Abstract:
An exemplary method includes circulating a fluid through a heat exchanger and a battery pack when the battery pack requires cooling, and circulating the fluid through an exhaust gas heat recovery device and the battery pack when the battery pack requires heating. An exemplary system includes a battery pack, a heat exchanger, an exhaust gas heat recovery device, and a fluid valve moveable to a cooling position that permits a fluid to circulate between the heat exchanger and the battery pack and a heating position that permits the fluid to circulate between the exhaust gas heat recovery device and the battery pack.

Description:
TECHNICAL FIELD 
       [0001]    This disclosure relates to managing thermal energy levels of a traction battery and, more particularly, to selective heating of the traction battery using an exhaust gas heat recovery device. 
       BACKGROUND 
       [0002]    Generally, electrified vehicles differ from conventional motor vehicles because electrified vehicles are selectively driven using one or more battery-powered electric machines. Conventional motor vehicles, in contrast to electrified vehicles, are driven exclusively using an internal combustion engine. The electric machines can drive the electrified vehicles instead of, or in addition to, an internal combustion engine. Example electrified vehicles include hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs), fuel cell vehicles (FCVs), and battery electric vehicles (BEVs). 
         [0003]    Traction batteries of electrified vehicles have an optimal operating temperature range. Operating the traction battery within the optimal operating temperature range can, among other things, improve the operational efficiency of the traction battery. Heating or cooling the traction battery can be required to bring the traction battery within the optimal operating temperature range. 
       SUMMARY 
       [0004]    A method according to an exemplary aspect of the present disclosure includes, among other things, circulating a fluid through a heat exchanger and a battery pack when the battery pack requires cooling, and circulating the fluid through an exhaust gas heat recovery device and the battery pack when the battery pack requires heating. 
         [0005]    In a further non-limiting embodiment of the foregoing method, the method includes directing an exhaust gas from the engine through the exhaust gas heat recovery device when the battery pack requires heating, and bypassing the exhaust gas from the engine around the exhaust gas heat recovery device when the battery pack requires cooling. 
         [0006]    In a further non-limiting embodiment of any of the foregoing methods, the method includes circulating the fluid through the exhaust gas heat recovery device when the battery pack requires cooling. 
         [0007]    In a further non-limiting embodiment of any of the foregoing methods, the method further includes bypassing the fluid around the heat exchanger when the battery pack requires heating. 
         [0008]    In a further non-limiting embodiment of any of the foregoing methods, the method includes powering a drive wheel of an electrified vehicle using power from the battery pack. 
         [0009]    In a further non-limiting embodiment of any of the foregoing methods, the method includes removing thermal energy from the fluid at the heat exchanger when the battery pack requires cooling. 
         [0010]    In a further non-limiting embodiment of any of the foregoing methods, the method includes adding thermal energy to the fluid at the exhaust gas heat recovery device when the battery pack requires heating. 
         [0011]    In a further non-limiting embodiment of any of the foregoing methods, the method includes heating the exhaust gas heat recovery device with an exhaust gas from an internal combustion engine. 
         [0012]    In a further non-limiting embodiment of any of the foregoing methods, the fluid is a liquid. 
         [0013]    In a further non-limiting embodiment of any of the foregoing methods, the heat exchanger is a radiator. 
         [0014]    A system according to an exemplary aspect of the present disclosure includes, among other things, a battery pack, a heat exchanger, an exhaust gas heat recovery device, and a fluid valve moveable to a cooling position that permits a fluid to circulate between the heat exchanger and the battery pack and a heating position that permits the fluid to circulate between the exhaust gas heat recovery device and the battery pack. 
         [0015]    In a further non-limiting embodiment of the foregoing system, the assembly includes a gas valve moveable to a recovery position that directs an exhaust gas to flow through the exhaust gas heat recovery device when the fluid valve is in the heating position and a bypass position that directs the exhaust gas to bypass around the exhaust gas heat recovery device when the fluid valve is in the cooling position. 
         [0016]    In a further non-limiting embodiment of any of the foregoing systems, the flow moves through the exhaust gas heat recovery device when the fluid valve is in the cooling position. 
         [0017]    In a further non-limiting embodiment of any of the foregoing systems, the flow bypasses around the heat exchanger when the fluid valve is in the heating position. 
