Abstract:
A Lithium Ion battery cooling system for use in a hybrid vehicle comprises a plurality of self-contained liquid cooling modules, each cooling module including a closed and sealed container having an interior space. Each cooling module includes a battery assembly disposed within the interior space of the container and a plurality of battery cells having at least one fluid channel formed therebetween for receiving a fluid therein. A dielectric fluid is disposed within the at least one fluid channel. The dielectric fluid substantially immerses and is in contact with the battery assembly to heat and cool the battery assembly. A heating element is disposed within the interior space and heats the dielectric fluid. A cooling element is disposed within the interior space and cools the dielectric fluid.

Description:
FIELD OF THE INVENTION 
     The present disclosure relates to a vehicle battery pack with a self-contained liquid cooling system. 
     BACKGROUND OF THE DISCLOSURE 
     A battery cell has been proposed as a clean, efficient and environmentally responsible power source for electric vehicles and various other applications. One type of battery cell is known as the lithium-ion battery. The lithium-ion battery is rechargeable and can be formed into a wide variety of shapes and sizes so as to efficiently fill available space in electric vehicles. For example, the battery cell may be prismatic in shape to facilitate a stacking of the battery cells. A plurality of individual battery cells can be provided in a battery pack to provide an amount of power sufficient to operate electric vehicles. 
     Typical prismatic battery cells have a pair of plastic coated metal layers fused around a periphery of the battery cell in order to seal the battery cell components. The sealing of the battery cells generally begins with providing one of the plastic coated metal layers with a cavity, sometimes called a “butter dish” shape. The battery cell components are disposed inside the cavity of the plastic coated metal layer. The other of the plastic coated metal layers is then placed on top of the battery cell components and fused at the periphery to the one of the plastic coated metal layers with the cavity, for example, by heat sealing around the edges. The battery cell for incorporation in a battery pack assembly is thereby provided. 
     Battery cells such as lithium-ion battery cells are known to generate heat during operation and as a result of a charge cycle when recharging. When overheated or otherwise exposed to high-temperature environments, undesirable effects can impact the operation of lithium-ion batteries. Cooling systems are typically employed with lithium-ion battery packs to militate against the undesirable overheating conditions. The cooling systems may include cooling plates or fins sandwiched between individual battery cells within the battery pack. The cooling system may have channels through which a coolant flows in a heat transfer relationship with the battery cells. Nonlimiting examples of known cooling systems for battery cells are described in Assignee&#39;s co-pending U.S. patent application Ser. No. 12/713,729 to Essinger et al. and U.S. patent application Ser. No. 12/842,478 to Kumar et al., the entire disclosures of which are hereby incorporated herein by reference. 
     Conventional cooling systems have included air to air cooling, cooling plates or fins sandwiched between individual battery cells within the battery pack along with heat sinks in the same location. 
     There is a continuing need for a battery cooling system and a method for making the battery cooling system that maximizes efficient heating and cooling of the battery cells with minimum delta temperatures. Desirably, the battery cooling system and method maintains uniform surface temperatures over the battery cells and efficiently transfers heat away from the cells using open bath cooling in a hybrid vehicle. 
     SUMMARY OF THE INVENTION 
     In concordance with the instant disclosure, a battery cooling system and method of cooling a battery pack is surprisingly discovered. In a first embodiment, a vehicle battery pack with a self-contained liquid cooling system comprises a sealed container having an interior space; a battery assembly disposed within the interior space of the container, the battery assembly including a plurality of battery cells having at least one fluid channel formed therebetween; a dielectric fluid disposed within the at least one fluid channel in contact with the battery cells of the battery assembly and configured to heat and cool the battery assembly; a heating element disposed within the interior space configured to heat the dielectric fluid; and a cooling element disposed within the interior space configured to cool the dielectric fluid. 
     In another embodiment, a Lithium Ion battery cooling system for use in a hybrid vehicle comprises a plurality of self-contained liquid cooling modules, each of the cooling modules further comprises a sealed container having an interior space; a battery assembly disposed within the interior space of the container and including a plurality of battery cells having at least one fluid channel formed therebetween; a dielectric fluid disposed within the at least one fluid channel in contact with the battery cells of the battery assembly and configured to heat and cool the battery assembly; a heating element disposed within the interior space configured to heat the dielectric fluid; and a cooling element disposed within the interior space configured to cool the dielectric fluid. 
     In a further embodiment, a method of cooling a vehicle battery pack comprises the steps of: providing a sealed container having an interior space; providing a battery assembly within the interior space of the container and including a plurality of battery cells having at least one fluid channel formed therebetween; providing a dielectric fluid within the interior space; immersing at least a portion of the battery assembly with the dielectric fluid; causing the dielectric fluid to flow about the plurality of battery cells throughout the interior space of the container; and cooling the dielectric fluid during operation of the vehicle to maintain a substantially uniform surface temperature over each of the plurality battery cells. 
