be shut off under conditions where it is lightly loaded and inefficient, thereby providing better fuel economy and reduced emissions. 
         [0003]    Modern electrically variable transmissions are generally of the power split transmission type, utilizing differential gearing to achieve continuously variable torque and speed ratios between the EVT input and output. The power split EVT transmission can utilize differential gearing to send a portion of its transmitted power through a pair of motor/generators, the remainder of the stick diagramming through a parallel directly geared path or gear train. 
         [0004]    One form of differential gearing known to those skilled in the art is the planetary gear set. Planetary gear sets consist of a sun gear meshed with and orbited by one or more planetary gears, the planetary gears meshed with a ring gear. Such a combination provides the benefits of compactness and different torque and speed ratios among the members of the gear set. Differential gear sets can be built, without using planetary gear sets, for example by using bevel gears and other gears in an arrangement where the rotation speed of one gear is always a weighted average of the speeds of the other two gear members. 
         [0005]    Hybrid electric vehicles include one or more electric energy storage devices. The typical electric energy device is a chemical storage battery. The storage battery permits the power output from the transmission to vary from the power output of the engine to the transmission, with the battery and motor/generators making up the difference or regeneratively storing the excess as in the case of regenerative vehicle braking. A control unit regulates the stick diagram between the motor/generators and the energy storage device as well as regulating power between the first and second motor/generators. 
         [0006]    One type of EVT is the 2 mode input-compound split type, which contains a first mode input split and a second mode compound split. Operation in first or second variable-speed-ratio modes of operation may be selectively achieved by using torque transfer devices such as friction clutches for example. In the first mode, an input power split ratio is formed by the application of a first clutch and the output speed of the transmission is proportional to the speed of one motor/generator. In a second mode, a compound power split ratio range is achieved by the application of a second clutch and the output speed of the transmission is not proportional to the speed of either motor/generator but is instead proportional to the linear algebraic combination of the speeds of the two motor/generators. EVT operation at a fixed speed ratio may be obtained by operation of both of the clutches. 
         [0007]    An EVT may be operated purely in an electrical only drive mode wherein the engine is in an off condition or mechanically disconnected from the EVT input member. 
       SUMMARY OF THE INVENTION 
       [0008]    A selectively operable torque transmitting device or input brake is provided that can either be incorporated directly into or provided externally to an EVT. The selectively operable torque transmitting device locks the rotation of the EVT input member to a mechanical ground such as the EVT housing to selectively restrain or prevent the rotation of the input member when the vehicle is operating in an engine off, battery only propulsion mode. By restraining the rotation of the EVT input member, the torque transmitting device changes the mechanical configuration of the EVT&#39;s electric power-split hybrid powertrain to improve the electromechanical drive operation and efficiency of the vehicle in using electrical energy supplied from the stored electrical energy source of the vehicle. 
         [0009]    The disclosed invention is advantageously adapted for use with hybrid vehicles having storage batteries configured to be charged from an electrical utility power grid, for example, when the vehicle is parked overnight. By providing the vehicle with batteries having the capacity and configuration to receive and store electrical energy from the electric utility grid, the hybrid vehicle is then usable for an extended range on electric only power (i.e. with the vehicle engine off) resulting in increase fuel savings. Specifically, the electrical energy supplied by the utility to charge the vehicle batteries can be utilized with higher efficiency when propelling the vehicle using the EVT&#39;s electric motors only (engine off) and thereby achieve greater driving range from the stored energy, if a torque transmitting device is applied to selectively ground or prevent the rotation of the EVT input member. The torque transmitting device is controllably operable to ground rotation of the EVT input member, thereby changing the mechanical configuration of the power-split transmission to a fixed gear ratio between one or both EVT motors and the output member of the transmission and eliminating power circulation and drive inefficiencies as discussed below. 
         [0010]    The torque transmitting device operable to ground rotation of the EVT input member may also be applied to improve the efficiency of the usage of stored electric power by the EVT motors when reversing the vehicle in an electric only mode. The efficiency is realized by providing a reaction torque at the EVT input member so that the motor/generators can develop torque against the locked input shaft, eliminating the need for one of the electric motors to rotate or motor the vehicle engine while developing reaction torque for the other motor/generator. 
         [0011]    Exemplary devices for selectively locking the rotation of the EVT input member to ground include an electromagnetic clutch configured to selectively lock the EVT input member and a hydraulically actuated disk brake configured to selectively lock the EVT input member, as well as various known types of wet or dry friction clutches. 
         [0012]    The above features and advantages as well as other features and advantages of the present invention will be 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 
         [0013]      FIG. 1  is a schematic stick diagram representation of a two mode input/compound split, electrically variable transmission for a hybrid motor vehicle equipped with an input brake in accordance with the disclosed invention; 
           [0014]      FIG. 2  is a schematic stick diagram representation of another embodiment of a two mode input/compound split, electrically variable transmission for a hybrid motor vehicle equipped with an input brake in accordance with the disclosed invention; 
           [0015]      FIG. 3  is a schematic stick diagram representation of an alternate variation of the two mode input/compound split, electrically variable transmission depicted in  FIG. 2 , in accordance with the disclosed invention; and 
           [0016]      FIG. 4  is a schematic stick diagram representation of yet another embodiment of the two mode input/compound split, electrically variable transmission for a hybrid motor vehicle equipped with an input brake in accordance with the disclosed invention. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0017]    Referring to the drawings wherein like characters represent the same or corresponding parts throughout the several views, there is shown in  FIG. 1  a schematic stick diagram representation of a two mode input/compound split, electrically variable transmission (EVT)  10  for a hybrid motor vehicle (not shown) equipped with an input torque transfer device consisting of an input brake  12  and/or one way clutch  66  in accordance with the disclosed invention. It should be appreciated that the illustrated electrically variable transmission is just one specific embodiment of a two mode input/compound split EVT with which the input brake  12  and/or one-way clutch  66  may be advantageously applied. In all embodiments disclosed and illustrated herein, it is to be understood that the input torque transfer device may comprise either the input brake  12  or one-way clutch  66 , or both the input brake  12  and one-way clutch  66  in combination. The one way clutch  66  permits the input member  14  to rotate in a positive direction as normally driven by the engine  80  while preventing the input member  14  from rotating in a negative direction. The input brake  12  to ground  58  is selectively operable by the control unit  86  to resist rotation of the input member  14  by frictionally braking the input member  14  to ground  58 . These features pertain to all descriptions and illustrations of various embodiments presented herein. 