         [0018]    In a further non-limiting embodiment of any of the foregoing systems, the battery pack is a traction battery pack that powers a drive wheel of an electrified vehicle. 
         [0019]    In a further non-limiting embodiment of any of the foregoing systems, the assembly includes an internal combustion engine that provide the exhaust gas. 
         [0020]    In a further non-limiting embodiment of any of the foregoing systems, the heat exchanger is configured to communicate thermal energy from the fluid when the fluid valve is in the cooling position. 
         [0021]    In a further non-limiting embodiment of any of the foregoing systems, the exhaust gas heat recovery device is configured to communicate thermal energy to the fluid when the fluid valve is in the heating position. 
         [0022]    In a further non-limiting embodiment of any of the foregoing systems, the heat exchanger is a radiator. 
     
    
     
       DESCRIPTION OF THE FIGURES 
         [0023]    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: 
           [0024]      FIG. 1  schematically illustrates an example powertrain of a hybrid electric vehicle. 
           [0025]      FIG. 2  schematically illustrates a thermal management system when heating a battery pack of the powertrain of  FIG. 1 . 
           [0026]      FIG. 3  schematically illustrates the thermal management system of  FIG. 2  when cooling the battery pack of the powertrain of  FIG. 1 . 
       
    
    
     DETAILED DESCRIPTION 
       [0027]    This disclosure relates generally to heating and cooling a battery pack of an electrified vehicle. During the heating, an exhaust gas heat recovery (“EGHR”) device heats a fluid. Heated fluid from the EGHR devices moves through the battery pack to heat the battery pack. During the cooling, the same fluid moves through the battery pack to cool the battery pack. 
         [0028]    Referring to  FIG. 1 , a powertrain  10  of a hybrid electric vehicle (HEV) includes a battery pack  14  having a plurality of arrays  18 , an internal combustion engine  20 , a motor  22 , and a generator  24 . The motor  22  and the generator  24  are types of electric machines. The motor  22  and generator  24  may be separate or have the form of a combined motor-generator. 
         [0029]    In this embodiment, the powertrain  10  is a power-split powertrain that employs a first drive system and a second drive system. The first and second drive systems generate torque to drive one or more sets of vehicle drive wheels  28 . The first drive system includes a combination of the engine  20  and the generator  24 . The second drive system includes at least the motor  22 , the generator  24 , and the battery pack  14 . The motor  22  and the generator  24  are portions of an electric drive system of the powertrain  10 . 
         [0030]    The engine  20  and the generator  24  can 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, can be used to connect the engine  20  to the generator  24 . 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 . 
         [0031]    The generator  24  can be driven by the engine  20  through the power transfer unit  30  to convert kinetic energy to electrical energy. The generator  24  can alternatively function as a motor to convert electrical energy into kinetic energy, thereby outputting torque to a shaft  38  connected to the power transfer unit  30 . 
         [0032]    The ring gear  32  of the power transfer unit  30  is connected to a shaft  40 , which is connected to the 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 could be used in other examples. 
         [0033]    The gears  46  transfer torque from the engine  20  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 . 
         [0034]    The motor  22  can be selectively employed to drive the vehicle drive wheels  28  by outputting torque to a shaft  54  that is also connected to the second power transfer unit  44 . In this embodiment, the motor  22  and the generator  24  cooperate as part of a regenerative braking system in which both the motor  22  and the generator  24  can be employed as motors to output torque. For example, the motor  22  and the generator  24  can each output electrical power to recharge cells of the battery pack  14 . 
         [0035]    The arrays  18  of the battery pack  14  include battery cells. Operating the battery cells and other portions of the battery pack  14  within an optimal temperature range can, among other things, facilitate efficient operation. The optimal temperature range for some types of battery packs  14  can be from 20 to 40 degrees Celsius, for example. 
         [0036]    Referring now to  FIGS. 2 and 3  with continuing reference to  FIG. 1 , an example thermal management system  60  selectively heats or cools the battery pack  14  to bring the battery pack  14  to be within, or closer to, the optimal temperature range. 
         [0037]    When the temperatures of the battery cells, or another portion of the battery pack  14 , are below an optimal temperature range, the system  60  can add thermal energy to the battery pack  14 . When the temperature of the battery cells within the battery pack  14  are above an optimal temperature range, the system  60  can remove thermal energy from the battery pack  14 . The system  60  thus selectively heats or cools the battery pack  14 . The system  60  can heat or cool portions of the battery pack  14 , such as battery cells of selected arrays  18 , rather than the entire battery pack  14 . 
