Abstract:
A system and method of operating an automatic climate control system for a vehicle is disclosed. The method may include determining a breath level air temperature in a passenger compartment of the vehicle; determining a mean radiant temperature in the passenger compartment; determining an average air velocity in the passenger compartment; determining a clothing level factor, and calculating an equivalent homogeneous temperature based on the breath level air temperature, the mean radiant temperature, the average air velocity and the clothing level factor; comparing the calculated equivalent homogeneous temperature to a desired equivalent homogeneous temperature; and adjusting an output of the automatic climate control system based on the comparison of the calculated equivalent homogeneous temperature to the desired equivalent homogeneous temperature.

Description:
BACKGROUND OF INVENTION 
       [0001]    The present invention relates generally to automatic climate control systems for vehicles. 
         [0002]    A typical automotive vehicle with an automatic climate control system uses an in-car temperature sensor mounted in the instrument panel in combination with an ambient air temperature sensor and sometimes a solar load sensor as inputs to the automatic climate control system. The automatic climate control system then uses these inputs, along with a user defined desired temperature to determine the appropriate discharge air temperature, blower speed and the heating, ventilation and air conditioning (HVAC) mode. However, due to air stratification, heat storage in the instrument panel, and discharge from nearby HVAC vents, the accuracy of the temperature measurement from the in-car temperature sensor is degraded. In some vehicle tests, the temperature measured by the in-car temperature sensor may be as much as ten degrees Celsius different from the measured air temperature at a breath level (i.e., air temperature adjacent to the driver&#39;s face). Because of this drawback, calibration of the automatic climate control system for a new vehicle is relatively difficult and time consuming. 
         [0003]    To improve the temperature sensor measurement at breath level, some have employed ultrasonic temperature sensing. While this improves the temperature measurement at breath level, the thermal comfort of vehicle occupants involves more than just a temperature measurement. For example, radiant heat exchange, the distribution of air velocity, and occupant clothing level all also affect the occupant thermal comfort. 
       SUMMARY OF INVENTION 
       [0004]    An embodiment contemplates a method of operating an automatic climate control system for a vehicle, the method comprising the steps of: determining a breath level air temperature in a passenger compartment of the vehicle; determining a mean radiant temperature in the passenger compartment; calculating an equivalent homogeneous temperature based on the breath level air temperature and the mean radiant temperature; comparing the calculated equivalent homogeneous temperature to a desired equivalent homogeneous temperature; and adjusting an output of the automatic climate control system based on the comparison of the calculated equivalent homogeneous temperature to the desired equivalent homogeneous temperature. 
         [0005]    An embodiment contemplates a method of operating an automatic climate control system for a vehicle, the method comprising the steps of: determining a breath level air temperature in a passenger compartment of the vehicle; determining a mean radiant temperature in the passenger compartment; determining an average air velocity in the passenger compartment; determining a clothing level factor; calculating an equivalent homogeneous temperature based on an equation 
         [0000]    
       
         
           
             
               
                 T 
                 EHT 
               
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         [0000]    where T EHT  is the equivalent homogeneous temperature in degrees Celsius, T a  is the breath level air temperature in degrees Celsius, T r  is the mean radiant temperature in degrees Celsius, V a  is the average air velocity in meters per second and l clo  is the clothing level factor; comparing the calculated equivalent homogeneous temperature to a desired equivalent homogeneous temperature; and adjusting an output of the automatic climate control system based on the comparison of the calculated equivalent homogeneous temperature to the desired equivalent homogeneous temperature. 
         [0006]    An advantage of an embodiment is that a vehicle automatic climate control system employs a more complete control input and thermal comfort calculation for an automatic climate control system, resulting in better thermal comfort for a vehicle occupant. 
         [0007]    An advantage of an embodiment is that calibration time and costs may be reduced for the vehicle automatic climate control system employing the equivalent homogeneous temperature input as compared to a conventional automatic climate control system. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0008]      FIG. 1  is a schematic illustration of a vehicle and passengers according to a first embodiment. 
           [0009]      FIG. 2  is a schematic illustration of a vehicle and passengers according to a second embodiment. 
           [0010]      FIG. 3  is a schematic illustration of a portion of an automatic climate control system. 
       
    
    