         [0018]    The EVT  10  includes an input member  14  through which mechanical rotary power is delivered to the EVT from a mechanical power source such as a gasoline or diesel engine (not shown). The input member  14 , in some embodiments, may comprise a driven shaft mechanically connecting the input member  14  to the engine. 
         [0019]    The electrically variable transmission illustrated in  FIG. 1  utilizes three differential gear sets  16 ,  18  and  20 , each having a first gear member, a second gear member and a third gear member. The differential gear sets  16 ,  18  and  20  are preferably planetary gear sets  16 ,  18  and  20 . The first planetary gear set  16  employs an outer gear member  22 , typically designated as the ring gear. The ring gear  22  circumscribes an inner gear member  24 , typically designated as the sun gear. A carrier  26  rotatably supports a plurality of planet gears  28  such that each planet gear  28  meshingly engages both the outer, ring gear member  22  and the inner, sun gear member  24  of the first planetary gear set  16 . The input member  14  is secured to the ring gear member  22  of the planetary gear set  16 . 
         [0020]    The planetary gear set  18  also has an outer gear member  30 , often designated as the ring gear, that circumscribes an inner gear member  31 , often designated as the sun gear. A plurality of planet gears  34  are also rotatably mounted in a carrier  32  such that each planet gear member  34  simultaneously, and meshingly, engages both the outer, ring gear member  30  and the inner, sun gear member  31  of the planetary gear set  18 . 
         [0021]    The planetary gear set  20  also has an outer gear member  36 , also designated as the ring gear, that circumscribes an inner gear member  38 , often designated as the sun gear. A plurality of planet gears  42  are also rotatably mounted in a carrier  40  such that each planet gear member  42  simultaneously, and meshingly, engages both the outer, ring gear member  36  and the inner, sun gear member  38  of the planetary gear set  20 . 
         [0022]    A first interconnecting member  44  continuously connects the sun gear  24  of the planetary gear set  16  with the ring gear  30  of the planetary gear set  18 . The first gear set  16  and the second gear set  18  are compounded by a second interconnecting member  46  continuously connecting the carrier  26  of the planetary gear set  16  with the carrier  32  of the planetary gear set  18 . A third interconnecting member  48  continuously connects the sun gear  31  of the planetary gear set  18  with the sun gear  38  of the planetary gear set  20 . 
         [0023]    The EVT  10  also includes electric motor/generator ‘A’  50  and electric motor/generator ‘B’  52 . The stator of the first motor/generator  50  is secured to the transmission housing (not shown). The rotor of the first motor/generator  50  is secured to the first interconnecting member  44 . 
         [0024]    The stator of the second motor/generator  52  is also secured to the transmission housing (not shown). The rotor of the second motor/generator  52  is secured to the third interconnecting member  48 . 
         [0025]    A first torque transfer device, such as a clutch  54 , selectively connects the ring gear  30  of the planetary gear set  18  to the sun gear  31  of the planetary gear set  18 , thereby mechanically locking the rotation of the sun gear  31 , planetary gears  34 , carrier  32  and ring gear  30  to rotate together with the same rotational speed. 
         [0026]    A second torque transfer device, such as brake  56 , selectively connects the sun gear  31  of the planetary gear set  18  with the ground  58 , such as the transmission housing. Activating or engaging the clutch  56  locks or grounds the sun gear  31  of planetary gear set  18  and the rotor  70  of motor/generator  52  to ground. 
         [0027]    A third torque transfer device, such as brake  60 , selectively connects the ring gear  36  of the planetary gear set  20  with the ground  58 , such as the transmission housing. That is, the ring gear  36  is selectively secured against rotation by an operative connection to the non-rotatable ground  58 . 
         [0028]    The first, second and third torque transfer devices  54 ,  56  and  60  are employed to assist in the selection of the operational modes of the hybrid EVT transmission  10 , as will be hereinafter more fully explained at least as pertains to the electric only engine off EVT operation modes pertinent to the present invention. 
         [0029]    The output drive member  62  of the EVT  10  is secured to the carrier  40  of the planetary gear set  20 . 
         [0030]    A fourth torque transfer device, such as clutch  64 , selectively connects the second interconnecting member  46  to the output member  62 . 
         [0031]    The first, second, third and fourth torque transfer devices  54 ,  56 ,  60  and  64  are employed to assist in the selection of the operational modes of the hybrid EVT transmission  10 . 
         [0032]    A control unit  86  regulates the motor speed and torque of motor/generators  50  and  52 . Torque transfer devices  12 ,  54 ,  60  and  64  are selectively controlled by control unit  86  to configure the EVT into various operation modes. The control unit  86  is electrically interfaced to the electrical energy storage device such as a battery  88 . 
         [0033]    An input torque transfer device, such as the input brake  12 , selectively locks the EVT input member  14  to the ground, such as the transmission housing. The input torque transfer device  12  is locked only when the vehicle engine  80  is not running. By locking the input member  14  against rotation, the EVT  10  is adapted for efficient operation in one or more battery only fixed gear modes. These modes allow both motors  50  and  52  to be used with additive power to maximize the utilization of the designed motor capacity for electric propulsion or regenerative braking, as described below. 
         [0034]    The electrically variable transmission  10 , as illustrated in  FIG. 1 , is a two mode input/compound split EVT having an input split low range and a compound split high range. Typically, the input split range is used for electric only propulsion mode (vehicle engine off), however, this results in motor/generator  52  spinning at a high negative speed. In an EVT transmission without the input brake  12  of the present invention, operation at compound split range with the engine  80  at zero speed requires motor/generator  52  to operate as a generator when motor/generator  50  is operating as a motor to propel the vehicle or requiring motor/generator  52  to operate as a motor whenever motor/generator  50  is generating electric power. This interaction between motor/generators  50  and  52  results in poor energy efficiency and limits the usefulness of the compound split range for electric only operation. However, if the input member of the EVT is locked or braked as by torque transfer or input brake device  12 , then an additional torque reaction point is added at the EVT input member node allowing the torques on motor/generators  50  and  52  to be controlled independently. In this case, motor/generator  52  can supply power additively to motor/generator  50 , eliminating circulating power and improving efficiency. With the presence of the input torque transfer device or input brake  12 , the compound split range now has high torque capacity as the torques of motors  50  and  52  are additive through gear ratios to the output member  62 , through two new transmission modes EV 1  and EV 2  as discussed more fully below. 
