Patent Publication Number: US-11639094-B2

Title: Distributed drivetrain architectures for commercial vehicles with a hybrid electric powertrain and dual range disconnect axles

Description:
CLAIM OF PRIORITY 
     The present application is a continuation of U.S. patent application Ser. No. 15/781,807, entitled “DISTRIBUTED DRIVETRAIN ARCHITECTURES FOR COMMERCIAL VEHICLES WITH A HYBRID ELECTRIC POWERTRAIN AND DUAL RANGE DISCONNECT AXLES,” and filed on Jun. 6, 2018. U.S. patent application Ser. No. 15/781,807 is a national phase of International Patent Application No. PCT/US2016/065285, filed on Dec. 7, 2016. International Patent Application No. PCT/US2016/065285 claims priority to U.S. Provisional Patent Application No. 62/406,126, filed on Oct. 10, 2016, and U.S. Provisional Patent Application No. 62/264,089, filed on Dec. 7, 2015. The entire contents of the above-listed applications are hereby incorporated by reference for all purposes. 
    
    
     FIELD OF THE INVENTION 
     The present application relates to drivetrains for commercial vehicles and more particularly to hybrid electric drivetrains for commercial vehicles. 
     BACKGROUND OF THE INVENTION 
     Commercial vehicles or trailers having two or more rear axles allow such vehicles to carry greater loads when compared to vehicles and trailers having a single axle. Further, tractive effort and load distribution can be increased in these vehicles. 
     Hybrid powertrains incorporate a second power source, such as a motor-generator and a battery, that can be used to increase an efficiency of a drivetrain. Currently, few options for hybridized drivetrains for commercial vehicles are available. Because of the unique demands of commercial vehicles, such as the need for a low speed, high torque mode of operation while also having a high speed, low torque mode of operation, many challenges exist in successfully implementing a hybridized drivetrain for use with commercial vehicles. Further, regulations posed by governments increasingly demand fuel efficiency improvements for such vehicles. 
     It would be advantageous to develop a hybridized drivetrain for commercial vehicles that meets the exacting needs of commercial vehicles while providing fuel efficiency improvements for vehicles incorporating the hybridized drivetrain. 
     SUMMARY OF THE INVENTION 
     Presently provided by the application, a hybridized drivetrain for commercial vehicles that meets the exacting needs of commercial vehicles while providing fuel efficiency improvements for vehicles incorporating the hybridized drivetrain, has surprisingly been discovered. 
     In one embodiment, the present application is directed to a hybrid drivetrain. The hybrid drivetrain comprises a power source, a transmission, and a tandem axle assembly. The transmission includes a primary clutch and is drivingly engaged with the power source. The tandem axle assembly includes a first axle and a second axle and is drivingly engaged with the transmission. One of the transmission and the tandem axle assembly includes a first motor generator in electrical communication with a battery. The first motor generator and the primary clutch facilitate operating the hybrid drivetrain as a hybrid drivetrain in a plurality of operating modes. 
     It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure. 
     Various aspects of this application will become apparent to those skilled in the art from the following detailed description of the described embodiments, when read in light of the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above, as well as other advantages of the present application, will become readily apparent to those skilled in the art from the following detailed description when considered in the light of the accompanying drawings in which: 
         FIG.  1    is a schematic style view of a hybrid drivetrain according to a first embodiment of the application; 
         FIG.  2    is a schematic style view of a hybrid drivetrain according to another embodiment of the application; 
         FIG.  3    is a schematic style view of a hybrid drivetrain according to another embodiment of the application; 
         FIG.  4    is a schematic style view of a hybrid drivetrain according to another embodiment of the application; 
         FIG.  5    is a schematic style view of a hybrid drivetrain according to another embodiment of the application; 
         FIG.  6    is a schematic style view of a hybrid drivetrain according to another embodiment of the application; 
         FIG.  7    is a schematic style view of a hybrid drivetrain according to another embodiment of the application; 
         FIG.  8    is a schematic style view of a hybrid drivetrain according to another embodiment of the application; 
         FIG.  9    is a schematic style view of a hybrid drivetrain according to another embodiment of the application; and 
         FIG.  10    is a schematic style view of a hybrid drivetrain according to another embodiment of the application. 
     
    
    
     DETAILED DESCRIPTION 
     It is to be understood that the application may assume various alternative orientations and step sequences, except where expressly specified to the contrary. It is also to be understood that the specific devices and processes illustrated in the attached drawings, and described in the following specification are simply exemplary embodiments of the inventive concepts of the present application. Hence, specific dimensions, directions, orientations or other physical characteristics relating to the embodiments disclosed are not to be considered as limiting, unless expressly stated otherwise. 
       FIG.  1    is a schematic style view of a hybrid drivetrain  100  according to a first embodiment of the application. The hybrid drivetrain  100  includes a power source  102 , a hybrid transmission  104 , and a tandem axle drive unit  106 , the tandem drive axle unit  106  including a first axle drive unit  144  and a second axle drive unit  146 . The power source  102  is drivingly engaged with an input of the hybrid transmission  104 . The tandem axle drive unit  106  is drivingly engaged with an output of the hybrid transmission  104 . 
     The power source  102  is an internal combustion engine, however, it is understood that the power source  102  may also be a hybrid type power source incorporating a secondary power source in addition to an internal combustion engine. Further, it is understood that the power source  102  may also be a source of electrical power, such as a fuel cell. The hybrid transmission  104  includes a primary clutch  108 , a planetary gearset  110 , a first motor-generator  112 , a second motor-generator  114 , a secondary clutch  116 , and a gear box  118 . A portion of the primary clutch  108  acts as the input for the hybrid transmission  104 . A portion of the gear box  118  acts as the output for the hybrid transmission  104 . The primary clutch  108 , the first motor-generator  112 , and second motor-generator  114  are in driving engagement with portions of the planetary gearset  110 . The secondary clutch  116  is in driving engagement with the first motor-generator  112  and the gear box  118 . 
     The primary clutch  108  is a clutch which can be variably engaged, such as a plate or cone style clutch. 
     The planetary gearset  110  comprises a sun gear portion  120 , a carrier portion  122 , and a ring gear portion  124 . The sun gear portion  120  is in driving engagement with the second motor-generator  114 . The carrier portion  122  is in driving engagement with a portion of the primary clutch  108 . The ring gear portion  24  is in driving engagement with the first motor-generator  112 . It is understood that the planetary gearset  110  may have other configurations that facilitate a similar operation; in which torques applied by the power source  102  and the second motor generator  114  may be summed and applied to the first motor generator  112 . 
     The first motor generator  112  is in driving engagement with the ring gear portion  124  of the planetary gearset  110  and the secondary clutch  116 . The first motor generator  112  is in electrical communication with a controller  126  and a battery  128 . It is understood that the first motor generator  112 , or any of the other motor generators described herein, may be incorporated into a gearbox, transmission, or other driveline component of the hybrid drivetrain  100 . Depending on an electrical control of the first motor generator  112  using the controller  126 , the first motor generator  112  may apply a driving force to propel or retard a portion of the hybrid drivetrain  100  it is drivingly engaged with. 
