Abstract:
An electric vehicle powertrain according to an exemplary aspect of the present disclosure includes, among other things, a thermal barrier secured relative to an engine, a transaxle, or both to retain thermal energy generated during operation of an electric vehicle.

Description:
BACKGROUND 
       [0001]    This disclosure relates generally to an electric vehicle and, more particularly, to a thermal barrier to retain thermal energy within portions of an electric vehicle powertrain 
         [0002]    Generally, electric vehicles differ from conventional motor vehicles because electric vehicles are selectively driven using one or more battery-powered electric machines. Conventional motor vehicles, by contrast, rely exclusively on an internal combustion engine to drive the vehicle. Electric vehicles may use electric machines instead of, or in addition to, the internal combustion engine. 
         [0003]    Example electric vehicles include hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs), and battery electric vehicles (BEVs). Electric vehicles are typically equipped with a battery pack containing multiple battery cells that store electrical power for powering the electric machine. The battery cells may be charged prior to use, and recharged during a drive by a regenerative braking system or engine. 
         [0004]    When the electric vehicle is not operating, thermal energy from a powertrain of the electric vehicle moves to the surrounding environment. This movement of thermal energy lowers the temperature of the powertrain. Key mechanical elements of the powertrain operate more efficiently when their components are relatively hot. Operating the electric vehicle generates thermal energy, which can raise and maintain the temperature of the powertrain to temperatures corresponding to efficient operation. Efficiency improvements come primarily from two sources. 
         [0005]    The first source is the reduction of friction related losses in the engine and transaxle lubricating fluids. These fluids need less energy to airflow at higher temperatures due to reduced viscosity. 
         [0006]    The second source, often more important, is that a hybrid electric powertrain can only operate in fully electric mode (engine off) when the powertrain temperature reaches a certain threshold value. When the powertrain is below this critical temperature, the internal combustion engine stays on regardless of the power demand. Hence, the possibility to reduce fuel consumption by operating the vehicle in electric mode is compromised. 
         [0007]    Reaching the temperatures corresponding to efficient operation takes longer in relatively colder environments because the starting temperature of the components is lower. Further, after starting the electric vehicle in colder environments, some thermal energy is typically redirected to the cabin to comfort the driver. 
       SUMMARY 
       [0008]    An electric vehicle powertrain according to an exemplary aspect of the present disclosure includes, among other things, a thermal barrier secured relative to an engine, a transaxle, or both to retain thermal energy generated during operation of an electric vehicle. 
         [0009]    In a further, non-limiting embodiment of the foregoing electric vehicle powertrain, the thermal barrier is secured to an exterior surface. 
         [0010]    In a further, non-limiting embodiment of any of the foregoing electric vehicle powertrains, the thermal barrier is secured to an interior surface. 
         [0011]    In a further, non-limiting embodiment of any of the foregoing electric vehicle powertrains, the thermal barrier comprises an insulative panel. 
         [0012]    In a further, non-limiting embodiment of any of the foregoing electric vehicle powertrains, the thermal barrier comprises an integral portion of the engine or the transaxle. 
         [0013]    In a further, non-limiting embodiment of any of the foregoing electric vehicle powertrains, the thermal barrier is secured directly to an engine block of the engine. 
         [0014]    In a further, non-limiting embodiment of any of the foregoing electric vehicle powertrains, the thermal barrier is secured directly to a transaxle case of the transaxle. 
         [0015]    In a further, non-limiting embodiment of any of the foregoing electric vehicle powertrains, the thermal barrier is separate and distinct from the engine and the transaxle. 
         [0016]    In a further, non-limiting embodiment of any of the foregoing electric vehicle powertrains, at least one thermal barrier is secured to both the engine and the transaxle. 
         [0017]    In a further, non-limiting embodiment of any of the foregoing electric vehicle powertrains, the thermal barrier is an expandable insulation. 
         [0018]    In a further, non-limiting embodiment of any of the foregoing electric vehicle powertrains, the thermal barrier is a spray on insulation. 
         [0019]    In a further, non-limiting embodiment of any of the foregoing electric vehicle powertrains, the electric vehicle is a hybrid electric vehicle. 