         [0035]    The clutch states required to actuate the electric drive only EVT transmission modes together with the use of input brake  12  in enabling these new modes will now be discussed. As discussed earlier, the addition of the input brake  12  to the two mode input/compound split EVT provides additional electric only propulsion, engine off, fixed gear ratio modes of operation of the hybrid vehicle EVT. Two of the possible electric only propulsion EVT fixed gear ratio modes are presented herein, the first is the “EV low” (EV 1 ) mode, and the second is the “EV high” (EV 2 ) mode. Referring again to  FIG. 1 , both modes EV 1  and EV 2  require the engine  80  to be in an off state with the torque transfer device or input brake  12  to be engaged, thereby grounding the input member  14  to prevent the rotation of input member  14 . As discussed earlier, this provides another torque reaction point to the EVT and, in particular, lock or inhibits the rotation of ring gear  22  of the planetary gear set  16  (using the specific example of  FIG. 1 ). This enforces a fixed gearing ratio between the rotor of motor/generator  50  through the sun gear  24  and the planetary gears  28 . 
         [0036]    To enable the “EV low” (EV 1 ) electric only propulsion EVT fixed gear ratio mode, the following clutches and brake are engaged or locked: brake  60  and torque transmission device/input brake  12 . The remaining torque transfer devices  64 ,  56  and  54  are disengaged. Brake  60  locks the ring gear  36  of planetary gear set  20  to ground, thereby enforcing a fixed gear ratio between the rotor  70  of motor/generator  52  and the EVT output member  62 . Similarly, the input brake  12  enforces a fixed gear ratio between the rotor  68  of motor/generator  50  and the rotation of the second interconnecting member  46  which connects to and drives the planetary gears  34  of the planetary gear set  18 . The rotor  68  of motor/generator  50  also drives the ring gear  30  of planetary gear set  18 . As the ring gear  30  and planetary gears  34  are both driven by motor/generator  50 , a fixed gearing ratio is enforced between the rotational speed of rotor  68  of motor/generator  50  and the rotor  70  of motor/generator  52 . As discussed above, rotor  70  of motor/generator  52  drives the EVT output member  62  at a fixed gear ratio due to the locked state of brake  60 . As can be understood from the above, motor/generators  50  and  52  are driveably geared by separate fixed ratios to the transmission output member  62 . 
         [0037]    To enable the “EV high” (EV 2 ) electric only propulsion EVT fixed gear ratio mode, the following clutches and brakes are engaged or locked: clutch  64  and torque transmission device/input brake  12  (illustrative element numbers specific to the EVT embodiment  10  depicted in  FIG. 1 ). The remaining torque transfer devices  60 ,  56  and  54  are disengaged. Clutch  64  locks the rotation of the planetary gears  42  of planetary gear set  20  to the rotation of the planetary gears  28  of planetary gear set  16 . The input brake  12  enforces a fixed gear ratio between the rotor  68  of motor/generator  50  and the rotation of the second interconnecting member  46  which driveably connects directly to the output member  62  through engaged clutch  64 . Rotor  70  of motor/generator  52  drives the sun gear  31  of planetary gear set  18 . Rotor  68  of motor/generator  50  drives the ring gear  30  of planetary gear set  18  and also drives the planetary gears  34  at a fixed gear ratio determined by the planetary gears  28  and sun gear  24  of the planetary gear set  16 . The rotation speed ratio between the ring gear  30  and the planetary gears  34  being fixed, as just described, enforces a fixed gear ratio between the rotation speeds of rotors  68  and  70  of motor/generators  50  and  52 . Motor/generator  52  delivers power to output member  62  through the sun gear  31  and planetary gears  34  of planetary gear set  18 . As can be understood from the above, motor/generators  50  and  52  are driveably geared by separate fixed ratios to the transmission output member  62 . 
         [0038]    As can be understood from the above discussion, electric drive only EVT transmission modes EV 1  and EV 2  permit both motor/generators  50  and  52  to be operated in motoring mode to produce mechanical power which is additively combined for electric propulsion, maximizing the designed motor capacity for electric propulsion. Similarly, modes EV 1  and EV 2  enable motor/generators  50  and  52  to operate with additive generating power to maximize utilization of the designed motor capacity for regenerative braking. These fixed gear additive modes are enabled through the addition of the input brake  12  which locks the input member  14  providing a torque reaction point at the EVT input to facilitate these modes as described above. The addition of the torque transmission device or input brake  12  of the present invention eliminates circulating power and improves operating and energy efficiency of the EVT in electric only modes (engine off) thereby yielding measurable benefits in increased efficiency in electric to mechanical energy conversion and increased available electric drive torque. 
         [0039]    If the input brake  12  is capable of lockably preventing the rotation of the input member  14  in both the positive and negative directions, then the hybrid vehicle EVT system is capable of both motoring and regenerative braking in the EV 1  and EV 2  modes. The torque transfer device or input brake  12  may be realized as a wet friction clutch, dry friction clutch, dog clutch, or pawl mechanism as just a few examples. The input brake  12  may also be implemented as a one way clutch  66  to ground  58 , since the engine  80  is not required to spin in the reverse direction. In this case (without the input brake  12 ), the improved efficiency and torque capacity is provided for motoring torque at the output, but power circulation is still required for braking torque at the output. Additionally, the input brake  12  may be implemented as a mechanism known as a controllable one way clutch with two modes. In the first mode, the mechanism operates as a conventional one way clutch  66 , allowing the engine  80  to free spin as long as it is in the positive direction. If the speed of the engine  80  reaches zero, the one way clutch  66  engages, preventing the engine  80  from rotating backwards. In the second mode, the one way clutch  66  mechanism locks, preventing input member  14  rotation in either direction. The mechanism may be transitioned between modes whenever the engine  80  speed is zero. This implementation is capable of providing full functionality for both motoring and regenerative braking. 
