Abstract:
A method of controlling a temperature of a battery is disclosed. The method includes providing a thermoelectric device in thermally-conductive contact with the battery, measuring an actual temperature of the battery, comparing the actual temperature of the battery to a reference temperature for the battery, heating the battery by operation of the thermoelectric device when the actual temperature is less than the reference temperature and cooling the battery by operation of the thermoelectric device when the actual temperature exceeds the reference temperature.

Description:
[0001]     This application claims the benefit of U.S. Provisional Application Ser. No. 60/590,879 filed Jul. 23, 2004. 
     
    
     FIELD OF THE INVENTION  
       [0002]     The present invention relates to thermoelectric devices which utilize electrical power to generate a thermal gradient. More particularly, the present invention relates to methods of controlling the temperature of batteries by using thermoelectric devices to cool or heat the batteries, as needed.  
       BACKGROUND OF THE INVENTION  
       [0003]     Thermoelectric (TE) technology has attracted worldwide interest in recent years. TE devices can be used for cooling and electrical power generation purposes in a variety of applications. While much of the work in thermoelectric technology has focused on the development of new thermoelectric materials, incorporation of the newly-developed materials into TE devices and practical application of the TE devices in automotive and other applications is also being investigated.  
         [0004]     Batteries, including those used in automotive applications, are characterized by optimum operational temperature windows. During operation, high battery temperatures due to consecutive charge-discharge cycles, hot weather, engine heat, etc., are common. This results in a short battery lifespan and degraded battery performance. On the other hand, low battery temperatures encountered during cold startup conditions in cold weather, for example, prohibit efficient battery operation due to increased internal electrical resistance.  
         [0005]     Thermoelectric technology includes heating and cooling capabilities of TE devices. The basis of such heating and cooling capabilities is the Peltier effect, which is expressed using a Peltier circuit. A Peltier circuit is a TE device which includes two thermally-opposite sides. When an electrical current is applied to the Peltier circuit in one direction, one side of the TE device creates heat, and therefore, has heating capability while the other side absorbs heat, and therefore, has cooling capability. Reversing the polarity of the electrical current applied to the Peltier circuit creates the opposite effect.  
         [0006]     Accordingly, a control scheme or method is needed which utilizes a TE device to cool or heat a battery, as required, using the Peltier effect.  
       SUMMARY OF THE INVENTION  
       [0007]     The present invention is generally directed to thermoelectric methods which are suitable to control the temperature of batteries in a variety of applications. The methods include providing a thermoelectric device; providing a battery in thermally-conductive contact with the thermoelectric device; measuring a temperature of the battery; comparing the measured temperature of the battery to a desired reference temperature; and heating or cooling the battery, as necessary, using the Peltier effect by transmitting a current through the thermoelectric device in an appropriate direction. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0008]     The invention will now be described, by way of example, with reference to the accompanying drawings, in which:  
         [0009]      FIG. 1  is a schematic of a battery temperature control scheme according to the present invention;  
         [0010]      FIG. 2  is a schematic of a battery temperature control scheme according to an alternative embodiment of the present invention; and  
         [0011]      FIG. 3  is a schematic of a battery temperature control scheme according to still another embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0012]     Referring initially to  FIG. 1 , an illustrative embodiment of a thermoelectric (TE) battery control system, hereinafter system, according to the present invention is generally indicated by reference numeral  10 . The system  10  includes a thermoelectric (TE) device  12  having a conventional Peltier circuit (not shown). Responsive to flow of electrical current in one direction through the Peltier circuit, heat is generated at one side and absorbed at the opposite side of the TE device  12 . When current flows in the opposite direction through the Peltier circuit, the hot and cold sides of the TE device  12  are reversed.  
         [0013]     A battery  38 , such as an automotive battery, for example, is provided in thermally-conductive contact with one side of the TE device  12 . The battery  38  may be any type of battery including but not limited to a lead acid battery, a nickel metal hydride battery or a lithium ion battery. Furthermore, the TE device  12  can be arranged in any desired configuration with respect to the battery  38 . For example, the TE device  12  can be built into the battery assembly for the battery  38  or can form an enclosure surrounding the battery  38 .  
         [0014]     The system  10  further includes a controller  14 , which may be a proportional/integral/derivative (PID) controller, for example. The controller  14  should be stable to environmental disturbances  36 , such as heat losses and inflows, from the environment. The controller  14  may be any type of controller which is capable of changing the direction of electrical current through the Peltier circuit of the TE device  12  in order to heat or cool the battery  38  depending on a measured temperature of the battery  38 , as will be hereinafter further described.  
         [0015]     The controller  14  may include a temperature sensor  20  which is provided in thermally-conductive contact with the battery  38 . The temperature sensor  20  measures the temperature of the battery  38  based on the reception of heat  34  from the battery  38 . A comparator  18 , the purpose of which will be hereinafter described, is connected to the temperature sensor  20 . The temperature sensor  20  includes the capability to transmit an actual temperature transmission signal  28 , which corresponds to the measured temperature (T) of the battery  38 , to the comparator  18 .  
         [0016]     The controller  14  typically further includes a reference temperature database  16  into which reference temperature input  24  corresponding to a desired or reference temperature for the battery  38  may be programmed. The reference temperature (T ref ) for the battery  38  is the temperature which is required for optimum performance and durability of the battery  38 . The reference temperature database  16  includes the capability to transmit a reference temperature transmission signal  26  to the comparator  18 .  
         [0017]     The comparator  18  is provided with the capability to compare the reference temperature (T ref ), received from the reference temperature database  16  via the reference temperature transmission signal  26 , to the actual temperature (T) of the battery  38 , received from the temperature sensor  20  via the actual temperature transmission signal  28 , by calculating the temperature difference (e) according to the equation: 
 