         [0020]    In a further, non-limiting embodiment of any of the foregoing electric vehicle powertrains, a vehicle includes the electric vehicle powertrain, the vehicle includes a panel that is moveable between a retracted position that permits a first amount of airflow to the electric vehicle powertrain when the vehicle is operating, and an extended position that permits a second amount of airflow to the electric vehicle powertrain when the vehicle is not operating, the first amount of airflow greater than the second amount of airflow. 
         [0021]    In a further, non-limiting embodiment of any of the foregoing electric vehicle powertrains, a vehicle includes the electric vehicle powertrain, the vehicle includes at least one grille shutter that is moveable between a first position that permits a first amount of airflow to the electric vehicle powertrain when the vehicle is operating, and an second position that permits a second amount of airflow to the electric vehicle powertrain when the vehicle is not operating, the first amount of airflow greater than the second amount of airflow. 
         [0022]    A method of retaining thermal energy within an electric vehicle powertrain according to an exemplary aspect of the present disclosure includes, among other things, securing a thermal barrier to an engine, a transaxle, or both to retain thermal energy generated during operation of an electric vehicle. 
         [0023]    In a further-non-limiting embodiment of the foregoing method, the method includes securing the thermal barrier directly to an engine block of the engine, the thermal barrier separate and distinct from the engine block. 
         [0024]    In a further-non-limiting embodiment of any of the foregoing methods, the method includes securing the thermal barrier directly to transaxle case, the thermal barrier separate and distinct from the transaxle case. 
         [0025]    In a further-non-limiting embodiment of any of the foregoing methods, the method includes operating a vehicle that is propelled using the electric vehicle powertrain, and actuating at least one grille shutter between a first position that permits a first amount of airflow to the electric vehicle powertrain when the vehicle is operating, and a second position that permits a second amount of airflow to the electric vehicle powertrain when the vehicle is not operating, the first amount of airflow greater than the second amount of airflow. 
         [0026]    In a further-non-limiting embodiment of any of the foregoing methods, the method includes operating a vehicle that is propelled using the electric vehicle powertrain, and moving a panel between a retracted position that permits a first amount of airflow to the electric vehicle powertrain when the vehicle is operating, and an extended position that permits a second amount of airflow to the electric vehicle powertrain when the vehicle is not operating, the first amount of airflow greater than the second amount of airflow. 
     
    
     
       DESCRIPTION OF THE FIGURES 
         [0027]    The various features and advantages of the disclosed examples will become apparent to those skilled in the art from the detailed description. The figures that accompany the detailed description can be briefly described as follows: 
           [0028]      FIG. 1  illustrates a schematic view of an example powertrain architecture for an electric vehicle. 
           [0029]      FIG. 2  illustrates a highly schematic view of an engine of the powertrain of  FIG. 1 . 
           [0030]      FIG. 3  illustrates a perspective view of a transaxle assembly of the powertrain of  FIG. 1 . 
           [0031]      FIG. 4  illustrates a section view at line  4 - 4  in  FIG. 3 . 
           [0032]      FIG. 5  shows a highly schematic view of the engine of  FIG. 2  within an engine compartment. 
           [0033]      FIG. 6  shows a highly schematic view of the engine of  FIG. 2  within the engine compartment. 
       
    
    
     DETAILED DESCRIPTION 
       [0034]      FIG. 1  schematically illustrates a powertrain  10  for an electric vehicle. Although depicted as a hybrid electric vehicle (HEV), it should be understood that the concepts described herein are not limited to HEVs and could extend to other electrified vehicles, including, but not limited to, plug-in hybrid electric vehicles (PHEVs) and battery electric vehicles (BEVs). 
         [0035]    In one embodiment, the powertrain  10  is a powersplit hybrid electric propulsion system that employs a first drive system and a second drive system. The first drive system includes a combination of an engine  14  and a generator  18  (i.e., a first electric machine). The second drive system includes at least a motor  22  (i.e., a second electric machine), the generator  18 , and a battery pack  24 . In this example, the second drive system is considered an electric drive system of the powertrain  10 . The first and second drive systems generate torque to drive one or more sets of vehicle drive wheels  28  of the electric vehicle. 
         [0036]    The engine  14 , which is an internal combustion engine in this example, and the generator  18  may be connected through a power transfer unit  30 , such as a planetary gear set. Of course, other types of power transfer units, including other gear sets and transmissions, may be used to connect the engine  14  to the generator  18 . In one non-limiting embodiment, the power transfer unit  30  is a planetary gear set that includes a ring gear  32 , a sun gear  34 , and a carrier assembly  36 . 
