Abstract:
A method of controlling the ventilation system for an energy source in a fuel cell vehicle is disclosed, which includes an HVAC system, a fluid reserve, and a rechargeable energy storage system (RESS), capable of controlling a temperature of the RESS to militate against damage to or a shortened life of the battery, while maximizing vehicle durability, efficiency, performance, and passenger comfort.

Description:
FIELD OF THE INVENTION 
     The present disclosure relates to a method of operation of a fuel cell system. More particularly, the invention relates to a control of a ventilation system in a rechargeable energy storage system in a vehicle. 
     BACKGROUND OF THE INVENTION 
     Various hybrid vehicles have been designed and developed in the automotive industry that operate using fuel cell technology and other rechargeable energy storage and generating systems. In a typical fuel cell vehicle, a fuel cell generates electricity through an electrochemical reaction between hydrogen and oxygen to charge batteries or to provide power for an electric motor. In certain fuel cell vehicles, the vehicle requirements allow a higher power split between a battery system and a fuel cell system. In other words, the fuel cell system is the main energy source having a greater ratio of use than the battery system. The battery system covers peak loads, for example during acceleration, smoothens the fuel cell system load profile to enhance fuel cell system durability, and provides high voltage power in situations where the fuel cell system is not capable of producing power itself such as during startup and shutdown, for example. To support the fuel cell system in these vehicles, the vehicles are equipped with a high power density battery system. 
     The fuel cell vehicles equipped with the high power density battery system require a ventilation system for the battery system to control a temperature and maintain a performance of the battery cells. Performance of the battery cells is required for full vehicle performance including maximum acceleration and regeneration of kinetic energy during braking. The ventilation system for the battery system is separate from a cooling device controlling a temperature of the fuel cell system, as the temperature set points of the battery system and the fuel cell system are different. 
     Typically, the ventilation system includes a ventilator fan and a housing, and draws air from the passenger compartment of the vehicle. The air flows through a conduit to the battery system. However, passengers are exposed to noise generated by the ventilator fan and to the air being drawn into the conduit. Moreover, the extraction of air from the passenger compartment by the ventilation system may disrupt circulation of air in the passenger compartment, making it uncomfortable for the passengers in close proximity to the opening. Further, if the mass flow of the air drawn into the ventilation system is greater than the mass flow of the air being emitted by the HVAC system, the air may be drawn back through at least one HVAC system emission outlet into the passenger compartment to equalize the pressure in the passenger compartment, or, if a check valve is installed in the HVAC system emission outlets, the passenger compartment may become under-pressurized creating an uncomfortable environment for the passengers. 
     U.S. Pat. No. 6,978,855 discloses a cooling system for an electricity storing device in a fuel cell vehicle. The cooling system consists of a plurality of holes formed in the floor of the passenger compartment of the vehicle and a fan. The through holes are provided as inlet ports and outlet ports for a housing of the electricity storing device. The fan is disposed adjacent the inlet ports as a means for discharging air within the housing of the electricity storing device. Air flows into the housing through the inlet ports from the passenger compartment to cool the electricity storing device and is then discharged through the outlet ports into a space under a rear seat in the passenger compartment. Although the outlet ports are disposed at angles to prevent discharged air from directly entering the inlet ports, a temperature of the air drawn into the cooling system is influenced by the discharged air, making the cooling system less efficient. Further, the plurality of holes formed in the floor of the passenger compartment expose the passengers in the passenger compartment to the noise generated by the fan and the air discharged from the housing, thereby decreasing passenger comfort and perceived vehicle quality. 
     It would be desirable to develop a method for controlling ventilation of a rechargeable energy storage system (RESS) in a fuel cell vehicle, which prevents damage to or a shortened life of the energy storage device, while maximizing durability, efficiency, performance, and passenger comfort. 
     SUMMARY OF THE INVENTION 
     In concordance and agreement with the present invention, a method for controlling ventilation of a rechargeable energy storage system (RESS) in a fuel cell vehicle is disclosed, which prevents damage to or a shortened life of the energy storage device, while maximizing durability, efficiency, performance, and passenger comfort. 