     The second motor generator  114  is in driving engagement with the sun gear portion  120  of the planetary gearset  110  and the secondary clutch  116 . The second motor generator  1   4  is in electrical communication with the controller  126  and the battery  128 . It is understood that the second motor generator  114 , or any of the other motor generators described herein, may be incorporated into a gearbox, transmission, or other driveline component of the hybrid drivetrain  100 . Depending on an electrical control of the second motor generator  114  using the controller  126 , the first motor generator  112  may apply a driving force to propel or retard a portion of the hybrid drivetrain  100  it is drivingly engaged with. 
     The secondary clutch  116  is a clutch which can be variably engaged, such as a plate or cone style clutch. 
     The gear box  118  is a multi-speed gearbox in driving engagement with the secondary clutch  116  and the tandem axle drive unit  106 . The gear box  18  may be manually or automatically operated. 
     The tandem axle drive unit  06  is drivingly engaged with the gear box  118 , a first axle  130 , and a second axle  132 . The tandem axle drive unit  106  is configured to be placed in two modes of operation, depending on a position of a selection clutch  134 . In a first mode of operation, the tandem axle drive unit  106  operates in a high torque, dual axle mode operation. In a second mode of operation, the tandem axle drive unit  106  operates in a low torque, single axle mode operation. As shown in  FIG.  1   , the hybrid driveline  100  includes an optional axle disconnect clutch  136 . The tandem axle drive unit  106  is similar in structure and functionality to the planetary drive unit  716  shown in  FIG.  7   , described hereinbelow. 
     In use, through control of the primary clutch  108  and the secondary clutch  116 , driving and charging can occur with and without engagement with the rest of the hybrid drivetrain  100 . The hybrid drivetrain  100  is a series-parallel hybrid drivetrain, and may be operated in a plurality of operating modes as described hereinbelow. The first motor generator  112  is placed inline in the hybrid drivetrain  100 , and the second motor generator  114  can be used to supplement the hybrid drivetrain  100  through the planetary gearset  110 . The motor generators  12 ,  114  provide the following benefits: engine downsizing, efficiency improvement by operating the power source  102  within a narrower band (allowing the second motor generator  114  to provide acceleration flexibility), reduced gearing in the gearbox  118 , and a downsizing of the axles  130 ,  132 . 
       FIG.  2    is a schematic style view of a hybrid drivetrain  200  according to another embodiment of the application. The hybrid drivetrain  200  includes a power source  202 , a hybrid transmission  204 , and a tandem axle drive unit  206 , the tandem axle drive unit  206  including a first axle drive unit  244  and a second axle drive unit  246 . The power source  202  is drivingly engaged with an input of the hybrid transmission  204 . The tandem axle drive unit  206  is drivingly engaged with an output of the hybrid transmission  204 . The hybrid drivetrain  200  is similar to the hybrid drivetrain  100  shown in  FIG.  1   , with the exception that the hybrid drivetrain  200  shown in  FIG.  2    does not include the primary clutch  108 . The clutch  216  facilitates disengaging the gear box  218  from the first motor generator  212 . 
       FIG.  3    is a schematic style view of a hybrid drivetrain  300  according to another embodiment of the application. The hybrid drivetrain  300  includes a power source  302 , a hybrid transmission  304 , and a tandem axle drive unit  306 , the tandem axle drive unit  306  including a first axle drive unit  344  and a second axle drive unit  346 . The power source  302  is drivingly engaged with an input of the hybrid transmission  304 . The tandem axle drive unit  306  is drivingly engaged with an output of the hybrid transmission  304 . The hybrid drivetrain  300  is similar to the hybrid drivetrain  100  shown in  FIG.  1   , with the exception that the hybrid drivetrain  300  shown in  FIG.  3    does not include the secondary clutch  116 . 
       FIG.  4    is a schematic style view of a hybrid drivetrain  400  according to another embodiment of the application. The hybrid drivetrain  400  includes a power source  402 , a hybrid transmission  404 , and a motorized tandem axle drive unit  438 , the motorized tandem axle drive unit  438  including a first axle drive unit  444  and a second axle drive unit  446 . The power source  402  is drivingly engaged with an input of the hybrid transmission  404 . The motorized tandem axle drive unit  438  is drivingly engaged with an output of the hybrid transmission  404 . The hybrid drivetrain is similar to the hybrid drivetrain  100  shown in  FIG.  1   , with the exception that the hybrid drivetrain shown in  FIG.  4    does not include the secondary clutch  116  and includes the motorized tandem axle drive unit  438 . 
     The motorized tandem axle drive unit  438  is drivingly engaged with a gear box  418 , a first axle  430 , and a second axle  432 . Unlike the tandem axle drive unit  106  shown in  FIG.  1   , the motorized tandem axle drive unit  438  includes a third motor generator  440  in driving engagement therewith. Further, it is understood that the third motor generator  440 , or any other motor generator described herein, may include a power inverter  442 , integrated therewith to facilitate a conversion of electrical power needed to operate the third motor generator  440 . The third motor generator  440  is in electrical communication with the controller  426  and the battery  428 . It is understood that the third motor generator  440 , or any of the other motor generators described herein, may be incorporated into a gearbox, transmission, or other driveline component of the hybrid drivetrain  400 . The motorized tandem axle drive unit  438  is configured to be placed in two modes of operation, depending on a position of a selection clutch  434 . In a first mode of operation, the motorized tandem axle drive unit  438  operates in a high torque, dual axle mode operation, and the third motor generator  440  may apply a driving force to propel or retard a portion of the hybrid drivetrain  400  it is drivingly engaged with. In a second mode of operation, the motorized tandem axle drive unit  438  operates in a low torque, single axle mode operation. 
       FIG.  5    is a schematic style view of a hybrid drivetrain  500  according to another embodiment of the application. The hybrid drivetrain includes a power source  502 , a hybrid transmission  504 , and a tandem axle unit  506 , the tandem axle unit  506  including a first axle drive unit  544  and a second axle drive unit  546 . The power source  502  is drivingly engaged with an input of the hybrid transmission  504 . The first axle drive unit  544  is drivingly engaged with an output of the hybrid transmission  504 . The second axle drive unit  546  is in electrical communication with a controller  526  and a battery  528  of the hybrid drivetrain  500 . The hybrid drivetrain  500  is similar to the hybrid drivetrain  100  shown in  FIG.  1   , with the exception that the hybrid drivetrain shown in  FIG.  5    includes the first axle drive unit  544  and the second axle drive unit  546 . 
     The first axle drive unit  544  is drivingly engaged with a gear box  518  and a first axle  530  of the hybrid drivetrain  500 . The first axle drive unit  544  is conventional and well known in the art and comprises a drive pinion, a ring gear, and differential assembly. 