 e=T−T   ref . 
 
 An actuator  22  is connected to the comparator  18  to receive a comparator output signal  30 , which corresponds to the value of e, from the comparator  18 . The actuator  22  is, in turn, connected to the TE device  12  to control the direction of current through the Peltier circuit in the TE device  12 , via a control input signal  32 , depending on the value of e. 
 
         [0018]     In operation of the system  10 , the reference temperature (T ref ) input  24 , corresponding to the desired operational temperature for the battery  38 , is initially programmed into the reference temperature database  16 . During operation of the battery  38 , the temperature sensor  20  continually measures the actual temperature (T) of the battery  38  responsive to input of heat  34  from the battery  34 . The temperature sensor  20  transmits the actual temperature transmission signal  28 , corresponding to the measured temperature (T) of the battery  38 , to the comparator  18 . Simultaneously, the reference temperature database  16  transmits the reference temperature transmission signal  26 , corresponding to the reference temperature (T ref ), to the comparator  18 .  
         [0019]     The comparator  18  calculates the value of e by subtracting the value of T ref  from the value of T. Thus, in the event that T is higher than T ref , e will have a positive value. This indicates an excessively high operational temperature of the battery  38 . Therefore, the comparator  18  transmits the comparator output signal  30 , which indicates the positive value of e, to the actuator  22 . The actuator  22 , in turn, causes flow of current through the Peltier circuit of the TE device  12  in a first direction to facilitate cooling of the battery  38 , via the control input signal  32 . Therefore, the value of T drops as the calculated value of e drops and approaches or reaches zero. At that point, the actuator  22 , responsive to feedback control by the comparator  18  as facilitated by the temperature sensor  20  via the actual temperature transmission signal  28 , terminates flow of current through the Peltier circuit of the TE device  12  in order to prevent further cooling of the battery  38  and maintain the value of T as close as possible to the value of T ref . This ensures that the battery  38  operates at or near T ref  for optimum performance, reliability and duration of the battery  38 .  
         [0020]     In the event that T is lower than T ref , the value of e as calculated by the comparator  18  will have a negative value. This indicates an excessively low operational temperature of the battery  38 , as may be the case, for example, upon initial start-up of an automobile or during operation of the battery  38  in cold weather. In that case, the comparator  18  transmits the comparator output signal  30 , which now indicates the negative value of e, to the actuator  22 . Via the control input signal  32 , the actuator  22 , in turn, causes flow of current through the Peltier circuit of the TE device  12  in a second direction in order to facilitate heating of the battery  38 . Therefore, T rises and approaches or reaches T ref  as the calculated value of e rises and approaches or reaches zero. At that point, the actuator  22 , responsive to feedback control by the comparator  18  and the temperature sensor  20 , terminates flow of current through the Peltier circuit of the TE device  12  in order to maintain the value of T as close as possible to the value of T ref .  
         [0021]     Referring next to  FIG. 2 , another illustrative embodiment of a thermoelectric (TE) battery control system, hereinafter system, of the present invention is generally indicated by reference numeral  40 . The system  40  includes a thermoelectric (TE) device  42  which includes a conventional Peltier circuit (not shown). A battery  52 , such as an automotive battery, for example, is disposed in thermally-conductive contact with one side of the TE device  42  typically through a thermal interface  54 . The thermal interface  54  may be any suitable thermally-conductive material. Cooling fins  44  may be provided in thermally-conductive contact with the other side of the TE device  42 .  