         [0037]    The generator  18  may be driven by engine  14  through the power transfer unit  30  to convert mechanical energy to electrical energy. The generator  18  can alternatively function as a motor to convert electrical energy into mechanical energy, thereby outputting torque to a shaft  38  connected to the power transfer unit  30 . Because the generator  18  is operatively connected to the engine  14 , the speed of the engine  14  can be controlled by the generator  18 . 
         [0038]    The ring gear  32  of the power transfer unit  30  may be connected to a shaft  40 , which is connected to vehicle drive wheels  28  through a second power transfer unit  44 . The second power transfer unit  44  may include a gear set having a plurality of gears  46 . Other power transfer units may also be suitable. The gears  46  transfer torque from the engine  14  to a differential  48  to ultimately provide traction to the vehicle drive wheels  28 . The differential  48  may include a plurality of gears that enable the transfer of torque to the vehicle drive wheels  28 . In this example, the second power transfer unit  44  is mechanically coupled to an axle  50  through the differential  48  to distribute torque to the vehicle drive wheels  28 . 
         [0039]    The motor  22  (i.e., the second electric machine) can also be employed to drive the vehicle drive wheels  28  by outputting torque to a shaft  52  that is also connected to the second power transfer unit  44 . In one embodiment, the motor  22  can be used for regenerative braking in which the motor  22  absorbs torque from the wheels  28  through gears  48  and  42  and shaft  52  and outputs electrical power to the battery pack  24 . 
         [0040]    The battery pack  24  is an example type of electric vehicle battery assembly. The battery pack  24  may be a high voltage battery that is capable of outputting electrical power to operate the motor  22  and the generator  18 . Other types of energy storage devices and/or output devices can also be used with the electric vehicle. 
         [0041]    A transaxle assembly  56  includes, in this example, at least the motor  22  and the generator  18 . The power transfer unit  30  is also housed within the transaxle assembly  56 . 
         [0042]    Referring now to  FIG. 2  with continuing reference to  FIG. 1 , one or more thermal barriers  60  are secured to external surfaces  64  of the engine  14  to retain thermal energy within the engine  14 . The thermal energy may be generated by the engine  14  during operation. The thermal barrier  60  slows movement of thermal energy from the engine  14 . The engine  14  thus retains thermal energy longer than another engine that does not include thermal barriers  60 . 
         [0043]    In place of, or in addition to, the thermal barriers  60 , at least one internal thermal barrier  60   a  may be secured against an internal surface  68  of the engine  14 . The internal thermal barrier  60   a  slows movement of thermal energy from the engine  14 . The engine  14  thus retains thermal energy for a longer period than if the engine  14  lacked the internal thermal barrier  60   a.    
         [0044]    The external surfaces  64  of the engine  14  correspond generally to the outermost surfaces of the engine  14 , such as the outermost surfaces of an engine block. The external surfaces  64  face outwardly away from other portions of the engine  14 . The internal surfaces  68  correspond to other surfaces of the engine  14 , such as the surfaces establishing cylinders or other cavities within the engine  14 . 
         [0045]    In some examples, the thermal barrier  60   a  is an expandable insulation blown through portions of the engine  14 . During installation, the insulation expands against the internal surfaces  68  to hold the position of the insulation and provide the thermal barrier  60   a.    
         [0046]    Notably, the internal thermal barrier  60   a  may experience a longer life when compared to the thermal barrier  60 . The longer life is due to lessened durability concerns because of its location internal to the engine  14 . The internal thermal barrier  60   a  is internal to the engine  14  and less exposed to natural elements than the thermal barrier  60  secured to the external surfaces  64  of the engine  14 . 
         [0047]    In some examples, the engine  14  is designed to include one or more cavities or channels  76 . A thermal barrier  60 ′ is sized to be received within the channel  76 . The thermal barrier  60 ′ may be an expandable insulation blown into the channel  76  and expands against the walls of the channels  76  to hold the expandable insulation and provide the thermal barrier. 
         [0048]    The thermal barriers  60 ,  60 ′ and  60   a  could also comprise spray on insulation in some examples. 
         [0049]    The thermal barriers  60 ,  60 ′ and  60   a  cause the engine  14  to retain heat more effectively than an engine lacking thermal barriers. The retained heat allows the engine  14  to start from a higher temperature relative to an engine lacking thermal barriers. Thermal energy convects away from the engine  14  more slowly than in another engine lacking the thermal barriers. 