     The second axle drive unit  546  includes a third motor generator  548  and is drivingly engaged with a second axle  532  of the hybrid drivetrain. The third motor generator  548  is in electrical communication with the controller  526  and the battery  528 . It is understood that the third motor generator  548 , or any of the other motor generators described herein, may be incorporated into a gearbox, transmission, or other driveline component of the hybrid drivetrain  500 . The third motor generator  548  may apply a driving force to propel or retard the second axle drive unit  546  of the hybrid drivetrain  500  through a countershaft gear assembly  550  and second axle  532 , for example. Further, it is understood that the third motor generator  548 , or any other motor generator described herein, may include a power inverter  552 , integrated therewith to facilitate a conversion of electrical power needed to operate the third motor generator  548 . 
       FIG.  6    is a schematic style view of a hybrid drivetrain  600  according to another embodiment of the application. The hybrid drivetrain  600  includes a power source  602 , a hybrid transmission  604 , and a tandem axle unit  606 , the tandem axle unit  606  including a first axle drive unit  644  and a second axle drive unit  646 . The power source  602  is drivingly engaged with an input of the hybrid transmission  604 . The first axle drive unit  644  is drivingly engaged with an output of the hybrid transmission  604 . 
     The hybrid transmission  604  includes a primary clutch  610 , a first motor-generator  612 , and a gear box  614 . A portion of the primary clutch  610  acts as the input for the hybrid transmission  604 . A portion of the gear box  614  acts as the output for the hybrid transmission  604 . 
     The first motor generator  612  is in driving engagement with the primary clutch  610  and the gear box  614 . The first motor generator  612  is in electrical communication with a controller  616  and a battery  618 . It is understood that the first motor generator  612 , or any of the other motor generators described herein, may be incorporated into a gearbox, transmission, or other driveline component of the hybrid drivetrain  600 . Depending on an electrical control of the first motor generator  612  using the controller  616 , the first motor generator  6   2  may apply a driving force to propel or retard a portion of the hybrid drivetrain  600  it is drivingly engaged with. 
     The first axle drive unit  644  is drivingly engaged with the gear box  614  and a first axle  620  of the hybrid drivetrain  600 . The first axle drive unit  644  is conventional and well known in the art. 
     The second axle drive unit  646  includes a second motor generator  622  and is drivingly engaged with a second axle  624  of the hybrid drivetrain  600 . The second motor generator  622  is in electrical communication with the controller  616  and the battery  618 . It is understood that the second motor generator  622 , or any of the other motor generators described herein, may be incorporated into a gearbox, transmission, or other driveline component of the hybrid drivetrain  600 . The second motor generator  622  may apply force to propel or retard the second axle  624  of the hybrid drivetrain  600 . As shown in  FIG.  6   , the hybrid driveline includes as optional axle disconnect clutch  626 . The hybrid drivetrain  600  is a parallel hybrid drivetrain, and may be operated in a plurality of operating modes as described hereinbelow. The second motor generator  622  may also include additional components to facilitate operation and increased functionality of the second motor generator  622 , such as but not limited to, an inverter  630 , power electronics for control of the second motor generator  622 , a DC-DC converter, or electronics used for a generator function. It is also understood that second motor generator  622  may include at least a portion of a cooling system used for electrical components. 
     In use, the hybrid drivetrain  600  may be operated in a plurality of operating modes. The hybrid drivetrain  600  may be operated in an all-electric mode, a hybrid mode, a regeneration/braking mode, a charging mode, and a direct drive mode. Further, it is understood that the operating modes described hereinbelow with respect to the hybrid drivetrain  600  may be adapted for use with the other hybrid drivetrains described herein, utilizing the architecture of each to operate in the all-electric mode (where applicable), the hybrid mode, the regeneration/braking mode, the charging mode, and the direct drive mode. 
     In one embodiment of the all-electric mode, the primary clutch  610  is placed in a disengaged position, and the battery  618  serves as the only power source for the hybrid drivetrain  600  for the vehicle. In the all-electric mode, the hybrid transmission  604 , the second motor generator  622 , or both the hybrid transmission  604  and second motor generator  622  may apply force to the hybrid drivetrain  600 , causing rotation of at least one of a plurality of wheel assemblies  628 , propelling the vehicle. When only the hybrid transmission  604  is used in the all-electric mode, the axle disconnect clutch  626  may be placed in a disengaged position, and the first motor-generator  612  of the hybrid transmission  604 , in response to communication with the controller  616 , applies force to the hybrid drivetrain  600  to propel the vehicle. When only the second motor generator  622  is used in the all-electric mode, the primary clutch  610  is placed in a disengaged position, and the second motor generator  622 , in response to communication with the controller  616 , applies a driving force to propel the hybrid drivetrain  600  through the second axle  624 . When both the hybrid transmission  604  and the second motor generator  622  are used in the all-electric mode, the primary clutch  610  and the axle disconnect clutch  626  are \ placed in an engaged position and the hybrid transmission  604  and the second motor generator  622 , in response to communication with the controller  616 , apply force to the hybrid drivetrain  600  to propel the vehicle. 
     In the hybrid mode, the primary clutch  610  is placed in an engaged position, and the battery  618  and the power source  602  serve as a combined power source for the hybrid drivetrain  600  for the vehicle. In the hybrid mode, the hybrid transmission  604 , the second motor generator  622 , or both the hybrid transmission  604  and the second motor generator  622 , in addition to the power source  602 , may apply a driving force to the hybrid drivetrain  600  to propel the vehicle. When the hybrid transmission  604  and the second motor generator  622  are used in the hybrid mode, the primary clutch  610  and the axle disconnect clutch  626  are placed in an engaged position, and the hybrid transmission  604 , the second motor generator  622 , and the power source  602 , in response to communication with the controller  616 , apply force to the hybrid drivetrain  600  to propel the vehicle. When the hybrid transmission  604  is used in the hybrid mode, the primary clutch  6   0  is placed in an engaged position and the axle disconnect clutch  626  is placed in a disengaged position, and the hybrid transmission  604  and the power source  602  (applying a driving force through the first motor generator  612 ), in response to communication with the controller  616 , apply a driving force to the hybrid drivetrain  600  to propel the vehicle. When the second motor generator  622  is used in the hybrid mode, the primary clutch  610  and the axle disconnect clutch  626  are placed in an engaged position, and the second motor generator  622  and the power source  602  (applying force through the first motor generator  6   2 ), in response to communication with the controller  616 , apply a driving force to the hybrid drivetrain  600  to propel the vehicle. 
     In the regeneration/braking mode, the hybrid transmission  604 , the second motor generator  622 , or both the hybrid transmission  604  and the second motor generator  622  are used to retard the hybrid drivetrain  600  for the vehicle to facilitate capturing kinetic energy of the vehicle as electrical power to be stored in the battery  618 . The regeneration/braking mode may be used to assist a conventional braking system or may be used to regulate a speed of the vehicle when descending an incline. When the second motor generator  622  is used in the regeneration/braking mode, the axle disconnect clutch  626  is placed in an engaged position and the primary clutch  610  may be placed in a disengaged condition (it is understood that engine braking using the power source  602  may or may not be used in addition to the regeneration/braking mode), and the second motor generator  622  retards the hybrid drivetrain  600  to capture kinetic energy as electrical power. When the hybrid transmission  604  is used in the regeneration/braking mode, the axle disconnect clutch  626  may be placed in a disengaged position and the primary clutch  610  may be placed in a disengaged condition (it is understood that engine braking using the power source  602  may or may not be used in addition to the regeneration/braking mode), and the hybrid transmission  604  retards the hybrid drivetrain  600  to capture kinetic energy as electrical power. When both the hybrid transmission  604  and the second motor generator  622  are used in the regeneration/braking mode, the axle disconnect clutch  626  is placed in a disengaged position and the primary clutch  610  may be placed in a disengaged condition (it is understood that engine braking using the power source  602  may or may not be used in addition to the regeneration/braking mode), and both the hybrid transmission  604  and the second motor generator  622  retard the hybrid drivetrain  600  to capture kinetic energy as electrical power. 
