Abstract:
Provided for a vehicle is an electrically variable hybrid transmission and powertrain utilizing a flywheel for energy storage. The flywheel is connected to an output shaft of the transmission and a first electric power unit through two planetary gear sets. Also provided is a second electrical power unit selectively coupled to an input shaft of the transmission and continuously coupled to an output shaft of a mechanical power source. The transmission, first and second electrical power units, flywheel, and mechanical power source cooperate to provide a continuously variable rotational speed to a final drive to propel the hybrid powertrain equipped vehicle.

Description:
TECHNICAL FIELD 
     This invention relates to hybrid vehicular powertrains. 
     BACKGROUND OF THE INVENTION 
     The electrically variable hybrid transmission (EVT) system has been proposed for vehicles to improve fuel economy and reduce emissions. The EVT system splits mechanical power between an input shaft and an output shaft of a transmission into a mechanical power path and an electrical power path by differential gearing. The mechanical power path may include torque transmitting mechanisms, such as clutches and brakes, and gears. The electrical power path may employ two electrical power units, each of which may operate as a motor or as a generator. With an energy storage device such as a chemical battery, the EVT system can be incorporated into a hybrid vehicular powertrain for hybrid vehicles. Additional energy storage devices may be incorporated such as flywheel batteries, which use the inertia of a rotating flywheel to store kinetic energy. The kinetic energy is subsequently transformed into electrical energy by employing the rotating flywheel to operate a generator. Traditionally, the flywheel battery is remotely mounted from the EVT system. 
     SUMMARY OF THE INVENTION 
     An electrically variable powertrain is provided including a transmission having an output shaft and a first planetary gear set having first, second, and third members. The second member of the first planetary gear set is continuously interconnected with the output shaft. Also provided is a first electrical power unit, which may be a motor/generator unit, continuously connected with the first member of the first planetary gear set. Additionally, a second planetary gear set having first, second, and third members with the second member being continuously interconnected with the third member of the first planetary gear set. A flywheel is continuously interconnected with the first member of the second planetary gear set, and disposed in concentric relation to the output shaft. 
     The third member of the second planetary gear set may be locked or grounded. The transmission of the present invention may be an automatically shiftable power transmission. The electrically variable powertrain of the present invention may also include a mechanical power source having an output shaft and operable to supply mechanical power to the output shaft. An input shaft connected with the transmission may be provided. The input shaft is selectively rotatably connectable to the output shaft of the mechanical power source. Additionally, a second electrical power unit, which may be a motor/generator unit, may be provided that is continuously connected with respect to the output shaft of the mechanical power source for unitary rotation therewith. An electronic control unit may be provided in electrical communication with the first and second electrical power units. A hydrodynamic drive device may be disposed between, and operable to selectively couple the output shaft of the mechanical power source and the input shaft of the transmission. The hydrodynamic drive device may be a torque converter having a pump section continuously connected with the output shaft of the mechanical power source, a stator, and a turbine section continuously connected with the input shaft of the transmission. A lock up clutch disposed between the output shaft of the mechanical power source and the input shaft of the transmission may be provided. 
     Another aspect of the present invention provides an electrically variable hybrid transmission system including an automatically shiftable power transmission having an input shaft and an output shaft. Also provided is a rotatable flywheel disposed in concentric relation with respect to the output shaft and at least one electrical power unit. Additionally, a first planetary gear set having a first, second, and third member is provided. The first member is continuously interconnected with a first of the at least one electrical power unit and the second member is continuously interconnected with the output shaft of the automatically shifting power transmission. A second planetary gear set having a first, second, and third member is provided. The first member is continuously interconnected with the flywheel, the second member is continuously interconnected with the third member of the first planetary gear set, and the third member is locked or grounded. 
     At least one other electrical power unit may be provided selectively coupled to the input shaft of the automatically shiftable power transmission for substantially unitary rotation therewith. A hydrodynamic drive device may be provided that is operable to selectively couple the other electrical power unit to the input shaft of the automatically shiftable power transmission. 