    
    
     
       DRAWINGS 
       The above, as well as other advantages of the present disclosure, will become readily apparent to those skilled in the art from the following detailed description, particularly when considered in the light of the drawings described herein. 
         FIG. 1  is a schematic view of the battery cooling system of the present disclosure; and 
         FIG. 2  is a plan view of multiple battery cooling systems of the present invention connected in series. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The following detailed description and appended drawing describes and illustrates an embodiment of the invention. The description and the drawing serve to enable one skilled in the art to make and use the invention, and are not intended to limit the scope of the invention in any manner. In respect of the methods disclosed, the steps presented are exemplary in nature, and thus, the order of the steps is not necessary or critical. 
     With reference to  FIG. 1 , a vehicle battery pack with a self-contained liquid cooling system  10  of the present disclosure is there shown. The system  10  is a module  12  formed of a container  14  with an interior space  16  for supporting a battery assembly  18 . The container  14  is a closed and sealed container  14  for forming a self-contained liquid cooling system  10 . In one embodiment, the battery assembly  18  includes a plurality of battery cells  20  such as a plurality of Lithium-ion (Li-ion) batteries for use in a hybrid vehicle. In another embodiment, the plurality of battery cells  20  is Li-ion batteries for use in a Battery Electric Vehicle (BEV). Additional batteries for use with other prime mover vehicles may be provided with the liquid cooling system  10  of the present invention, where each battery cell includes active material for generating power from an electrochemical reaction within the interior space  16  of the container  14 . The battery cells  20  are preferably stacked to form a battery cell stack  22 . In the embodiment shown, a gap  24  between each battery cell  20  is between 0.25-0.50 mm, forming a fluid channel  26  between each battery cell  20 . In another embodiment, the gap  24  may be less than 0.25 mm. It is understood that other gap sizes can be used as desired. 
     A dielectric coolant  28  is disposed within the interior space  16  of the container  14  and the fluid level shown is such that the battery assembly  18  is completely immersed within the dielectric coolant  28 . The dielectric coolant  28  is in contact with the battery cells  20  through the fluid channels  26  formed by gaps  24 . In one embodiment, the dielectric coolant  28  may be halogenated. In another embodiment, the dielectric coolant  28  may be conditioned to have a boiling point at or near a desired operating temperature of the battery cells  20 . 
     A heating element  34  is located at a base area  36  of the container  14 . The heating element  34  shown is an electronic heating element. It is understood that other heating element types may be used. The heating element  34  is shown as a single element; however, multiple heating elements  34  such as heating plates may be provided. 
     A cooling element  38  is located at an upper area  40  of the container  14 . The cooling element  38  may be a chilled water condenser having an inlet  42  and an outlet  44  extending beyond the walls of the sealed container  14  for importing and exporting water for the cooling element  38 . In another embodiment, the cooling element  38  may be a chilled water plate. In still another embodiment, the cooling element  38  may be a thin aluminum heat sink having external chilled water travelling through the cooling element  38 . The cooling element  38  may be a graphite foil impregnated with an electrically nonconductive polymer. The cooling element may also be formed from copper. 
     In the embodiment shown, arrows “A” and “B” indicate a flow of the dielectric coolant  28 . Upon heating of each battery cell  20  by the heating element  34 , the dielectric coolant  28  exposed to a front surface area  30  and a rear surface area  32  of the battery cells  20 , will boil. The heated dielectric coolant  28  will rise and flow to the top of the battery cell stack  22  to be cooled by the cooling element  38 . The cooled dielectric coolant  28  will return to the base area  36 , generally following either coolant paths “A” or “B.” Where the general location of the dielectric coolant  28  at the moment of boiling is located within the fluid channels  26  of the battery cells  20  in the center area and toward a side  50  of the container  14 , the dielectric coolant  28  will tend to follow flow path “A”. Similarly, if the general location of the dielectric coolant  28  at the moment of boiling is located within the fluid channels  26  of the battery cells  20  in the center area and toward an opposing side  52  of the container  14 , the dielectric coolant  28  will tend to follow flow path “B”. 
     A coolant temperature sensor  46  is located on or near the cooling element  38 . In the embodiment shown, the temperature sensor  46  is located within the area of the outlet  44  of the cooling element  38  and measures a temperature of the dielectric coolant  28  at a point of exposure to the cooling element. The temperature sensor  46  may be located anywhere within the battery cell stack  22  as desired. 