     In the charging mode, the power source  602  and the first motor generator  612  or the second motor generator  622  are used to charge the battery  618 . It is understood that the charging mode may be utilized when the hybrid transmission  604  is propelling the vehicle in the direct drive mode. In the charging mode, the axle disconnect clutch  626  may be placed in a disengaged position and the primary clutch  610  is placed in an engaged condition, allowing the power source  602  and the first motor generator  612  to charge the battery  618  while the hybrid transmission  604  is used to propel the vehicle, if desired. 
     In the direct drive mode, neither the first motor generator  612  nor the second motor generator  622  are used to propel the vehicle. It is understood that the direct drive mode may be utilized when a charge level of the battery  618  does not permit operation in the all-electric or hybrid modes. In the direct drive mode, the primary clutch  610  is placed in an engaged position, and the power source  602  in response to communication with the controller  616 , applies force (through the first motor generator  612  and the hybrid transmission  604 ) to the hybrid drivetrain  600  to propel the vehicle. 
       FIG.  7    is a schematic style view of a hybrid drivetrain  700  according to another embodiment of the application. The hybrid drivetrain  700  includes a power source  702 , a transmission  704 , and a hybrid tandem axle drive unit  706 , the hybrid tandem axle drive unit  706  including a first axle drive unit  7   8  and a second axle drive unit  720 . The power source  702  is drivingly engaged with an input of the transmission  704 . The hybrid tandem axle drive unit  706  is drivingly engaged with an output of the transmission  704  through a Cardan shaft  708 , for example. 
     The power source  702  is an internal combustion engine, however, it is understood that the power source  702  may also be a hybrid type power source incorporating a secondary power source in addition to an internal combustion engine. Further, it is understood that the power source  702  may also be a source of electrical power, such as a fuel cell. 
     The transmission  704  includes at least a primary clutch  710  and a gear arrangement  712 ; however, it is understood that the primary clutch  710  may form a portion of the gear arrangement  712  or that the primary clutch  710  is a separate component from the gear arrangement  712  and drivingly engaged there with in any conventional manner. A portion of the primary clutch  710  acts as the input for the transmission  704 . A portion of the gear arrangement  712  acts as the output for the transmission  704 . The primary clutch  710  is a clutch which can be variably engaged, such as a plate or cone style clutch. The gear arrangement  712  forms a multi-speed gearbox in driving engagement with a portion of the primary clutch  710  and the hybrid tandem axle drive unit  706 . The gear arrangement  712  may be manually or automatically operated. 
     The hybrid tandem axle drive unit  706  is drivingly engaged with the transmission  704  through the Cardan shaft  708 ; however, it is understood that certain embodiments of the application may not require the Cardan shaft  708 . The hybrid tandem axle drive unit  706  comprises a motor-generator  714 , a planetary drive unit  716 , a first axle drive assembly  718 , and a second axle drive assembly  720 . The hybrid tandem axle drive unit  706  is configured to be placed in at least two modes of operation, depending on a position of a selection clutch  722  of the planetary drive unit  716 . In a first mode of operation, the hybrid tandem axle drive unit  706  operates in a high torque, dual axle mode operation. In a second mode of operation, the hybrid tandem axle drive unit  706  operates in a low torque, single axle mode operation. As shown in  FIG.  7   , the hybrid driveline  700  includes as optional an axle disconnect clutch  724  forming a portion of the second axle drive assembly  720 . 
     The motor-generator  714  is in driving engagement with the transmission  704  through the Cardan shaft  708  and the planetary drive unit  716 . The motor-generator  714  is in electrical communication with a controller  726  and a battery  728 . It is understood that the third motor-generator  714 , or any of the other motor generators described herein, may be incorporated into a gearbox, transmission, or other driveline component of the hybrid drivetrain  700 . Depending on an electrical control of the motor-generator  714  using the controller  726 , the motor-generator  714  may apply force to or retard the portion of the hybrid drivetrain  700  it is drivingly engaged with. The motor-generator  714  may also include additional components to facilitate operation and increased functionality of the motor-generator  714 , such as but not limited to, an inverter, power electronics for control of the motor-generator  714 , a DC-DC converter, or electronics used for a generator function. It is also understood that the motor-generator  714  may include at least a portion of a cooling system used for electrical components. 
     The controller  726  is in electrical communication with at least the motor-generator  714  and the battery  728 . The controller  726  may be a hybrid supervisory controller with dual range disconnect control management. It is understood that the controller  726  may also be in communication with at least one of the power source  702 , the primary clutch  710 , the planetary drive unit  716 , the axle disconnect clutch  724  of the hybrid tandem axle drive unit  706 , a vehicle controller (not shown), the gear arrangement  712 , an engine controller (not shown), a braking controller (not shown), another type of controller, an advanced driver assistance system (ADAS), or an automated driving controller. The controller  726  controls an operating mode of the hybrid tandem axle drive  706  unit by at least controlling engagement of the primary clutch  710 , by communicating with a transmission controller (not shown) to adjust an operating range of the gear arrangement  712 , by controlling the axle mode, by adjusting a position of the selection clutch  722  of the planetary drive unit  716 , by controlling the motor-generator  714 , and by adjusting a position of the axle disconnect clutch  724  to apply a driving force to propel or retard portions of the hybrid drivetrain  700  each are respectively drivingly engaged with. 
     The battery  728  is a rechargeable, electrochemical energy storage device in electrical communication with the controller  726  and the motor-generator  714 . It is understood that the battery  728  may also be in electrical communication with other components of the hybrid drivetrain  700  or the vehicle to supply power thereto. Further, it is understood that the battery  728  may also be another type of electrical storage, such as an supercapacitor. In response to the controller  726  adjusting an operating mode of the hybrid drivetrain  700 , the battery  728  may be charged or discharged. It is also understood that the battery  728  may include at least a portion of a cooling system used for electrical components. The planetary drive unit  716  includes an input shaft  732 , a plurality of driving pinions  734 , a transfer shaft  736 , a second output gear  738 , a first output gear  740 , and the selection clutch  722 . The components  732 ,  734 ,  736 ,  738 ,  740 ,  722  may be formed from a hardened steel, however the components  732 ,  734 ,  736 ,  738 ,  740 ,  722  may be formed from any other rigid material. As shown, the planetary drive unit  716  includes the six components  732 ,  734 ,  736 ,  738 ,  740 ,  722  disposed in a housing  741  but it is understood the planetary drive unit  716  may include fewer or more components. In response to a signal sent by the controller  726 , an actuator  742  adjusts a position of the selection clutch  722 . 