         [0038]    In this example, the system  60  includes the battery pack  14 , an EGHR device  64 , a heat exchanger  68 , a fluid valve  72 , a gas valve  74 , an adjustable fluid path  76 , and an adjustable exhaust gas flow path  78 . A pump  80  can be used to move a fluid along the fluid path  76 . The fluid is a liquid coolant in this example. In another example, the fluid could be a gas, such as air. 
         [0039]    In this example, the fluid valve  72  can be actuated back and forth between a heating position and a cooling position. The fluid path  76  adjusts depending on the positioning of the fluid valve  72 .  FIG. 2  illustrates an example of the fluid path  76  when the fluid valve  72  is in the heating position.  FIG. 3  illustrates an example of the fluid path  76  when the fluid valve  72  is in the cooling position. 
         [0040]    When the fluid valve  72  is in the heating position, fluid moves along the fluid path  76  and carries thermal energy to the battery pack  14  to provide heating. When the fluid valve  72  is in the cooling position, fluid moves along the fluid path  76  and carries thermal energy from the battery pack  14  to provide cooling. 
         [0041]    When the fluid valve  72  is in the heating position, the fluid path  76  extends from the battery pack  14 , to the EGHR device  64 , to the fluid valve  72 , and then back to the battery pack  14 . The fluid path  76  thus bypasses around the heat exchanger  68  when the fluid valve  72  is in the heating position. 
         [0042]    The gas valve  74  is adjustable between a recovery position that directs exhaust gas to flow through the EGHR device  64  and a bypass position that directs the exhaust gas to bypass around the exhaust gas heat recovery device. 
         [0043]    When the fluid valve  72  is in the heating position, the gas valve  74  is adjusted to the recovery position to cause the exhaust gas flow path  78  to extend through the EGHR device  64 . Thus, when the fluid valve  72  is in the heating position, the EGHR device  64  receives a flow of exhaust gas from the engine  20 . When the exhaust gas is moving through the EGHR device  64 , the fluid moving along the fluid path  76  that is exiting the EGHR device  64  is heated relative to the fluid entering the EGHR device  64 . The exhaust gas heats the fluid within the EGHR device  64 . 
         [0044]    The EGHR device  64  is a type of heat exchanger that transfers thermal energy from the exhaust gas to the fluid within the fluid path  76 . The EGHR device  64  recovers waste heat as most of the thermal energy within the exhaust gas is expelled to ambient if not moved through the EGHR device  64 . 
         [0045]    Several types of heat transfer could be used by the EGHR device  64  to transfer heat to the fluid within the fluid path including, but not limited to, conduction, convection, advection, and radiation. 
         [0046]    The fluid within the fluid path  76  circulates between the battery pack  14  and the EGHR device such that the fluid carries thermal energy from the EGHR device  64  to the battery pack  14  when the fluid valve  72  is in the heating position. Because the fluid valve  72  in the heating position bypasses the fluid from the EGHR device  64  around the heat exchanger  68 , the fluid that has been heated within the EGHR device  64  will not cool due to communication through the heat exchanger  68 . 
         [0047]    When the fluid valve  72  is in the cooling position, the fluid path  76  extends from the battery pack  14 , to the EGHR device  64 , to the fluid valve  72 , to the heat exchanger  68 , and then back to the battery pack  14 . The fluid within the fluid path  76  circulates between the battery pack  14  and the heat exchanger  68  to carry thermal energy from the battery pack  14  to the heat exchanger  68  when the fluid valve  72  is in the cooling position. 
         [0048]    The heat exchanger  68  is a type of heat exchanger that removes thermal energy from fluid moving along the fluid path within the heat exchanger  68 . The heat exchanger  68  is a radiator in this example. Within the heat exchanger  68 , the fluid moving along the fluid path  76  can be cooled by surrounding air. Thermal energy from the fluid moves to ambient at  92 . The fluid moving along the fluid path  76  that is exiting the heat exchanger  68  is thus cooled relative to the fluid entering the heat exchanger  68 . 
         [0049]    Several types of heat transfer could be used by the heat exchanger  68  to transfer heat from the fluid within the fluid path including, but not limited to, conduction, convection, advection, and radiation. 