     In one embodiment, the method for controlling the ventilation of a rechargeable energy storage system (RESS) in a vehicle comprises the steps of: providing a ventilation system having an HVAC system in fluid communication with a fluid reserve, and the fluid reserve in fluid communication with the RESS; determining the maximum noise output level of at least one vehicle component; determining the ventilation requirement of the RESS; and controlling the flow rate of a fluid through a fluid transfer device for conveying the fluid from the reserve to the RESS as a function of the maximum noise output level and the ventilation requirement of the RESS. 
     In another embodiment, the method for controlling the ventilation of a rechargeable energy storage system (RESS) in a vehicle comprises the steps of: providing a ventilation system having an HVAC system in fluid communication with a fluid reserve, and the fluid reserve in fluid communication with the RESS; determining the maximum noise output level of at least one vehicle component; determining the ventilation requirement of the RESS; controlling the flow rate of a fluid through a fluid transfer device for conveying the fluid from the reserve to the RESS as a function of the maximum noise output level and the ventilation requirement of the RESS; and regulating the flow rate of the HVAC system according to the flow rate of the fluid through the fluid transfer device. 
     In another embodiment, a system for controlling the ventilation of a rechargeable energy storage system (RESS) in a vehicle comprises: a maximum noise output calculating unit in electrical communication with at least one vehicle component; and a fluid transfer device control unit in electrical communication with the maximum noise output calculating unit and the RESS. 
    
    
     
       DRAWINGS 
       The above, as well as other advantages of the present invention, will become readily apparent to those skilled in the art from the following detailed description of an exemplary embodiment when considered in the light of the accompanying drawings in which: 
         FIG. 1  is a schematic flow diagram of a ventilation system in a fuel cell vehicle according to an embodiment of the invention; 
         FIG. 2  is a schematic diagram of a control system for the ventilation system illustrated in  FIG. 1 ; and 
         FIG. 3  is a schematic diagram of a control system for the ventilation system illustrated in  FIG. 1  according to another embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The following detailed description and appended drawings describe and illustrate various exemplary embodiments of the present invention. The description and drawings 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. It is understood that materials other than those described can be used without departing from the scope and spirit of the invention. In respect of the methods disclosed, the steps presented are exemplary in nature, and thus, are not necessary or critical. 
       FIG. 1  illustrates a ventilation system  8  for an energy storage device  40  in a fuel cell vehicle (not shown) according to an embodiment of the invention. The ventilation system  8  includes a heating, ventilation, and air conditioning (HVAC) system  10  which provides a conditioned fluid, a reserve  12  which contains the conditioned fluid, and a rechargeable energy storage system (RESS)  24  which uses the conditioned fluid as a coolant. 
     The HVAC system  10  includes a fan  16 , an evaporator  18 , and a heater  20 . The fan  16  causes the flow of a desired ratio of ambient fluid and fluid recirculated (not shown) from the reserve  12  through the evaporator  18 . In the embodiment shown, the fluid is air. However, other fluids can be used as desired. 
     The evaporator  18  cools the fluid traveling though the evaporator  18  in a manner commonly known in the art. The temperature of the fluid is typically lowered from approximately 25 degrees Celsius to 15 degrees Celsius, although it is understood that the temperature can be changed to other values as well. 
     The fluid may also be heated before exiting the HVAC system  10 . In these situations, a portion of the fluid exiting the evaporator  18  is directed to a heater  20  by a bypass switch  22 . The bypass switch  22  may be a valve or a moveable door, for example. The bypass switch  22  causes a portion of the fluid exiting the evaporator  18  to flow directly to the reserve  12  and the remaining portion of the fluid to flow into the heater  20 . The heater  20  increases the temperature of the fluid traveling through the heater  20  in a manner commonly known in the art. After exiting the heater  20 , the fluid mixes with the fluid flowing directly from the evaporator  18 . If any of the fluid entering the HVAC system  10  passes through the heater  20 , the temperature of the mixed fluid is increased. Typically, the temperature is raised between 15 degrees Celsius and 20 degrees Celsius, although it is understood that the temperature of the mixed fluid can be raised to other temperatures as desired. The conditioned fluid is then exhausted into the reserve  12 . 
     According to the illustrated embodiment of the invention, the reserve  12  is the passenger compartment of the fuel cell vehicle. The reserve  12  is disposed between the HVAC system  10  and the RESS  24  and is in fluid communication with the HVAC system  10  and a ventilator  14 . The reserve  12  is also in fluid communication with the atmosphere. 