     A coolant level sensor  48  is also provided and is located near the upper area  40  of the container  14  to measure the fluid level of the dielectric coolant  28  within the container  14 , ensuring complete immersion of the battery assembly  18  within the dielectric coolant  28 . 
       FIG. 2  illustrates a plurality of self-contained liquid cooling modules  12  connected in series via a conduit  60  and forming a cooling system  100  for use in a hybrid vehicle or BEV. In one embodiment, the inlet  42  of the cooling element  38  for each module  12  is in fluid communication with the vehicle&#39;s air conditioning (A/C) system  120  by a conduit  70 . In turn, the heat generated from each cooling module  12  may be expelled through the outlet  44  to the coolant  130  by a conduit  80 . The coolant  130  provides an external heat exchange with the vehicle, where the vehicle is a hybrid vehicle. Alternatively, the heat generated from each cooling module  12  may be expelled through the outlet  44  and the conduit  80  to the coolant  130 , such as an electronic cooling loop, where the prime mover is a BEV, typically through a valve, such as a 3-way valve  140 . 
     The present disclosure further includes a method of cooling a vehicle battery pack. The method includes the steps of providing a closed and sealed container  14 . The container  14  has an interior space  16 . A battery assembly  18  is disposed within the interior space  16  of the container  14 . The battery assembly  18  includes a plurality of battery cells  20  having fluid channels  26  formed between the stacked cells  20 . The stacked cells  20  maintain a gap  24  between battery cells  20  of no greater than 0.50 mm and no less than 0.25 mm in one embodiment. In another embodiment, the gap  24  may be less than 0.25 mm. Each gap  24  forms the fluid channel  26  between adjacent battery cells  20 . A dielectric coolant  28  is disposed within the interior space  16  of the container  14 . The battery assembly  18  typically is fully immersed within the dielectric coolant  28  and the dielectric coolant  28  is received within the fluid channels  26 , completely contacting each of the battery cells  20 . By filling the gap  24  with the dielectric coolant  28 , both heating and cooling can be accomplished. 
     During start up of a vehicle, a heating element  34  located along the base area  36  of the container  14  may heat the dielectric fluid  28  to boiling. In one embodiment, the dielectric fluid  28  may be conditioned to have a boiling point at or near the desired operating temperature of the battery cells  20 . Vapors rise between the fluid channels  26 , heating the battery cells  20  to the operating temperature. Condensation heating ensures efficient and uniform temperature heat transfer without overshoot of the battery cell  20  temperatures. When the battery cells  20  are operating, the dielectric coolant  28  boils on the surfaces of the battery cell  20 , keeping temperatures of the surfaces uniform and transferring heat efficiently to the cooling element  38 . The heated coolant  28  rises, traveling through the fluid channels  26  from the base area  36  of the container  14  to the upper area  40 , fully flowing across each battery cell  20  throughout the interior space  16  of the container  14  as illustrated by arrows “A” and “B”. The cooled dielectric coolant  28  will return to the base area  36 , generally following either coolant paths “A” or “B.” Where the general location of the dielectric coolant  28  at the moment of boiling is located within the fluid channels  26  of the battery cells  20  in the center area and toward a side  50  of the battery cell stack  22 , the dielectric coolant  28  will tend to follow flow path “A”. Similarly, if the general location of the dielectric coolant  28  at the moment of boiling is located within the fluid channels  26  of the battery cells  20  in the center area and toward an opposing side  52  of the battery cell stack  22 , the dielectric coolant  28  will tend to follow flow path “B”. During operation, the coolant  28  flowing along the fluid channels  26  provides a substantially uniform surface temperature over each of the plurality of battery cells  20  while transferring heat away from each of the battery cells  20  by the flowing dielectric coolant  28 . 
     The step of condensing the vapors includes the use of the cooling element  38 , such as a chilled water plate, placed above the battery cells  20  in the upper area  40  of the container  14 . Multiple battery cells  20  form multiple modules  12 . The modules  12  are connected in series. The heated vapors rise to the upper area  40  of the container and are cooled by the cooling element  38 . The water within the cooling element  38  is chilled by an existing air conditioning system chiller of the vehicle and circulated from the inlet  42  to the outlet  44  of the cooling element  38 . A coolant temperature sensor  46  measures the dielectric coolant  28  temperature at the outlet  44  of the cooling element  38 . A coolant level sensor  48  measures the level of the dielectric coolant  28  within the container  14 . 
     While certain representative embodiments and details have been shown for purposes of illustrating the invention, it will be apparent to those skilled in the art that various changes may be made without departing from the scope of the disclosure, which is further described in the following appended claims.