     The input shaft  732  is at least partially disposed in a housing (not shown). The input shaft  732  may be an elongate member, however the input shaft  732  may be any other shape. Bearings (not shown) disposed between the input shaft  732  and the housing permit the input shaft  732  to rotate about an axis of the input shaft  732 . The input shaft  732  has a first end portion drivingly engaged with the motor-generator  714  and a second end portion having a pinion carrier  746 , a first set of clutch gear teeth  748 , and an engagement portion  750  formed thereon. The second end portion is a substantially hollow body having a diameter greater than a diameter of the first end portion. The second end portion is drivingly coupled to the input shaft  732 . Alternately, the second end portion may be integrally formed with the input shaft  732 . 
     The pinion carrier  746  is a substantially disc shaped body drivingly coupled to the second end portion of the input shaft  732 . The pinion carrier  746  includes a plurality of pinion supports  752  protruding from a first side of the pinion carrier  746  into the second end portion of the input shaft  732 . The engagement portion  750  is formed on a second side of the pinion carrier  746 . As is known in the art, the pinion carrier  746  is also known as a planet carrier. 
     The engagement portion  750  is a conical surface oblique to the input shaft  732 , however, the engagement portion  750  may have any other shape. The first set of clutch gear teeth  748  are formed on the pinion carrier  746  radially inward from the engagement portion  750 . 
     The plurality of driving pinions  734  are rotatably coupled to the pinion supports  752 . Each of the driving pinions  734  have gear teeth formed on an outer surface thereof. As is known in the art, each of the driving pinions  734  is also known as a planet gear. Bearings may be disposed between each of the driving pinions  734  and the pinion supports  752 , however, the driving pinions  710  may be directly mounted on the pinion supports. 
     The transfer shaft  736  is a shaft rotatably disposed in the housing and having an axis of rotation concurrent with the axis of rotation of the input shaft  732 . The transfer shaft  736  may be a hollow elongate cylindrical member, however the transfer shaft  736  may be any other shape. Bearings (not shown) disposed between the transfer shaft  736  and pinion carrier  746  permit the transfer shaft  736  to rotate about an axis of the transfer shaft  736 . The transfer shaft  736  has a first end portion having a first set of clutch gear teeth  754  formed on an outer surface thereof, and a second end portion having a second set of gear teeth  756  formed on an outer surface thereof. The first end portion and the second end portion are integrally formed with the transfer shaft  736  and may have a diameter substantially equal to the transfer shaft  736 . Alternately, the first end portion and the second end portion may be substantially disc shaped bodies having an outer diameter greater than a diameter of the transfer shaft  736 . The first end portion and the second end portion may be drivingly coupled to the transfer shaft  736 . Similarly, the first set of clutch gear teeth  754  and the second set of gear teeth  756  may be formed directly in the transfer shaft  736 . As is known in the art, the second end portion having the gear teeth  756  is known as a sun gear. The second set of gear teeth  756  are engaged with the plurality of driving pinions  734  and the first set of clutch gear teeth  754  are disposed adjacent the first set of clutch gear teeth  748  of the pinion carrier  746 . 
     The second output gear  738  is a gear concentrically disposed about a portion of the transfer shaft  736 . The second output gear  738  has a central perforation having a diameter greater than a diameter of the transfer shaft  736 . The second output gear  738  is a substantially disc shaped body having a first end portion, a second end portion defining an outer diameter of the second output gear  738 , and an engagement portion  758 . Bearings disposed between the second output gear  738  and the housing permit the second output gear  738  to rotate about an axis of the second output gear  738 . The axis of the second output gear  738  is concurrent with the axis of the input shaft  732 . A first set of clutch gear teeth  760  are formed on the first end portion adjacent the first set of clutch gear teeth  754  of the transfer shaft  736 . A second set of gear teeth  762  are formed on the second end portion. The engagement portion  758  is formed in the second output gear  738  intermediate the first end portion and the second end portion. As shown, the engagement portion  758  is a conical surface oblique to the input shaft  732 ; however, the engagement portion  758  may have any other shape. 
     The selection clutch  722  is concentrically disposed about the transfer shaft  736 . The selection clutch  722  includes a set of inner clutch collar teeth  764  formed on an inner surface thereof, a first synchronizer ring  766 , and a second synchronizer ring  768 . The second synchronizer ring  768  may be a cone clutch that is used in conjunction with a dog clutch, wherein shifting the selection clutch  722  utilizes a torque interrupt shift. It is understood that it is also within the scope of the application for the selection clutch  722  to be a dog style clutch that does not utilize synchronizers, requiring the hybrid driveline  700  to be placed in a non-moving state before the selection clutch  722  can be moved. The set of inner clutch collar teeth  764  are engaged with the first set of clutch gear teeth  754  of the transfer shaft  736 . The selection clutch  722  can be slidably moved along the axis of the input shaft  732  as directed by the controller  726  while maintaining engagement of the inner clutch collar teeth  764  and the first set of clutch gear teeth  754 . A shift fork  770  disposed in an annular recess formed in the selection clutch  722  moves the selection clutch  722  along the axis of the input shaft  732  into a first position, a second position, or a neutral position. The actuator  742 , which is drivingly engaged with the shift fork  770 , is engaged to position the shift fork  770  as directed by the controller  726 . Consequently, the shift fork  770  positions the selection clutch  722  into the first position, the second position, or the neutral position. In the first position, the selection clutch  722  is drivingly engaged with the first set of clutch gear teeth  754  of the transfer shaft  736  and the first set of clutch gear teeth  748  of the pinion carrier  746 . In the second position, the selection clutch  722  is drivingly engaged with the first set of clutch gear teeth  754  of the transfer shaft  736  and the first set of clutch gear teeth  760  of the second output gear  738 . In one embodiment of the neutral position, the inner clutch collar teeth  764  of the selection clutch  722  are only drivingly engaged with the first set of clutch gear teeth  754  of the transfer shaft  736 . It is understood the selection clutch  722 , the clutch gear teeth  754 ,  748 ,  760 ,  764 , the synchronizer rings  766 ,  768 , and the engagement portions  750 ,  758  may be substituted with any clutching device that permits selective engagement of a driving and a driven part. 
     The first synchronizer ring  766  is an annular body coupled to the selection clutch  722  adjacent the engagement portion  750  of the pinion carrier  746 . The first synchronizer ring  766  has a first conical engagement surface. Alternately, the first synchronizer ring  766  may have an engagement surface having any other shape. A biasing member (not shown) is disposed between the selection clutch  722  and the first synchronizer ring  766  to urge the first synchronizer ring  766  away from the selection clutch  722 . When the selection clutch  722  is moved from the second position into the first position, the first conical engagement surface contacts the engagement portion  750  of the pinion carrier  746 . As the selection clutch  722  moves towards the first set of clutch gear teeth  748  of the input shaft  732 , the biasing member is compressed while the selection clutch  722  engages the first set of clutch gear teeth  748  of the transfer shaft  736  and before the selection clutch  722  engages the first set of clutch gear teeth  748  of the pinion carrier  746 . 