     The RESS  24  includes the ventilator  14  and a battery system  32 . The ventilator  14  is disposed between the reserve  12  and the battery system  32 . The ventilator  14  includes a hollow housing  34  and a fluid transfer device  36 . The housing  34  is adapted to enclose the fluid transfer device  36  and includes an inlet  30  formed therein in fluid communication with the reserve  12 . Any conventional material can be used to form the housing  34  such as polypropylene, for example. In the embodiment shown, the fluid transfer device  36  is an adjustable speed fan. However, it is understood that the fluid transfer device  36  can be any transfer device known in the art, such as a pump or a turbine, for example. The fluid transfer device  36  causes fluid to flow from the reserve  12  to the RESS  24 . 
     The battery system  32  includes a housing  38  having a hollow interior and at least one energy storage device  40 . The housing  38  is adapted to contain the energy storage device  40  and includes an outlet  42  formed therein. Any conventional material can be used to form the housing  38  such as polypropylene, for example. In the embodiment shown, the energy storage device  40  is a lithium battery cell. It is understood that the energy storage device  40  can be any energy storage device know in the art such as an accumulator, a super-capacitor or combinations thereof, for example. Typically, the temperature of the fluid entering the battery system  32  is lower than a temperature of the fluid exhausted from the battery system  32 . The temperature of the fluid entering the battery system  32  is typically approximately 20 degrees Celsius. However, the temperature of the fluid can be any temperature, as desired. The battery system  32  is in fluid communication with the ventilator  14 . 
     In  FIG. 2 , a control system  43  for controlling the ventilation of the RESS  24  is shown. The control system  43  includes a maximum noise output calculating unit  44 , a fluid transfer device control unit  46 , and a fluid transfer device restrictor  48 . The noise output calculating unit  44  is in electrical communication with the RESS  24 , a fuel cell system compressor (not shown), a fuel cell vehicle radio (not shown), and the fluid transfer device control unit  46 . The fluid transfer device control unit  46  is in electrical communication with the noise output calculating unit  44 , the RESS  24 , and the fluid transfer device restrictor  48 . The fluid transfer device restrictor  48  is in electrical communication with the fluid transfer device control unit  46 , the HVAC system  10 , and the fluid transfer device  36 . 
     The noise output calculating unit  44  calculates the maximum noise output level of at least one fuel cell vehicle component or vehicle state. The noise output calculating unit  44  calculates the maximum noise level by looking up and summing values from pre-formulated tables for separate fuel cell vehicle components and vehicle states. In this embodiment, the maximum noise output level is calculated based on the noise output values found in tables  45   a ,  45   b ,  45   c  associated with a RESS power level  50 , a fuel cell system compressor power level  54 , and a radio volume  58 , respectively. The RESS power level  50  is associated with RESS utilization during energy storage regeneration and energy distribution to at least one vehicle system. The compressor power level  54  is associated with the demands of providing oxygen molecules to the fuel cell stack. It is understood that the maximum noise output level may be calculated from pre-formulated tables associated with vehicle components including a radio or from vehicle states, for example an HVAC flow rate, vehicle wheels, ram fluid, or a passenger compartment window position (open/closed), as desired. The maximum noise output level is then used by the fluid transfer device control unit  46  to determine a maximum allowable flow rate of the fluid transfer device  36 . 
     The fluid transfer device control unit  46  calculates the maximum allowable flow rate based on the ventilation requirement  62  of the battery system  32 , the noise output of the fluid transfer device  36  associated with the ventilation requirement  62 , and the maximum noise output level calculated by the noise output calculating unit  44 . The ventilation requirement  62  is derived from the temperature of the RESS  64  and a desired temperature of the RESS  66 . The maximum allowable flow rate of the fluid transfer device  36  is electronically communicated to the fluid transfer restrictor  48 . 
     In situations where the flow rate of the fluid transfer device  36  exceeds the HVAC flow rate  72 , the fluid transfer device restrictor  48  limits the flow rate of the fluid transfer device  36  to that of the HVAC flow rate  72  by transmitting a signal  70  corresponding to the HVAC flow rate  72  to the fluid transfer device  36 . The maximum allowable flow rate of the fluid transfer device  36  is found by looking up the corresponding value of the HVAC flow rate  72  in a lookup table  73 . The limitation of the flow rate of the fluid transfer device  36  to that of the HVAC flow rate  72  militates against an under-pressurization of the reserve  12  caused by fluid being drawn from the reserve  12  by the ventilator  14  at a rate greater than the rate of fluid being exhausted into the reserve  12  by the HVAC system  10 . 