     Yet another aspect of the present invention provides an electrically variable hybrid transmission system including an automatically shiftable power transmission having an input shaft and an output shaft. A rotatable flywheel disposed in concentric relation with respect to the output shaft is provided. Additionally, first and second electrical power units are provided with an electronic control unit in electrical communication with the first and second electrical power units. The second electrical power unit is selectively coupled to the input shaft of the automatically shiftable power transmission for substantially unitary rotation therewith by a hydrodynamic drive device. The electrically variable hybrid transmission system of the present invention also includes a first planetary gear set having a first, second and third member. The first member is continuously interconnected with the first electrical power unit and the second member is continuously interconnected with the output shaft of the automatically shiftable power transmission. Also provided is a second planetary gear set having a first, second, and third member. The first member is continuously interconnected with the flywheel, the second member is continuously interconnected with the third member of the first planetary gear set, and the third member is locked or grounded. 
     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 electrically variable hybrid powertrain illustrating the aspects of the present invention; and 
         FIG. 2  is a graphical representation illustrating the rotational speeds of various components within the electrically variable powertrain of  FIG. 1  versus the speed of the hybrid vehicle. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to the drawings, there is seen in  FIG. 1  an electrically variable hybrid powertrain  10  incorporating an engine  12 , an electrically variable hybrid transmission system  14 , and a final drive  16 . 
     The electrically variable hybrid transmission system  14  includes an automatically shiftable transmission  18 , a hydrodynamic drive device  20 , a pair of electrical power units  22  and  24 , a main pump  26 , a first planetary gear set  28 , a second planetary gear set  30 , and a flywheel  32 . The hydrodynamic drive device  20  includes a fluid coupling such as a torque converter  34 , and a lock up clutch  36 . The lock up clutch  36  is provided to boost the efficiency of the hydrodynamic drive device  20  by reducing the slip losses within the torque converter  34 . The lock up clutch  36  is preferably an electronically controlled compliance clutch, or ECCC. The ECCC allows a small amount of slip to occur across the lock up clutch  36  to decouple the firing pulses of the engine  12  from the rest of the electrically variable hybrid powertrain  10 . One such system is disclosed in U.S. Pat. No. 4,582,185 to Grimes et al., issued Apr. 15, 1986 and assigned to the assignee of the present invention, which is hereby incorporated by reference in its entirety. The torque converter  34  has a pump section  38 , a stator section  40 , and a turbine section  42 . An output shaft  44  of the engine  12  is continuously connected to the pump section  38 , the electrical power unit  22 , and the main pump  26  for unitary rotation therewith. An input shaft  46  of the automatic transmission  18  is continuously connected to the turbine section  42  of the toque converter  34 . 
     As the engine  12  drives the output shaft  44 , the pump section  38  of the toque converter  34  will force fluid into the turbine section  42  thereby causing rotation of the turbine section  42  and the input shaft  46  connected therewith. The stator  40  provides torque multiplication by directing fluid from the turbine section  42  into the pump section  38 . The engine  12  is preferably an internal combustion engine, such as a spark ignited or compression ignited engine. The lock up clutch  36  is engaged to couple the output shaft  44  of the engine  12  with the input shaft  46  of the transmission  18  for substantially unitary rotation when the relative rotational speed between the pump section  38  and the turbine section  42  are substantially similar. The main pump  26  is operable to provide pressurized fluid to effect engagement of torque transmitting mechanisms (not shown) contained within the automatic transmission  18 . Additionally, the main pump  26  provides lubrication to the automatic transmission  18 . 
     The automatic transmission  18  has a plurality of selectively establishable gear ratios between the engine  12  and the final drive  16 . These ratios are generally established by hydraulically operated torque transmitting mechanisms (not shown), such as clutches and brakes. The engagement and disengagement of these torque transmitting mechanisms are controlled by valve mechanisms (not shown) which direct hydraulic fluid to and from the operating piston of the devices. An output shaft  48  of the automatic transmission  18  is operable to provide drive torque to the final drive  16 . 
     An electronic control unit  50  provides control to the electrical power units  22  and  24 . The electronic control unit  50  is in electrical communication with the electrical power unit  22  through a pair of electrical conductors  52  and  54  and is in electrical communication with the electrical power unit  24  through a pair of electrical conductors  56  and  58 . The electrical power units  22  and  24  are preferably motor/generator units, which can operate as either a power supplier (motor) or a power generator. When either is operating as a motor or power supplier, the electrical power units  22  and  24  will supply power to the automatic transmission  18 . When either is operating as a generator, the electrical power units  22  and  24  will take electrical power from the automatic transmission  18 . The electronic control unit  50  receives a number of inputs from the vehicle, the engine  12 , and the automatic transmission  18 . These inputs may include engine speed, vehicle speed, and intake manifold air pressure to name a few. These inputs are used as input signals for a programmable-type digital computer, which is incorporated within the electronic control unit  50 . The electronic control unit  50  is then effective to distribute control signals to allow the electrically variable hybrid transmission system  14  to operate in a controlled manner. 