         [0022]     The battery  52  may be contained inside a thermal enclosure  48 , which may be any suitable thermally-insulating material. The thermal enclosure  48  serves to thermally insulate the battery  52  from environmental heat during operation. One or multiple controllable heat vents  50  may be provided in the thermal enclosure  48  to either retain heat in the thermal enclosure  48  or dissipate excessive heat from the battery  52  depending on the thermal requirements of the battery  52 . A temperature sensor  53  is typically provided in thermal contact with the battery  52 .  
         [0023]     A battery temperature control unit  46  is connected to the temperature sensor  53 . The temperature sensor  53  includes the capability to transmit temperature transmission signals  58 , which correspond to a measured temperature of the battery  52 , to the battery temperature control unit  46 . The battery temperature control unit  46  may be connected to the heat vent or vents  50  to control the position of the vent or vents  50 , via a vent control signal  60 , depending on the measured temperature of the battery  52 , as will be hereinafter described. The battery temperature control unit  46  is further connected to the TE device  42  to control the direction of current flow through the Peltier circuit, and therefore, facilitate heating or cooling of the battery  52 , via TE device control signals  56 , depending on the measured temperature of the battery  52 . The battery temperature control unit  46  may be designed and programmed to utilize the same method as that heretofore described with respect to the temperature sensor  20 , reference temperature database  16 , comparator  18  and actuator  22  of the system  10  shown in  FIG. 1  in order to determine and effect the heating and cooling requirements of the battery  52 .  
         [0024]     In operation of the system  40 , a reference temperature which corresponds to the optimum operating temperature of the battery  52  is initially programmed into the battery temperature control unit  46 . During operation of the battery  52 , the temperature sensor  53  continually measures the temperature of the battery  52  and transmits this information, in the form of the temperature transmission signal  58 , to the battery temperature control unit  46 . In the event that the measured temperature of the battery  52  is higher than the reference temperature, the battery temperature control unit  46 , via the TE device control signal  56 , induces flow of current in a first direction through the Peltier circuit of the TE device  42 . This causes cooling of the battery  52  in order to lower the measured temperature of the battery  52  to or near the reference temperature. Additionally, the battery temperature control unit  46 , via the vent control signal  60 , may facilitate opening of the vent or vents  50  to dissipate additional heat from the battery  52 . As the TE device  42  cools the battery  52 , the cooling fins  44  dissipate heat from the hot side of the TE device  42 . This increases the battery-cooling efficiency of the TE device  42 .  
         [0025]     In the event that the measured temperature of the battery  52  is lower than the reference temperature, as may be the case during start-up of an automobile or during operation of the battery  52  in cold weather, for example, the battery temperature control unit  46 , via the TE device control signal  56 , induces flow of current in a second direction through the Peltier circuit of the TE device  42 . Consequently, the temperature of the battery  52  rises and approaches or reaches the reference temperature. The battery temperature control unit  46 , via the vent control signal  60 , may additionally facilitate closing of the vent or vents  50  to retain heat in the thermal enclosure  48  and raise the temperature of the battery  52 .  
         [0026]     Referring next to  FIG. 3 , another illustrative embodiment of the TE battery control system, hereinafter system, of the present invention is generally indicated by reference numeral  70 . The system  70  is similar in design to the system  40  heretofore described with respect to  FIG. 2 , except multiple heat-conductive strips  72  are packaged into the battery  52 . The heat-conductive strips  72  may be suitable thermally-conductive material and facilitate efficient temperature control during operation of the battery  52  and system  70 .  
         [0027]     While the preferred embodiments of the invention have been described above, it will be recognized and understood that various modifications can be made in the invention and the appended claims are intended to cover all such modifications which may fall within the spirit and scope of the invention.