         [0050]    When the fluid valve  72  is in the cooling position, the gas valve  74  is adjusted to the bypass position to cause the exhaust gas to bypass around the EGHR device  64 . Bypassing the exhaust gas around the EGHR device  64  ensures that thermal energy is not added to the fluid within the fluid path  76  when cooling the battery pack  14  is desired. 
         [0051]    The gas valve  74  can adjust the exhaust gas flow path to direct the exhaust gas to the EGHR device  64 , to bypass the exhaust gas around the EGHR device  64 , or some combination of these. 
         [0052]    The system  60  can include a controller  94  that is operably coupled to one or more temperature sensors  96  within the battery pack  14 , the fluid valve  72 , and the gas valve  74 . The controller  94  can be further operably coupled to temperature sensors outside the battery pack  14 , such as temperature sensors  98  that monitor temperatures of the fluid moving along the fluid path  76 . 
         [0053]    The controller  94  is configured to move the fluid valve  72  between the heating and cooling positions. The controller  94  can move the fluid valve  72  in response to temperature measurements from the sensors  96 , the sensors  98 , or in response to some other input. 
         [0054]    In some examples, during startup in cold ambient conditions, the controller  94  moves the fluid valve  72  to the heating position and moves the gas valve  74  to a position that directs flow through the EGHR device  64 . This positioning of the fluid valve  72  and the gas valve  74  causes fluid in the fluid path  76  to heat areas of the battery pack  14 , which can raise or maintain temperatures of the battery pack  14  closer to the desired operating temperature range. 
         [0055]    After the temperatures of the battery pack  14  has increased, the controller  94  can then move the fluid valve  72  the cooling position and the gas valve  74  to a position that bypasses exhaust flow around the EGHR device  64 . This positioning of the fluid valve  72  and the gas valve  74  causes fluid in the fluid path  76  to cool areas of the battery pack  14 , which can reduce or maintain temperatures of the battery pack  14  closer to the desired operating temperature range. 
         [0056]    The controller  94  can be a portion of a battery electronic control module (BECM) containing circuitry utilized for retrieving data from the sensors  96 ,  98 , and for controlling the positioning of the fluid valve  72  and the gas valve  74 . The controller  94  could be outside the BECM in other examples. 
         [0057]    The fluid valve  72  is a valve that can be actuated to regulate the fluid within the fluid path  76 . The fluid valve  72  is responsive to signals from the controller  94 . In some examples, the controller  94  is eliminated and the fluid valve  72  is responsive instead to signals from the temperature sensors  96 ,  98 . The fluid valve  72  could be a ball valve, gate valve, butterfly valve, or some other type of valve suitable for regulating fluid flow. 
         [0058]    In some examples, the fluid valve  72  can be adjusted to heating positions or cooling positions where some fluid moving along the fluid path  76  bypasses the heat exchanger  68  and some fluid moving along the fluid path moves through the heat exchanger  68 . Such positions may be desired if less cooling or less heating is desired. 
         [0059]    The gas valve  74  is a valve that can be actuated to regulate the flow of exhaust gas from the engine  20 . The gas valve  74  is responsive to signals from the controller  94 . In some examples, the controller  94  is eliminated and the gas valve  74  is responsive instead to signals from the temperature sensors  96 ,  98 . The gas valve  74  could be a ball valve, gate valve, butterfly valve, or some other type of valve suitable for regulating fluid flow. 
         [0060]    In some examples, the gas valve  74  can be adjusted to positions where some flow is direct through the EGHR device  64  and some flow is bypassed around the EGHR device  64 . Such positions may be desired if reduced heating of fluid moving along the fluid path  76  within the EGHR device  64  is desired. 
         [0061]    Features of the disclosed examples include heating battery cells and other portions of a battery pack  14  using thermal energy from the exhaust gas and without requiring a separate heater. Additional heating elements could be added to the system  60  if further heating is desired. 
         [0062]    Another feature of the system  60  is improved fuel economy in cold ambient temperatures due to the battery cells of the battery pack  14  reaching an optimal temperature range more quickly due to thermal energy from the exhaust gas. 
         [0063]    The system  60  is particularly applicable to single motor battery limited modified hybrid transmission electrified vehicle architectures where full battery power discharge limits can be required for optimal start-stop operation and fuel efficiency. 
         [0064]    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.