     The planetary gear set  28  includes a sun gear member  60 , a ring gear member  62 , and a planet carrier assembly member  64 . The planet carrier assembly member  64  includes a plurality of pinion gear members  66  that are rotatably mounted on a planet carrier  68  and disposed in meshing relationship with both the sun gear member  60  and the ring gear member  62 . 
     The planetary gear set  30  includes a sun gear member  70 , a ring gear member  72 , and a planet carrier assembly member  74 . The planet carrier assembly member  74  includes a plurality of pinion gear members  76  that are rotatably mounted on a planet carrier  78  and disposed in meshing relationship with both the sun gear member  70  and the ring gear member  72 . 
     The electrical power unit  24  is operatively connected to the sun gear member  60  for unitary rotation therewith. The planet carrier  68  is operatively connected to the output shaft  48  for unitary rotation therewith. The ring gear  62  is operatively connected to the planet carrier  78  for unitary rotation therewith. The sun gear  70  is operatively connected to the flywheel  32  for unitary rotation therewith. The ring gear  72  is grounded or held stationary. It should be noted that, where used in the claims, first, second, and third members of the planetary gear sets do not necessarily refer to a member of a particular type; thus, for example, a first member might be any one of a ring gear member, a sun gear member, or a planet carrier. Similarly, as used in the claims, the respective first, second, or third members of two or more gear sets may or may not be the same type of member. 
       FIG. 2  is a graphical depiction of the rotational speed (RPM) of components within the electrically variable powertrain  10  versus the vehicle speed (MPH) of the hybrid vehicle. Referring now to  FIGS. 1 and 2 , the rotational speed of the engine  12  and consequently the rotational speed of electrical power unit  22  is depicted by curve  80 , the rotational speed of the flywheel  32  is depicted by curve  82 , the rotational speed of the electrical power unit  24  is depicted by curve  84 , and the rotational speed of the output shaft  48  of the automatic transmission  18  is depicted by curve  86 . The rotational direction of the engine  12  will be considered forward or positive, while the rotational direction opposite the engine  12  will be considered reverse or negative. The curves shown in  FIG. 2  are for maximum power flow through the vehicle. That is, the engine  12  is operated at its maximum load condition and each of the electrical power units  22  and  24  is operating at its maximum electrical generation and/or power output conditions. 
     When operating the vehicle in reverse, i.e. negative vehicle speeds, the speed of the engine  12  and the electrical power unit  22  increases from an idle point as shown by curve  80 . In the reverse mode, the output shaft  48  will rotate in a negative direction and will cause the vehicle to move in reverse. The electrical power unit  24  will operate as a generator providing electrical power to the electrical power unit  22 , which is operating as a motor. 
     When operating the vehicle in the forward range mode of operation, the rotational speed of the engine  12  and the electrical power unit  22  will increase from an idle speed condition as illustrated by curve  80 . The step like nature of the curve  80  is a result of the lock-up clutch  36  engaging at different gear ratios of the automatic transmission  18 . The rotational speed of the output shaft  48  will increase, as illustrated by curve  86 , propelling the vehicle forward. The rotational speed of the flywheel  32  will decrease, as illustrated by curve  82 , transferring the kinetic energy of rotation to the electrical power unit  24  through the planetary gear sets  28  and  30 . The electrical power unit  24 , operating as a generator provides electrical power to the electrical power unit  22 , which is operating as a motor, via the electronic control unit  50 . When operating the vehicle at speeds represented by point  88 , shown in  FIG. 2 , the electrical power unit  24  switches from operating as a generator and begins operating as a generator. Concurrently, the electrical power unit  22  switches from operating as a motor to operating as a generator. The flywheel  32  will continue to provide power to the electrically variable powertrain  10  until point  90 , shown in  FIG. 2 . At point  90 , the electrical power units  22  and  24  operate as generators. 
     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.