         [0050]    In this example, the barriers  60 ,  60 ′, and  60   a  can be insulative panels that are directly secured to the engine  14 . The barriers  60 ,  60 ′ and  60   a  can also be separate and distinct from the engine  14 . The barriers  60 ,  60 ′ and  60   a  can be flame retardant, non-toxic, and relatively lightweight. 
         [0051]    The engine  14 , including the cylinder head, engine block, and the oil pan area, can have thermal barriers  60 ,  60 ′, and  60   a  to slow down the rate of heat loss. If the thermal barriers  60 ,  60 ′, and  60   a  are insulation panels, they can be secured by screws or other mechanical fastening devices to the external or internal surfaces of the engine  14 . Alternatively, the thermal barriers  60 ,  60 ′, and  60   a  can be secured in place by adhesives or deposited on the surface by some suitable industrial process. 
         [0052]    Referring now to  FIGS. 3 and 4 , the transaxle  56  may include thermal barriers  80  that are secured to exterior surfaces  84  of the transaxle  56 . Other thermal barriers (not shown) may be secured to internal surfaces of the transaxle  56  instead of, or in addition to, the thermal barrier  80  secured to the external surface  84 . 
         [0053]    The thermal barrier  80  can be secured to the external surface  84  with a screw  88 , or another type of mechanical fastener, adhesive, etc. In this example, the screws  88  are threaded into the transaxle  56 . 
         [0054]    One or more channels  92  or pockets can be provided in the transaxle  56  to receive a blown expandable insulation that provides another thermal barrier  80 ′. 
         [0055]    Referring now to  FIGS. 5 and 6 , a contributing factor to thermal energy moving from the engine  14  and the transaxle  56  (not shown) is a flow F of air, for example, around the engine  14  and the transaxle  56 , even when the vehicle associated with the engine  14  and the transaxle  56  is not running. The airflow F moves from the area surrounding an engine compartment  108  across the engine  14 . 
         [0056]    In this example, a movable device  100  is moved to a first position ( FIG. 5 ) to limit cold air from an exterior of the vehicle from entering an interior  104  of the engine compartment  108 . A controller C is configured to actuate the movable device  100  between the position shown in  FIG. 5  that prevents less airflow into the interior  104 , and the position shown in  FIG. 6  that permits more airflow into the interior  104 . The controller C may actuate the moveable device  100  in response to temperature. For example, the controller C may cause the moveable device  100  to move to the position of  FIG. 5  when an air temperature outside the interior  104  is less than the temperature inside  104  by a pre-determined amount, such as 10 degrees F., for example. 
         [0057]    Typically, the moveable device  100  is not utilized as described above if there is only a relatively small difference between the temperature of the interior  104  and the temperature outside the engine compartment  108 . Preventing a small amount of heat loss would not justify the energy, such as electricity, used to actuate the movable device  100 , for example. 
         [0058]    The position of the moveable device  100  shown in  FIG. 6  corresponds to the desired position for the moveable device  100  when the vehicle is operating and the engine  14  is generating thermal energy. The position of the moveable device  100  can be selectively varied to permit more or less airflow into the interior  104 . 
         [0059]    In this example, the movable device  100  is a panel that is selectively extended to block airflow into the interior  104  for when the vehicle is not operating, and retracted to permit airflow into the interior  104  when the vehicle is operating. 
         [0060]    In another example, the movable device  100  comprises one or more grille shutters that are actively moved and rotated by the controller  112  between positions that permit more airflow and positions that permit less airflow. 
         [0061]    Features of the disclosed examples include improved fuel economy gains due to thermal energy retained within an engine of an electric vehicle, a transaxle, or both. The thermal barriers facilitate starting the electric vehicle powertrain with components having a higher internal temperature than if components did not include thermal barriers. The thermal barriers cause the components to heat at a faster rate than if the components did not include thermal barriers. The thermal barriers also may reduce noise emission from the engine, the transaxle, and other areas of the electric vehicle powertrain. 
         [0062]    The preceding description is exemplary rather than limiting in nature. Variations and modifications to the disclosed examples may become apparent to those skilled in the art that do not necessarily depart from the essence of this disclosure. Thus, the scope of legal protection given to this disclosure can only be determined by studying the following claims.