         [0040]    The EVT has several other modes, specifically engine running modes, which are not discussed herein as these additional modes are known to those skilled in the art and while important to the functioning of the EVT, are not relevant to the understanding of the present invention. 
         [0041]    Turning now to  FIG. 2  wherein like numbers are used to refer to like components.  FIG. 2  is a schematic stick diagram representation of another embodiment of a two mode input/compound split, electrically variable transmission  72  for a hybrid motor vehicle equipped with an input brake  112  and/or one way clutch  166  in accordance with the disclosed invention. It is to be understood that wherever the input brake  112  is discussed below, the input brake  112  can be replaced with the one-way clutch  166  to achieve the EV 1  and EV 2  electric only drive modes discussed below. The one-way clutch  166  is operable to lock the input member  14  from rotating in a counter to normal engine operation direction, thereby locking the input member  14  to ground when the vehicle is operated in electric only propulsion modes EV 1  or EV 2 . It should be appreciated that the illustrated electrically variable transmission  72  is just one specific embodiment of a two mode input/compound split EVT with which the input brake  112  and/or one-way clutch  166  may be advantageously applied. The one way clutch  166  permits the input member  14  to rotate in a positive direction as normally driven by the engine  80  while preventing the input member  14  from rotating in a negative direction. The input brake  112  to ground  158  is selectively operable by the control unit  186  to resist rotation of the input member  14  by frictionally braking the input member  14  to ground. 
         [0042]    EVT  72  includes an input member  14  through which mechanical rotary power is delivered to the EVT  72  from a mechanical power source such as a gasoline or diesel engine  80 . The input member  14 , in some embodiments, may comprise a driven shaft mechanically connecting the input member  14  to the engine  80 . 
         [0043]    The electrically variable transmission as illustrated in  FIG. 2  utilizes two differential gear sets, preferably planetary gear sets  116  and  118 . The first planetary gear set  116  employs an outer gear member  122 , typically designated as the ring gear. The ring gear  122  circumscribes an inner gear member  124 , typically designated as the sun gear. In  FIG. 2  this is a compound planetary gear set. In  FIG. 2 , the planetary gear set  116  has an outer ring gear member  122 , that circumscribes an inner gear member typically designated as a sun gear  124 . A plurality of planet gears  127 ,  128  are also rotatably mounted in a carrier  126  such that each planet gear member  127  meshingly engages the sun gear  124  and each planet gear member  128  simultaneously and meshingly engages the ring gear member  122  of the planetary gear set  116 . The input member  14  is secured to the ring gear member  122  of the planetary gear set  116 . 
         [0044]    The planetary gear set  118  also has an outer gear member  130 , often also designated as the ring gear, which circumscribes an inner gear member  131 , also often designated as the sun gear. A plurality of planet gears  134  are also rotatably mounted in a carrier  132  such that each planet gear member  134  simultaneously and meshingly engages both the outer, ring gear member  130  and the inner, sun gear member  131  of the planetary gear set  118 . In EVT  72  the input member  14  is driveably connected to the ring gear  122  of planetary gear set  116 . 
         [0045]    A first torque transfer device  154 , such as a clutch, selectively connects the input member  14  to the carrier  126  of planetary gear set  116  thereby mechanically locking the rotation of the input member  14  and carrier  126 , resulting in a fixed gear ratio between the input member  14  and the rotor  168  of motor/generator  150 . The sun gear  124  of planetary gear set  116  is continuously connected to the rotor  168  of motor/generator  150 . 
         [0046]    A second torque transfer device  164 , such as a clutch, selectively connects the rotor  168  of motor/generator  150  to the ring gear  130  of the planetary gear set  118 . 
         [0047]    A third torque transfer device, such as brake  160 , selectively connects the ring gear  130  of the planetary gear set  118  with the ground  158 , such as the transmission housing. That is, the ring gear  130  is selectively secured against rotation by an operative connection to the non-rotatable ground  158 . The carrier member  132  of planetary gear set  118  is continuously connected to the output member  62 . The sun gear  131  of planetary gear set  118  is continuously connected to the rotor  170  of motor/generator  152 . 
         [0048]    A fourth torque transfer device  156 , such as a brake, selectively connects the rotor  170  and sun gear  131  to ground  58  preventing their rotation. 
         [0049]    A control unit  186  regulates the motor speed and torque of motor/generators  150  and  152 . Torque transfer devices  112 ,  154 ,  160  and  164  are selectively controlled by control unit  186  to configure the EVT into various operation modes. The control unit  186  is electrically interfaced to the electrical energy storage device such as a battery  188 . 
         [0050]    Similar to the earlier discussion of EVT  10  presented in  FIG. 1 , in  FIG. 2  the torque transfer devices  154 ,  156 ,  160  and  164  are employed to assist in the selection of the operational modes of the hybrid EVT transmission  72 , as will be hereinafter more fully explained. 
         [0051]    Similar to the earlier discussion concerning  FIG. 1 , electrically variable transmission  72  is a two mode input/compound split EVTs having an input split low range and a compound split high range. Typically, the input split range is used for electric only propulsion mode (vehicle engine off), however, this results in motor/generator  152  spinning at a high negative speed. In an EVT transmission without the input brake  112  of the present invention, operation at compound split range with the engine  80  at zero speed requires motor/generator  152  to operate as a generator when motor/generator  150  is motoring to propel the vehicle or requiring motor/generator  152  to operate as a motor whenever motor/generator  150  is generating electric power. This interaction between motor/generators  150  and  152  results in poor efficiency and limits the usefulness of the compound split range for electric only operation, as discussed earlier. However, if the input member  14  of EVT  72  is locked or braked as by torque transfer or input brake device  112 , then an additional torque reaction point is added at the EVT input member  14  allowing the torques on motor/generators  150  and  152  to be controlled independently. In this case, motor/generator  152  can supply power additively to motor/generator  150 , eliminating circulating power and improving efficiency. With the presence of the input brake  112 , the compound split range now has high torque capacity as the torques of motors  150  and  152  are additive through gear ratios to the output  62 , through two new modes EV 1  and EV 2  as discussed below. 