       FIG. 3  depicts a control system  43 ′ for controlling the ventilation of the RESS  24  according to another embodiment of the invention. Reference numerals for similar structure in respect of the discussion of  FIG. 2  above are repeated with a prime (′) symbol. The control system includes a maximum noise output calculating unit  44 ′ and a fluid transfer device control unit  46 ′. The noise output calculating unit  44 ′ is in electrical communication with the RESS  24 ′, a fuel cell system compressor (not shown), a fuel cell vehicle radio (not shown), and the fluid transfer device control unit  46 ′. The fluid transfer device control unit  46 ′ is in electrical communication with the RESS  24 ′, the fluid transfer device  36 ′, and the HVAC system  10 ′. 
     The noise output calculating unit  44 ′ calculates the maximum noise output level of at least one vehicle component or vehicle state. The noise output calculating unit  44 ′ calculates the maximum noise level by looking up and summing values from pre-formulated tables for separate fuel cell vehicle components and vehicle states. In this embodiment, the maximum noise output level is calculated based on the noise output values found in tables  45   a ′,  45   b ′,  45   c ′ associated with a RESS power level  50 ′, a fuel cell system compressor power level  54 ′, and a radio volume  58 ′, respectively. The RESS power level  50 ′ is associated with RESS utilization during energy storage regeneration and energy distribution to at least one vehicle system. The compressor power level  54 ′ is associated with the demands of providing oxygen molecules to the fuel cell stack. It is understood that the maximum noise output level may be calculated from pre-formulated tables associated with vehicle components including a radio or from vehicle states, for example an HVAC flow rate, vehicle wheels, ram fluid, or a passenger compartment window position (open/closed), as desired. The maximum noise output level is then used by the fluid transfer device control unit  46 ′ to determine the maximum allowable flow rate of the fluid transfer device  36 ′. 
     The fluid transfer device control unit  46 ′ calculates the maximum allowable flow rate based on the ventilation requirement  62 ′ of the battery system  32 ′, the noise output of the fluid transfer device  36 ′ associated with the ventilation requirement  62 ′, and the maximum noise output level calculated by the noise output calculating unit  44 ′. The ventilation requirement  62 ′ is derived from the temperature of the RESS  64 ′ and a desired temperature of the RESS  66 ′. The maximum allowable flow rate of the fluid transfer device  36 ′ is electronically communicated to the fluid transfer device  36 ′ and the HVAC system  10 ′. 
     Instead of utilizing a fluid transfer device restrictor  48  as shown in  FIG. 2  to militate against under-pressurization of the reserve  12 , the control system  43 ′ controls the required HVAC flow rate  78  which meets or exceeds the allowable flow rate of the fluid transfer device  36 ′. The required HVAC flow rate  78  is found from a lookup table  79  based on the allowable flow rate of the fluid transfer device  36 ′. The allowable flow rate of the fluid transfer device  36 ′ is electronically communicated by the fluid transfer device control unit  46 ′ transmitting a first signal  70 ′ to the fluid transfer device  36 ′ and a second signal  76  to the HVAC system  10 ′. 
     In operation, the system for controlling the ventilation of the RESS  24  can be used to conceal the noise output of the fluid transfer device or to provide acoustic feedback to the passenger that the RESS  24  is storing energy during regeneration mode or delivering energy to a vehicle system. The maximum noise output level is directly proportional to the RESS power level  50 ,  50 ′ and at least one vehicle component or vehicle state. Typically, the noise output of the fluid transfer device  36 , is concealed by the noise output of at least one vehicle component or vehicle state. However, during demanding vehicle performance where the RESS  24  utilization and the battery system  32  ventilation requirements are above normal operating levels, the maximum noise output level increases in proportion to the RESS power level  50 ,  50 ′. As a result, the noise output of the fluid transfer device  36  may exceed the noise output of the other vehicle components or vehicles states and therefore provide acoustic feedback to the passenger. 
     From the foregoing description, one ordinarily skilled in the art can easily ascertain the essential characteristics of this invention and, without departing from the spirit and scope thereof, make various changes and modifications to the invention to adapt it to various usages and conditions.