     The second synchronizer ring  768  is an annular body coupled to the selection clutch  722  adjacent the first end portion of the second output gear  738 . The second synchronizer ring  768  has a second conical engagement surface. Alternately, the second synchronizer ring  738  may have an engagement surface having any other shape. A biasing member (not shown) is disposed between the selection clutch  722  and the second synchronizer ring  768  to urge the second synchronizer ring  768  away from the selection clutch  722 . When the selection clutch  722  is moved from the first position into the second position, the second conical engagement surface contacts the engagement portion  758  of the second output gear  738 . As the selection clutch  722  moves towards the first set of clutch gear teeth  760  of the second output gear  738 , the biasing member is compressed while the selection clutch  722  engages the first set of clutch gear teeth  754  of the transfer shaft  736  and before the selection clutch  722  engages the first set of clutch gear teeth  760  of the second output gear  738 . 
     The first output gear  740  is a gear concentrically disposed within the second end portion of the input shaft  732 . The first output gear  740  is a substantially cup shaped body having an inner surface having gear teeth  772  formed on. As is known in the art, the first output gear  740  is known as a ring gear. The gear teeth  772  are engaged with the gear teeth formed on the outer surface of each of the driving pinions  734 . The first output gear  740  includes an output shaft  774  and first axle drive pinion  776  drivingly coupled thereto. Alternately, the first output gear  740  may be integrally formed with the output shaft  774 . The output shaft  774  is collinear with the input shaft  732 . Bearings disposed between the output shaft  774  and the housing support the output shaft  774  and permit the output shaft  774  to rotate about an axis of the output shaft  774 . The first axle drive pinion  776  is a spiral bevel gear the facilitates driving engagement between the axle output shaft  774  and the first axle drive assembly  718 ; however, it is understood that other type of gears may be used. 
     The first axle drive assembly  718  includes a first differential assembly  778  and a first drive axle  780 . The first differential assembly  778  and the first drive axle  780  are at least partially disposed in a first axle housing (not shown). The first differential assembly  778  is a conventional differential assembly comprising a ring gear, differential housing, drive pinions, and side gears as known in the art. The side gears of the first differential assembly  778  are respectively drivingly engaged with a first axle output shaft and the second axle output shaft of the first drive axle  780 . The ring gear of the first differential assembly  778  is drivingly engaged with the first axle drive pinion  776  to facilitate driving engagement between the first output gear  740  and the differential assembly. 
     The second axle drive assembly  720  includes an inter-axle assembly  782 , a second differential assembly  784 , a second drive axle  786 , and the axle disconnect clutch  724 . The second differential assembly  784 , the second drive axle  786 , and the axle disconnect clutch  724  are at least partially disposed in a second axle housing (not shown). The inter-axle assembly  782  comprises a geared shaft  788  in driving engagement with the second output gear  738 , a Cardan shaft  790  in driving engagement with the geared shaft  788 , and a second axle drive pinion  792  in driving engagement with the Cardan shaft  790 . The second differential assembly  784  is a conventional differential assembly comprising a ring gear, differential housing, drive pinions, and side gears as known in the art. The side gears of the second differential assembly  784  are respectively drivingly engaged with a first axle output shaft and the second axle output shaft of the second drive axle  786 . The ring gear of the second differential assembly  784  is drivingly engaged with the inter-axle assembly  782  to facilitate driving engagement between the second output gear  738  and the second differential assembly  784 . The second drive axle  786  comprises the first axle output shaft and the second axle output shaft. One of the first axle output shaft and the second axle output shaft may be divided into two portions by disengaging the axle disconnect clutch  724 . By disengaging the axle disconnect clutch  724 , the inter-axle assembly  782  and the second differential assembly  784  are prevented from being back-driven when the hybrid tandem axle drive unit  706  is placed in a single axle mode of operation. 
     In use, through control of the primary clutch  710 , the selection clutch  722 , and the axle disconnect clutch  724 , driving and charging can occur with and without engagement with the rest of the hybrid drivetrain  700 . The hybrid drivetrain  700  is a parallel post transmission hybrid drivetrain that allows the tandem axle drive unit  706  to be operated in a plurality of modes, as described hereinbelow. The motor generator  714  is placed inline in the hybrid driveline, and can be used to power or supplement the power source  702  for boosting or to recuperate the braking energy via the hybrid driveline  700  by applying torque to the planetary drive unit  716  or receiving torque from the drive axles  180 ,  786  via the planetary drive unit  716 . The motor generator  714  provides the following benefits: engine downsizing, efficiency improvement by operating the power source  702  within a narrower band (allowing the motor generator  714  to provide acceleration flexibility), reduced gearing in the transmission  704 , increased retrofitability, and increased functionality of a two speed electrified axle that increases performance of the hybrid driveline  700  having the motor generator  714  located in front of the planetary drive unit  716 . Further, it is understood that through the addition of the motor generator  714 , the controller  726 , and the battery  728 , a conventional driveline may be retrofitted to form the hybrid drivetrain  700 . It is also understood that the hybrid drivetrain  700  may be configured to implement techniques that improve an efficiency of the hybrid drivetrain  700 , such as, but not limited to, on-demand cylinder deactivation of a portion of the power source  702  via fuel shut off. 
       FIG.  8    is a schematic style view of a hybrid drivetrain  800  according to another embodiment of the application. The hybrid drivetrain  800  includes a power source  802 , a transmission  804 , and a hybrid tandem axle drive unit  894 , the hybrid tandem axle drive unit  894  including a first axle drive assembly  818  and a second axle drive assembly  820 . The power source  802  is drivingly engaged with an input of the transmission  804 . The hybrid tandem axle drive unit  894  is drivingly engaged with an output of the transmission  804  through a Cardan shaft  808 , for example. The hybrid drivetrain  800  is similar to the hybrid drivetrain  700  shown in  FIG.  7   , with the exception that the hybrid drivetrain  800  shown in  FIG.  8    includes a variation of the hybrid tandem axle drive unit  706 . In one embodiment of the hybrid drivetrain  800  includes a motor-generator  814  located after a planetary drive unit  816  and provides for operation at only a single operation speed of the hybrid drivetrain  800 . The variation of the application shown in  FIG.  8    includes similar components to the hybrid drivetrain  700  illustrated in  FIG.  7   . Similar features of the variation shown in  FIG.  8    are numbered similarly in series. Different and additional features of the variation shown in  FIG.  8    can be appreciated by one skilled in the art in view of  FIG.  8    and the hybrid drivetrain  700  illustrated in  FIG.  7   . 