         [0052]    The clutch states required to actuate the electric drive only EVT transmission modes enabled together with the use of input brake  112  will now be discussed. As discussed earlier, the addition of the input brake  112  to the two mode input/compound split EVT  72  provides additional electric only propulsion, engine off, fixed gear ratio modes of operation of the hybrid vehicle EVT  72 . Two of the possible electric only propulsion EVT fixed gear ration modes are presented herein, the first is the “EV low” (EV 1 ) mode, and the second is the “EV high” (EV 2 ) mode. Referring again to  FIG. 2 , both modes EV 1  and EV 2  require the engine  80  to be in an off state with the torque transfer device or input brake  112  to be engaged, thereby grounding the input member  14  to prevent the rotation of input member  14 . As discussed earlier, this provides another torque reaction point to the EVT  72  and, in particular, lock or inhibits the rotation of either the ring gear  122 . This enforces a fixed gearing ratio between the rotor  168  of motor/generator  150  and the input member  14  through the planetary gear set  116 . 
         [0053]    To enable the “EV low” (EV 1 ) electric only propulsion EVT fixed gear ratio mode, the following torque transfer devices are engaged or locked: brake  160  and torque transmission device/input brake  112 . The remaining torque transfer devices  164 ,  156  and  154  are disengaged. Brake  160  locks the ring gear  130  of planetary gear set  118  to ground  158 , thereby enforcing a fixed gear ratio between the rotor  170  of motor/generator  152  and the EVT output member  62 . 
         [0054]    Similarly, the input brake  112  enforces a fixed gear ratio between the rotor  168  of motor/generator  150  and the rotation of the sun gear  131  by locking a member of the planetary gear set  116  to ground  158 . In  FIG. 2  EVT  72 , input brake  112  locks ring gear  122  to ground  158 . In this configuration, motor/generator  150  drives the sun gear  131  through planetary gear set  116  at a fixed gear ratio. Motor/generator  152  also drives sun gear  131 . Both  150  and  152  then drive the output member  62  at a fixed gear ratio through planetary gear set  118 . As can be understood from the above, motor/generators  150  and  152  are driveably geared by separate fixed ratios to the transmission output member  62 . 
         [0055]    To enable the “EV high” (EV 2 ) electric only propulsion EVT fixed gear ratio mode, the following torque transfer devices are engaged or locked: clutch  164  and torque transmission device/input brake  112 . The remaining torque transfer devices  160 ,  156  and  154  are disengaged. Clutch  164  locks the rotation of the rotor  168  of motor/generator  150  to the ring gear  130  of planetary gear set  118 . As discussed above, input brake  112  enforces a fixed gear ratio between the rotor  168  of motor/generator  150  and the rotation of the sun gear  131  by locking a member of the planetary gear set  116  to ground  158 . The rotation speed ratio between the rotor  168  of motor/generator  150  and the rotor  170  of motor/generator  152  is a fixed value due to the locking action of input brake  112  on planetary gear set  116  as described above. Motor/generator  152  delivers power to output member  62  through the sun gear  131  and planetary gears  134  of planetary gear set  118 . Motor/generator  150  delivers power to output member  62  through the ring gear  130  and planetary gears  134  of planetary gear set  118 , providing an output speed proportional to the speed of the two motor/generators  150  and  152 . 
         [0056]    As discussed earlier with  FIG. 1 , electric drive only EVT transmission modes EV 1  and EV 2  permit both motor/generators  150  and  152  to be operated in motoring mode to produce mechanical power which is additively combined or electric propulsion, maximizing the designed motor capacity for electric propulsion. Similarly, modes EV 1  and EV 2  enable motor/generators  150  and  152  to operate with additive generating power to maximize utilization of the designed motor capacity for regenerative braking. These fixed gear additive modes are enabled through the addition of the input brake device  112  which locks the input member  14  to facilitate these modes as described above. The addition of the torque transmission device or input brake  112  of the present invention eliminates circulating power and improves operating and energy efficiency of the EVT  72  in electric only modes (engine off) as described above. 
         [0057]    EVT  72  has several ‘engine on’ modes which are not discussed herein as these additional modes are known to those skilled in the art and are not essential or relevant to the understanding of the present invention which is directed to engine off electric only EVT operation. 
         [0058]    Turning now to  FIG. 3  wherein like numbers are used to refer to like components.  FIG. 3  is a schematic stick diagram representation of an alternate version of the EVT  72  illustrated and discussed earlier with in  FIG. 2 . In  FIG. 3 , electrically variable transmission  74  for a hybrid motor vehicle is equipped with an input brake  212  and/or one way clutch  266  in accordance with the disclosed invention. It is to be understood that wherever the input brake  212  is discussed below, the input brake  212  can be replaced with the one-way clutch  266  to achieve the EV 1  and EV 2  electric only drive modes discussed below. The one-way clutch  266  is operable to lock the input member  14  from rotating in a counter to normal engine operation direction, thereby locking the input member  14  to ground when the vehicle is operated in electric only propulsion modes EV 1  or EV 2 . It should be appreciated that the illustrated electrically variable transmission  74  is just one specific embodiment of a two mode input/compound split EVT with which the input brake  212  and/or one-way clutch  266  may be advantageously applied. The one way clutch  266  permits the input member  14  to rotate in a positive direction as normally driven by the engine  80  while preventing the input member  14  from rotating in a negative direction. The input brake  212  to ground  258  is selectively operable by the control unit  286  to resist rotation of the input member  14  by frictionally braking the input member  14  to ground. 
         [0059]    EVT  74  includes an input member  14  through which mechanical rotary power is delivered to the EVT  74  from a mechanical power source such as a gasoline or diesel engine  80 . The input member  14 , in some embodiments, may comprise a driven shaft mechanically connecting the input member  14  to the engine  80 . 
         [0060]    The electrically variable transmission as illustrated in  FIG. 3  utilize two differential gear sets, preferably planetary gear sets  216  and  218 . The first planetary gear set  216  employs an outer gear member  222 , typically designated as the ring gear. The ring gear  222  circumscribes an inner gear member  224 , typically designated as the sun gear. In  FIG. 3 , this is a simple planetary gearset, while in previously discussed  FIG. 2  this was a compound planetary gearset. In  FIG. 3 , a carrier  226  rotatably supports a plurality of planet gears  228  such that each planet gear  228  meshingly engages both the outer, ring gear member  222  and the inner, sun gear member  224  of the first planetary gear set  216 . The input member  14  is secured to the carrier  226  of the planetary gear set  216 . 
         [0061]    The planetary gear set  218  also has an outer gear member  230 , often also designated as the ring gear, which circumscribes an inner gear member  231 , also often designated as the sun gear. A plurality of planet gears  234  are also rotatably mounted in a carrier  232  such that each planet gear member  234  simultaneously and meshingly engages both the outer, ring gear member  230  and the inner, sun gear member  231  of the planetary gear set  218 . 
         [0062]    Previously discussed EVT  72  ( FIG. 2 ) and EVT  74  differs in where mechanical power from input member  14  is delivered to the planetary gear set  216  ( 116  in  FIG. 2 ). In EVT  72  the input member  14  is driveably connected to the ring gear  122  of planetary gear set  116 . In  FIG. 3 , EVT  74 , the input member  14  is driveably connected to the carrier  226  of planetary gear set  216 . 
         [0063]    A first torque transfer device  254 , such as a clutch, selectively connects the input member  14  to the carrier  226  of planetary gear set  216  thereby mechanically locking the rotation of the input member  14  and carrier  226 , resulting in a fixed gear ratio between the input member  14  and the rotor  268  of motor/generator  250 . The sun gear  224  of planetary gear set  216  is continuously connected to the rotor  268  of motor/generator  250 . 
         [0064]    A second torque transfer device  264 , such as a clutch, selectively connects the rotor  268  of motor/generator  250  to the ring gear  230  of the planetary gear set  218 . 
         [0065]    A third torque transfer device, such as brake  260 , selectively connects the ring gear  230  of the planetary gear set  218  with the ground  258 , such as the transmission housing. That is, the ring gear  230  is selectively secured against rotation by an operative connection to the non-rotatable ground  258 . The carrier  232  of planetary gear set  218  is continuously connected to the output member  62 . The sun gear  231  of planetary gear set  218  is continuously connected to the rotor  270  of motor/generator  252 . 
         [0066]    A fourth torque transfer device  256 , such as a brake, selectively connects the rotor  270  and sun gear  231  to ground  258  preventing their rotation. 
         [0067]    A control unit  286  regulates the motor speed and torque of motor/generators  250  and  252 . Torque transfer devices  212 ,  254 ,  260  and  264  are selectively controlled by control unit  286  to configure the EVT into various operation modes. The control unit  286  is electrically interfaced to the electrical energy storage device such as a battery  288 . 
         [0068]    Similar to the earlier discussion of EVT  72  presented in  FIG. 2 , in  FIG. 3  torque transfer devices  254 ,  256 ,  260  and  264  are employed to assist in the selection of the operational modes of the hybrid EVT transmission  74 , as will be hereinafter more fully explained. 
         [0069]    Similar to the earlier discussion concerning  FIG. 2 , electrically variable transmission  74  is a two mode input/compound split EVTs having an input split low range and a compound split high range. Typically, the input split range is used for electric only propulsion mode (vehicle engine off), however, this results in motor/generator  252  spinning at a high negative speed. In an EVT transmission without the input brake  212  of the present invention, operation at compound split range with the engine  80  at zero speed requires motor/generator  252  to operate as a generator when motor/generator  250  is motoring to propel the vehicle or requiring motor/generator  252  to operate as a motor whenever motor/generator  250  is generating electric power. This interaction between motor/generators  250  and  252  results in poor efficiency and limits the usefulness of the compound split range for electric only operation, as discussed earlier. However, if the input member  14  of EVT  74  is locked or braked as by torque transfer or input brake device  212 , then an additional torque reaction point is added at the EVT input member  14  allowing the torques on motor/generators  250  and  252  to be controlled independently. In this case, motor/generator  252  can supply power additively to motor/generator  250 , eliminating circulating power and improving efficiency. With the presence of the input brake  212 , the compound split range now has high torque capacity as the torques of motors  250  and  252  are additive through gear ratios to the output  62 , through two new modes EV 1  and EV 2  as discussed below. 
         [0070]    The clutch states required to actuate the electric drive only EVT transmission modes enabled together with the use of input brake  212  will now be discussed. As discussed earlier, the addition of the input brake  212  to the two mode input/compound split EVT  74  provides additional electric only propulsion, engine off, fixed gear ratio modes of operation of the hybrid vehicle EVT  74 . Two of the possible electric only propulsion EVT fixed gear ration modes are presented herein, the first is the “EV low” (EV 1 ) mode, and the second is the “EV high” (EV 2 ) mode. Referring again to  FIG. 3 , both modes EV 1  and EV 2  require the engine  80  to be in an off state with the torque transfer device or input brake  212  to be engaged, thereby grounding the input member  14  to prevent the rotation of input member  14 . As discussed earlier, this provides another torque reaction point to the EVT  74  and, in particular, lock or inhibits the rotation of the carrier  226 . This enforces a fixed gearing ratio between the rotor  268  of motor/generator  250  and the input member  14  through the planetary gear set  216 . 
         [0071]    To enable the “EV low” (EV 1 ) electric only propulsion EVT fixed gear ratio mode, the following clutches and brake are engaged or locked: brake  260  and torque transmission device/input brake  212 . The remaining torque transfer devices  264 ,  256  and  254  are disengaged. Brake  260  locks the ring gear  230  of planetary gear set  218  to ground  258 , thereby enforcing a fixed gear ratio between the rotor  270  of motor/generator  252  and the EVT output member  62 . 
         [0072]    Similarly, the input brake  212  enforces a fixed gear ratio between the rotor  268  of motor/generator  250  and the rotation of the sun gear  231  by locking a member of the planetary gear set  216  to ground  258 . In  FIG. 3 , EVT  74 , input brake  212  locks carrier  226  to ground  258 . In this configuration, motor/generator  250  drives the sun gear  231  through planetary gear set  216  at a fixed gear ratio. Motor/generator  252  also drives sun gear  231 . Both motor/generators  250  and  252  then drive the output member  62  at a fixed gear ratio through planetary gear set  218 . As can be understood from the above, motor/generators  250  and  252  are driveably geared by separate fixed ratios to the transmission output member  62 . 