     The hybrid tandem axle drive unit  894  is drivingly engaged with the transmission  804  through the Cardan shaft  808 . The hybrid tandem axle drive unit  894  comprises the planetary drive unit  816 , the motor-generator  814 , the first axle drive assembly  818 , and the second axle drive assembly  820 . The hybrid tandem axle drive unit  894  is configured to be placed in at least two modes of operation, depending on a position of a selection clutch  822  of the planetary drive unit  816 . In a first mode of operation, the hybrid tandem axle drive unit  894  operates in a high torque, dual axle mode operation. In a second mode of operation, the hybrid tandem axle drive unit  894  operates in a low torque, single axle mode operation. As shown in  FIG.  8   , the hybrid driveline  800  includes as optional an axle disconnect clutch  824  forming a portion of the second axle drive assembly  820 . 
     The motor-generator  814  is in driving engagement with the output shaft  874  of the first output gear  840  of the planetary drive unit  816 , The motor-generator  814  is in electrical communication with a controller  826  and a battery  828 . It is understood that the motor-generator  814 , or any of the other motor generators described herein, may be incorporated into a gearbox, transmission, or other driveline component of the hybrid drivetrain  800 . Depending on an electrical control of the motor-generator  814  using the controller  826 , the motor-generator  814  may apply force to or retard the output shaft  874  with which it is drivingly engaged with. 
       FIG.  9    is a schematic style view of a hybrid drivetrain  900  according to another embodiment of the application. The hybrid drivetrain  900  includes a power source  902 , a transmission  904 , and a hybrid tandem axle drive unit  996 , the hybrid tandem axle drive unit  996  including a first axle drive assembly  918  and a second axle drive unit assembly  920 . The power source  902  is drivingly engaged with an input of the transmission  904 . The hybrid tandem axle drive unit  996  is drivingly engaged with an output of the transmission  904  through a Cardan shaft  908 , for example. The hybrid drivetrain  900  is similar to the hybrid drivetrain  700  shown in  FIG.  7   , with the exception that the hybrid drivetrain  900  shown in  FIG.  9    includes a variation of the hybrid tandem axle drive unit  706 . The variation of the application shown in  FIG.  9    includes similar components to the hybrid drivetrain  700  illustrated in  FIG.  7   . Similar features of the variation shown in  FIG.  9    are numbered similarly in series. Different and additional features of the variation shown in  FIG.  9    can be appreciated by one skilled in the art in view of  FIG.  9    and the hybrid drivetrain  700  illustrated in  FIG.  7   . 
     The hybrid tandem axle drive unit  996  is drivingly engaged with the transmission  904  through the Cardan shaft  908 . The hybrid tandem axle drive unit  996  comprises a planetary drive unit  916 , the first axle drive assembly  918 , a motor-generator  914 , and the second axle drive assembly  920 . The hybrid tandem axle drive unit  996  is configured to be placed in at least two modes of operation, depending on a position of a selection clutch  922  of the planetary drive unit  916 . In a first mode of operation, the hybrid tandem axle drive unit  996  operates in a high torque, dual axle mode operation. In a second mode of operation, the hybrid tandem axle drive unit  996  operates in a low torque, single axle mode operation. As shown in  FIG.  9   , the hybrid driveline  900  includes as optional an axle disconnect clutch  924  forming a portion of the second axle drive assembly  920 . 
     The motor-generator  914  is in driving engagement with a geared shaft  988  of an inter-axle assembly  982  of the second axle drive assembly  920 . The motor-generator  914  is in electrical communication with a controller  926  and a battery  928 . It is understood that the motor-generator  914 , or any of the other motor generators described herein, may be incorporated into a gearbox, transmission, or other driveline component of the hybrid drivetrain  900 . 
     Depending on an electrical control of the motor-generator  914  using the controller  926 , the motor-generator  914  may apply force to or retard the geared shaft  988  with which it is drivingly engaged with. 
       FIG.  10    is a schematic style view of a hybrid drivetrain  1000  according to another embodiment of the application. The hybrid drivetrain  1000  includes a power source  1002 , a transmission  1004 , and a hybrid tandem axle drive unit  1098 , the hybrid tandem axle drive unit  1098  including a first axle drive assembly  1018  and a second axle drive assembly  1020 . The power source  1002  is drivingly engaged with an input of the transmission  1004 . The hybrid tandem axle drive unit  1098  is drivingly engaged with an output of the transmission  1004  through a Cardan shaft  1008 , for example. The hybrid drivetrain  1000  is similar to the hybrid drivetrain  700  shown in  FIG.  7   , with the exception that the hybrid drivetrain  1000  shown in  FIG.  10    includes a variation of the hybrid tandem axle drive unit  706 . The variation of the application shown in  FIG.  10    includes similar components to the hybrid drivetrain  700  illustrated in  FIG.  7   . Similar features of the variation shown in  FIG.  10    are numbered similarly in series. Different and additional features of the variation shown in  FIG.  10    can be appreciated by one skilled in the art in view of  FIG.  10    and the hybrid drivetrain  700  illustrated in  FIG.  7   . The hybrid tandem axle drive unit  1098  is drivingly engaged with the transmission  1004  through the Cardan shaft  1008 . The hybrid tandem axle drive unit  1098  comprises a planetary drive unit  1016 , the first axle drive assembly  018 , a motor-generator  1014 , and the second axle drive assembly  1020 . The hybrid tandem axle drive unit  1098  is configured to be placed in at least two modes of operation, depending on a position of a selection clutch  1022  of the planetary drive unit  1016 . In a first mode of operation, the hybrid tandem axle drive unit  1098  operates in a high torque, dual axle mode operation. In a second mode of operation, the hybrid tandem axle drive unit  1098  operates in a low torque, single axle mode operation. As shown in  FIG.  10   , the hybrid driveline  1000  includes as optional an axle disconnect clutch  1024  forming a portion of the second axle drive assembly  1020 . 
     The motor-generator  1014  is in driving engagement with a second axle drive pinion  1092  of an inter-axle assembly  1082  of the second axle drive assembly  1020 . The motor-generator  1014  is in electrical communication with a controller  1026  and a battery  1028 . It is understood that the motor-generator  1014 , or any of the other motor generators described herein, may be incorporated into a gearbox, transmission, or other driveline component of the hybrid drivetrain  1000 . Depending on an electrical control of the motor-generator  1014  using the controller  1026 , the motor-generator  1014  may apply force to or retard the second axle drive pinion  1092  with which it is drivingly engaged with. 
     In use, the hybrid drivetrain  700 ,  800 ,  900 ,  1000  may be operated in a plurality of operating modes. The hybrid drivetrain  700 ,  800 ,  900 ,  1000  may be operated in an all-electric mode, a hybrid mode, a regeneration/braking mode, a charging mode, and a direct drive mode. Further, it is understood that the operating modes described hereinbelow with respect to the hybrid drivetrain  700 ,  800 ,  900 ,  1000  may be adapted where necessary to utilize the architecture of each to operate in the all-electric mode (where applicable), the hybrid mode, the regeneration/braking mode, the charging mode, and the direct drive mode. 