         [0073]    To enable the “EV high” (EV 2 ) electric only propulsion EVT fixed gear ratio mode, the following clutches and brakes are engaged or locked: clutch  264  and torque transmission device/input brake  212 . The remaining torque transfer devices  260 ,  256  and  254  are disengaged. Clutch  264  locks the rotation of the rotor  268  of motor/generator  250  to the ring gear  230  of planetary gear set  218 . As discussed above, input brake  212  enforces a fixed gear ratio between the rotor  268  of motor/generator  250  and the rotation of the sun gear  231  by locking a member of the planetary gear set  216  to ground  258 . The rotation speed ratio between the rotor  268  of motor/generator  250  and the rotor  270  of motor/generator  252  is a fixed value due to the locking action of input brake  212  on planetary gear set  216  as described above. Motor/generator  252  delivers power to output member  62  through the sun gear  231  and planetary gears  234  of planetary gear set  218 . Motor/generator  250  delivers power to output member  62  through the ring gear  230  and planetary gears  234  of planetary gear set  218 , providing an output speed proportional to the speed of the two motor/generators  250  and  252 . 
         [0074]    As discussed earlier with  FIGS. 1 and 2 , electric drive only EVT transmission modes EV 1  and EV 2  permit both motor/generators  250  and  252  to be operated in motoring mode to produce mechanical power which is additively combined or electric propulsion, maximizing the designed motor capacity for electric propulsion. Similarly, modes EV 1  and EV 2  enable motor/generators  250  and  252  to operate with additive generating power to maximize utilization of the designed motor capacity for regenerative braking. These fixed gear additive modes are enabled through the addition of the input brake device  212  which locks the input member  14  to facilitate these modes as described above. The addition of the torque transmission device or input brake  212  of the present invention eliminates circulating power and improves operating and energy efficiency of the EVT  72  or  74  in electric only modes (engine off) as described above. 
         [0075]    EVT  74  has several ‘engine on’ modes which are not discussed herein as these additional modes are known to those skilled in the art and are not essential or relevant to the understanding of the present invention which is directed to engine off electric only EVT operation. 
         [0076]    Turning now to  FIG. 4  wherein like numbers are used to refer to like components.  FIG. 4  is a schematic stick diagram representation of another embodiment of a two mode input/compound split, electrically variable transmission  78  for a hybrid motor vehicle equipped with an input brake  312  and/or one way clutch  366  in accordance with the disclosed invention. It is to be understood that wherever the input brake  312  is discussed below, the input brake  312  can be replaced with the one-way clutch  366  to achieve the EV 1  and EV 2  electric only drive modes discussed below. The one-way clutch  366  is operable to lock the input member  14  from rotating in a counter to normal engine operation direction, thereby locking the input member  14  to ground when the vehicle is operated in electric only propulsion modes EV 1  or EV 2 . It should be appreciated that the illustrated electrically variable transmission  78  is just one specific embodiment of a two mode input/compound split EVT with which the input brake  312  and/or one-way clutch  366  may be advantageously applied. The one way clutch  366  permits the input member  14  to rotate in a positive direction as normally driven by the engine  80  while preventing the input member  14  from rotating in a negative direction. The input brake  312  to ground  358  is selectively operable by the control unit  386  to resist rotation of the input member  14  by frictionally braking the input member  14  to ground. 
         [0077]    The EVT  78  includes an input member  14  through which mechanical rotary power is delivered to the EVT  78  from a mechanical power source such as a gasoline or diesel engine  80 . The input member  14 , in some embodiments, may comprise a driven shaft mechanically connecting the input member  14  to the engine  80 . 
         [0078]    The electrically variable transmission as illustrated in  FIG. 4  utilizes two differential gear sets, preferably planetary gear sets  316  and  318 . The first planetary gear set  316  employs an outer gear member  322 , typically designated as the ring gear. The ring gear  322  circumscribes an inner gear member  324 , typically designated as the sun gear. A carrier  326  rotatably supports a plurality of planet gears  328  such that each planet gear  328  meshingly engages both the outer, ring gear member  322  and the inner, sun gear member  324  of the first planetary gear set  316 . The input member  14  is secured to the ring gear member  322  of the planetary gear set  316 . 
         [0079]    The planetary gear set  318  also has an outer gear member  330 , often also designated as the ring gear, which circumscribes an inner gear member  331 , also often designated as the sun gear. A plurality of planet gears  334  are also rotatably mounted in a carrier  332  such that each planet gear member  334  simultaneously and meshingly engages both the outer, ring gear member  330  and the inner, sun gear member  331  of the planetary gear set  318 . 
         [0080]    The input member  14  is driveably connected to the ring gear  322  of the planetary gear set  316  thereby mechanically locking the rotation of the input member  14  and ring gear  316 . The sun gear  324  of planetary gear set  316  is continuously connected to the rotor  368  of motor/generator  350 . The carrier  326  of planetary gear set  316  is continuously connected to the carrier  332  of planetary gear set  328 , both carriers  326  and  332  are also continuously driveably connected to the output member  62  of the EVT. The sun gear  331  of planetary gear set  318  is continuously connected to the rotor  370  of motor/generator  352 . 
         [0081]    A first torque transfer device  364 , such as a clutch, selectively connects the rotor  368  of motor/generator  350  to the ring gear  330  of the planetary gear set  318 . A second torque transfer device, such as brake  360 , selectively connects the ring gear  330  of the planetary gear set  318  with the ground  358 , such as the transmission housing. That is, the ring gear  330  is selectively secured against rotation by an operative connection to the non-rotatable ground  358 . The carrier  332  of planetary gear set  318  is continuously connected to the output member  62 . 
         [0082]    A control unit  386  regulates the motor speed and torque of motor/generators  350  and  352 . Torque transfer devices  312 ,  354 ,  360  and  364  are selectively controlled by control unit  386  to configure the EVT into various operation modes. The control unit  386  is electrically interfaced to the electrical energy storage device such as a battery  388 . 
         [0083]    Similar to the earlier discussion of EVT  10  presented in  FIG. 1 , in  FIG. 4  torque transfer devices  360  and  354  together with input brake/torque transfer device  312  are employed to assist in the selection of the engine-off battery-only operational modes of the hybrid EVT transmission  78 , as will be hereinafter more fully explained. 
         [0084]    Similar to the earlier discussion concerning  FIG. 1 , electrically variable transmission  78  is of the two mode input/compound split EVT having an input split low range and a compound split high range. Typically, the input split range is used for electric only propulsion mode (vehicle engine off), however, this results in motor/generator  352  spinning at a high negative speed. In an EVT transmission without the input brake  312  of the present invention, operation at compound split range with the engine  80  at zero speed requires motor/generator  352  to operate as a generator when motor/generator  350  is motoring to propel the vehicle or requiring motor/generator  352  to operate as a motor whenever motor/generator  350  is generating electric power. This interaction between motor/generators  350  and  352  results in poor efficiency and limits the usefulness of the compound split range for electric only operation, as discussed earlier. However, if the input member  14  of EVT  78  is locked or braked as by torque transfer or input brake device  312 , then an additional torque reaction point is added at the EVT input member  14  allowing the torques on motor/generators  350  and  352  to be controlled independently. In this case, motor/generator  352  can supply power additively to motor/generator  350 , eliminating circulating power and improving efficiency. With the presence of the input brake  312 , the compound split range now has high torque capacity as the torques of motors  350  and  352  are additive through gear ratios to the output  62 , through two new modes EV 1  and EV 2  as discussed below. 
         [0085]    The clutch states required to actuate the electric drive only EVT transmission modes enabled together with the use of input brake  312  will now be discussed. As discussed earlier, the addition of the input brake  312  to the two mode input/compound split EVT  78  provides additional electric only propulsion, engine off, fixed gear ratio modes of operation of the hybrid vehicle EVT  78 . Two of the possible electric only propulsion EVT fixed gear ration modes are presented herein, the first is the “EV low” (EV 1 ) mode, and the second is the “EV high” (EV 2 ) mode. Referring again to  FIG. 4 , both modes EV 1  and EV 2  require the engine  80  to be in an off state with the torque transfer device or input brake  312  to be engaged, thereby grounding the input member  14  to prevent the rotation of input member  14 . As discussed earlier, this provides another torque reaction point to the EVT  78  and, in particular, locks or inhibits the rotation of either the ring gear  322 . This enforces a fixed gearing ratio between the rotor  368  of motor/generator  350  and the output member  62  through the planetary gear set  316 . 
         [0086]    To enable the “EV low” (EV 1 ) electric only propulsion EVT fixed gear ratio mode, the following torque transfer devices are engaged or locked: brake  360  and torque transmission device/input brake  312 . The remaining clutch  364  is disengaged. Brake  360  locks the ring gear  330  of planetary gear set  318  to ground  358 , thereby enforcing a fixed gear ratio between the rotor  370  of motor/generator  352  and the EVT output member  62  through carrier  332  of planetary gear set  318 . As discussed above, with input brake  312  engaged a fixed gear ratio is also enforced between the rotor  368  of motor/generator  350  and the output member  62  through the planetary gear set  316 . Therefore, both motor/generators  350  and  352  are configured to drive in parallel the output member  62  at fixed gear ratios when in the “EV low” (EV 1 ) mode. 
         [0087]    To enable the “EV high” (EV 2 ) electric only propulsion EVT fixed gear ratio mode, the following clutches and brakes are engaged or locked: clutch  364  and torque transmission device/input brake  312 . The remaining torque transfer device  360  is disengaged. Clutch  364  locks the rotation of the rotor  368  of motor/generator  350  to the ring gear  330  of planetary gear set  318 . As described before in discussions of EV 1  mode, with the input brake  312  engaged a fixed gear ratio is also enforced between the rotor  368  of motor/generator  350  and the output member  62  through the planetary gear set  316 . Motor/generator  352  is driveably connected to output member  62  through the carrier  332  of planetary gear set  318 . The gearing ratio at which the rotor  370  of motor/generator  352  drives the output member  62  is a function of the rotary speed of the rotor  368  of motor/generator  350  as well as the gear ratios between the ring gear  330 , planetary gears  334  and sun gear  331  of planetary gear set  318 . 
         [0088]    As discussed earlier with  FIG. 1 , electric drive only EVT transmission modes EV 1  and EV 2  permit both motor/generators  350  and  352  to be operated in motoring mode to produce mechanical power which is additively combined or electric propulsion, maximizing the designed motor capacity for electric propulsion. Similarly, modes EV 1  and EV 2  enable motor/generators  350  and  352  to operate with additive generating power to maximize utilization of the designed motor capacity for regenerative braking. These fixed gear additive modes are enabled through the addition of the input brake device  312  which locks the input member  14  to facilitate these modes as described above. The addition of the torque transmission device or input brake  312  of the present invention eliminates circulating power and improves operating and energy efficiency of the EVT  78  in electric only modes (engine off) as described above. 
         [0089]    The electric drive only EVT transmission modes are particularly beneficial for use in “plug-in hybrid” applications, that is, a hybrid vehicle that operates in a battery charge depleting mode during a drive schedule, with the battery charge at least partially received from an external off-vehicle power source. One example is a hybrid vehicle configured to receive a substantial electrical charge overnight by plugging or connecting a power cord of the vehicle into an electrical receptacle receiving power from an electric utility. The EVT transmission modes, enabled at least partially through the input brake/torque transfer device  312 , extend vehicle range on battery only engine off operation by improving the electrical energy efficiency of the EVT as discussed earlier. 
         [0090]    In all  FIGS. 1 through 4 , the input torque transfer device/input brake ( 12 ,  112 ,  212 , and  312 ) can include a one way clutch device ( 66 ,  166 ,  266 , and  366 ). The one way clutch ( 66 ,  166 ,  266 , and  366 ) is operable to allow the input member  14  to rotate freely as long as the rotation is in a positive (normal engine operation) direction, i.e. the direction at which a normally operating engine  80  drives the input member  14 . The one way clutch ( 66 ,  166 ,  266 , and  366 ) is operable to prevent the input member  14  from rotating in a negative direction (opposite to the direction of normal engine operation) by engaging and locking the input member  14  to ground ( 58 ,  158 ,  258 , and  358 ). 
         [0091]    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.