     In embodiments of the all-electric mode, the primary clutch  710 ,  810 ,  910 ,  1010  is placed in a disengaged position, and the battery  728 ,  828 ,  928 ,  1028  serves as the only power source for the hybrid drivetrain  700 ,  800 ,  900 ,  1000  for the vehicle. In the all-electric mode, the hybrid tandem axle drive unit  706 ,  894 ,  996 ,  1098 , the motor-generator  714 ,  814 ,  914 ,  1014 , applies force to the hybrid drivetrain hybrid drivetrain  700 ,  800 ,  900 ,  1000 , causing rotation of at least one of the drive axles  780 ,  786 ,  880 ,  886 ,  980 ,  986 ,  1080 ,  1086 , depending on a position of the selection clutch  722 ,  822 ,  922 ,  1022  and a location of the motor-generator  714 ,  814 ,  914 ,  1014 , propelling the vehicle. In response to communication from the controller  726 ,  826 ,  926 ,  1026 , the primary clutch  710 ,  810 ,  910 ,  1010  is disengaged and the position of the selection clutch  722 ,  822 ,  922 ,  1022  is determined to operate the hybrid drivetrain  700 ,  800 ,  900 ,  1000  in the all-electric mode. 
     In the hybrid mode, the primary clutch  710 ,  810 ,  910 ,  1010  is placed in an engaged position, and the battery  728 ,  828 ,  928 ,  1028  and the power source  702 ,  802 ,  902 ,  1002  serve as a combined power source for the hybrid drivetrain  700 ,  800 ,  900 ,  1000 : In the hybrid mode, the motor-generator  714 ,  814 ,  914 ,  1014 , in addition to the power source  702 ,  802 ,  902 ,  1002 , may apply force to the hybrid drivetrain  700 ,  800 ,  900 ,  1000  to propel the vehicle. When the motor-generator  714 ,  814 ,  914 ,  1014  and the power source  702 ,  802 ,  902 ,  1002  are used in the hybrid mode, the primary clutch  710 ,  810 ,  910 ,  1010  is placed in an engaged position, and the motor-generator  714 ,  814 ,  914 ,  1014  and the power source  702 ,  802 ,  902 ,  1002 , in response to communication with the controller  726 ,  826 ,  926 ,  1026 , apply force to the hybrid drivetrain  700 ,  800 ,  900 ,  1000 , causing rotation of at least one of the drive axles  780 ,  786 ,  880 ,  886 ,  980 ,  986 ,  1080 ,  1086 , depending on a position of the selection clutch  722 ,  822 ,  922 ,  1022  and a location of the motor-generator  714 ,  814 ,  914 ,  1014 . 
     In the regeneration/braking mode, the motor-generator  714 ,  814 ,  914 ,  1014  is used to retard the hybrid drivetrain  700 ,  800 ,  900 ,  1000  for the vehicle to facilitate capturing kinetic energy of the vehicle as electrical power to be stored in the battery  728 ,  828 ,  928 ,  1028 . The regeneration/braking mode may be used to assist a conventional braking system or may be used to regulate a speed of the vehicle when descending an incline. When the motor-generator  714 ,  814 ,  914 ,  1014  is used in the regeneration/braking mode, the selection clutch  722 ,  822 ,  922 ,  1022  is placed in a position to facilitate driving engagement between at least one of the drive axles  780 ,  786 ,  880 ,  886 ,  980 ,  986 ,  1080 ,  1086  and the motor-generator  714 ,  814 ,  914 ,  1014  and the primary clutch  710 ,  810 ,  910 ,  1010  may be placed in a disengaged condition (it is understood that engine braking using the power source  702 ,  802 ,  902 ,  1002  may or may not be used in addition to the regeneration/braking mode), and the motor-generator  714 ,  814 ,  914 ,  1014  retards the hybrid drivetrain  700 ,  800 ,  900 ,  1000  to capture kinetic energy as electrical power. 
     In embodiments of the charging mode, the power source  702 ,  802 ,  902 ,  1002  and the first motor-generator  714 ,  814 ,  914 ,  1014  are used to charge the battery  728 ,  828 ,  928 ,  1028 . It is understood that the charging mode may be utilized when the vehicle is stationary (only applicable to the embodiment of the application shown in  FIG.  7   ) or when the power source  702 ,  802 ,  902 ,  1002  is propelling the vehicle through the hybrid drivetrain  700 ,  800 ,  900 ,  1000 . In the charging mode, the selection clutch  722 ,  822 ,  922 ,  022  is placed in a position to facilitate driving engagement between at least one of the drive axles  780 ,  786 ,  880 ,  886 ,  980 ,  986 ,  1080 ,  1086  and the motor-generator  714 ,  814 ,  914 ,  1014  and the primary clutch  710 ,  810 ,  910 ,  1010  is placed in an engaged condition, allowing the power source  702 ,  802 ,  902 ,  1002  and the motor-generator  714 ,  814 ,  914 ,  1014  to charge the battery  728 ,  828 ,  928 ,  1028 . 
     In the direct drive mode, the motor-generator  714 ,  814 ,  914 ,  1014  is not used to propel the vehicle. It is understood that the direct drive mode may be utilized when a charge level of the battery  728 ,  828 ,  928 ,  1028  does not permit operation in the all-electric or hybrid modes. In the direct drive mode, the primary clutch  710 ,  810 ,  910 ,  1010  is placed in an engaged position and the selection clutch  722 ,  822 ,  922 ,  1022  is placed in a position to facilitate driving engagement between at least one of the drive axles  780 ,  786 ,  880 ,  886 ,  980 ,  986 ,  1080 ,  1086  and the transmission  704 ,  804 ,  904 ,  1004 , and the power source  702 ,  802 ,  902 ,  1002  in response to communication with the controller  726 ,  826 ,  926 ,  1026 , applies force (motor-generator  714 ,  814 ,  914 ,  1014 , depending on the embodiment) to the hybrid drivetrain  700 ,  800 ,  900 ,  1000  to propel the vehicle. In accordance with the provisions of the patent statutes, the present application has been described in several embodiments, however, it should be noted that the application can be practiced otherwise than as specifically illustrated and described without departing from its scope or spirit. 
     It will be appreciated that the configurations and routines disclosed herein are exemplary in nature, and that these specific embodiments are not to be considered in a limiting sense, because numerous variations are possible. Moreover, unless explicitly stated to the contrary, the terms “first,” “second,” “third,” and the like are not intended to denote any order, position, quantity, or importance, but rather are used merely as labels to distinguish one element from another. The subject matter of the present disclosure includes all novel and non-obvious combinations and sub-combinations of the various systems and configurations, and other features, functions, and/or properties disclosed herein. 
     As used herein, the term “approximately” is construed to mean plus or minus five percent of the range unless otherwise specified. 
     The following claims particularly point out certain combinations and sub-combinations regarded as novel and non-obvious. These claims may refer to “an” element or “a first” element or the equivalent thereof. Such claims should be understood to include incorporation of one or more such elements, neither requiring nor excluding two or more such elements. Other combinations and sub-combinations of the disclosed features, functions, elements, and/or properties may be claimed through amendment of the present claims or through presentation of new claims in this or a related application. Such claims, whether broader, narrower, equal, or different in scope to the original claims, also are regarded as included within the subject matter of the present disclosure.