     DETAILED DESCRIPTION 
       [0011]    Referring to  FIG. 1 , a portion of a vehicle, indicated generally at  20 , is shown. The vehicle  20  includes a passenger compartment  22  having a driver seat  24  for supporting a driver  26 , wearing clothing  27 , and a passenger seat  28  for supporting a passenger  30 . The passenger compartment  22  is enclosed partially by a roof  32 , a windshield  34 , a floor  36 , and doors  38  with windows. An instrument panel  40  is located in front of the driver seat  24 . A HVAC module  42 , which is part of an automatic climate control system  46 , is located behind, in, or under the instrument panel  40 . A HVAC controller  44  communicates with and controls the HVAC module  42  and may be located in or be separate from the HVAC module  42 . A blower  60  may be located in the HVAC module  42  to cause air flow through the module  42 . 
         [0012]    The automatic climate control system  46  also includes an infrared sensor  48  mounted to the roof  32 , for taking infrared measurements in front of the vehicle driver  26 , and ultrasonic temperature sensors  50 ,  52 , with a first sensor  50  mounted to the roof  32  and a second sensor  52  mounted on the instrument panel  40 . The ultrasonic temperature sensors  50 ,  52  work in conjunction to more accurately determine a temperature reading in front of the vehicle driver  26  than a conventional instrument panel mounted temperature sensor. A solar load sensor  54  may be mounted on the instrument panel  40  to measure an intensity and angle of solar load. An ambient air temperature sensor  56  may be employed to detect the ambient air temperature around the vehicle  20 . Also, an optional humidity sensor  58  may be employed. All of the sensors are in communication with the HVAC controller  44 . 
         [0013]      FIG. 2  illustrates a second embodiment. Since this embodiment is similar to the first, like reference numerals designate corresponding elements in the drawings, and to avoid unnecessary repetition the detailed description thereof will be omitted. Changed elements will be designated with a prime. With this embodiment, the ultrasonic temperature sensors  50 ′,  52 ′ are both mounted to the roof  32 . The other aspects of the automatic climate control system  46 ′ may remain unchanged, if so desired. 
         [0014]      FIG. 3  illustrates a portion of the automatic climate control system  46 ,  46 ′ of  FIGS. 1 and 2 . This portion of the automatic climate control system  46  will be discussed in view of  FIG. 1 , even though it is applicable to  FIG. 2  as well. The HVAC controller  44  includes inputs, indicated by the large arrows, a solar load sensor input  62 , a desired thermal comfort input  64 , and an equivalent homogeneous temperature (T EHT ) input  66 . The inputs are shown separate from the HVAC controller  44  for illustrative purposes and may in fact be integrated with the controller, which may take various forms of hardware and software that may be integrated or discrete components as is known to those skilled in the art. 
         [0015]    An optional input may be a humidity input  68 , received from the optional humidity sensor  58 . The relative humidity in the passenger compartment  22  generally has only a minor influence on occupant thermal comfort when its value is below 50%, so it may be employed or not, depending upon the particular vehicle application. 
         [0016]    The solar load sensor input  62  to the HVAC controller  44  accounts for the solar load on the driver  26  and passenger  30 . The solar load on occupants is dependent on glass properties, solar incidence angle, and incident solar spectrum, which are accounted for by the solar load sensor  54 . The solar load sensor  54  communicates with the HVAC controller  44  to create the solar load sensor input  62 . 
         [0017]    The desired thermal comfort input  64  is based on an occupant requested temperature input  70 , which may be a temperature setting made by the driver  26  on an HVAC control panel  72  (which is typically located on the vehicle instrument panel). An outside ambient temperature input  74 , as determined by the ambient temperature sensor  56  may also be employed. A look-up table  76  may be employed to determine a desired equivalent homogeneous temperature (T EHTD ), which is then communicated as the desired thermal comfort input  64  to the HVAC controller  44 . 
         [0018]    An equivalent homogeneous temperature is a measure of body heat loss producing a whole body thermal sensation that characterizes the highly non-uniform thermal environment of the vehicle passenger compartment  22 . Equivalent homogeneous temperature is a quantity that integrates the effects of breath level air temperature, air velocity and mean radiation to reflect an occupant body heat loss and thus accurately expresses combined thermal effects on an occupant in a single variable that accurately reflects occupant thermal comfort. 
         [0019]    The look-up table  76  shows an exemplary graph that employs empirical data to determine a desired T EHTD . A comfort rating  78  is used on the vertical axis and is based on empirical data relating to passenger thermal comfort, with 1 meaning that vehicle occupants feel cold, a 5 meaning occupants are thermally comfortable, up to a 9 where occupants feel hot. A first line  80  on the graph represents vehicle passenger compartment warming during cold ambient conditions, while a second line  82  represents vehicle passenger compartment cooling during hot ambient conditions. The discontinuity at the thermally comfortable level of 5 is due to the fact that people wear more clothing when the ambient temperature is cold and so feel thermally comfortable at a slightly cooler temperature in the passenger compartment  22 . The particular comfort rating  78  employed is merely exemplary and other empirical types of comfort ratings may be used in the look-up table instead, if so desired. 
         [0020]    The T EHT  input  66  is shown separate from the HVAC controller  44  for illustrative purposes, but the calculations to determine T EHT  may, in fact, take place inside of the controller  44 . The T EHT  input  66  is used as feedback in order to allow the HVAC controller  44  to make adjustments to the operation of the automatic climate control system so the desired thermal comfort of the driver  26  and passenger  30  can be attained. The following equations are employed to determine the value of T EHT : 
         [0000]    
       
         
           
             
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               EHT 
             
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         [0021]    where T a =a breath level air temperature in degrees Celsius, T r =a mean radiant temperature in degrees Celsius, l clo =a clothing level factor, and V a =an average air velocity around an occupant in meters per second (m/s). The thermal effect of the clothing level and air velocity magnitude tend to show up when the air velocity magnitude is greater than about 0.1 m/s, which is why the equation for calculating T EHT  can be made simpler when air velocities (V a ) are less than or equal to about 0.1 m/s. 
         [0022]    In order to calculate the T EHT  value from these equations, the thermal environmental factors around an occupant—the breath level air temperature (T a ), mean radiant temperature (T r ), air velocity around an occupant (V a ), and occupant clothing level factor (l clo )—are determined. 
         [0023]    The breath level air temperature (T a ) is an approximation of the dry bulb temperature of the air near an occupant&#39;s face. Accurate breath level air temperature (T a ) may be estimated based on ultrasonic sensing employing output from the ultrasonic sensors  50 ,  52 . 
         [0024]    The mean radiant temperature (T r ) is the uniform surface temperature of an imaginary enclosure in which an occupant would exchange the same amount of radiant heat as in the actual non-uniform space. The output from the infrared sensor  48  provides the mean radiant temperature of the interior surfaces in the field of view of the sensor  48 . Thus, a wide field of view infrared sensor is preferred in order to cover most of the surfaces in front of an occupant. 
         [0025]    The magnitude of the air velocity around an occupant (V a ) influences convective heat transfer. The air velocity around an occupant (V a ) is correlated with the total automatic climate control system air flow rate, which is based on the speed of the blower  60  and the particular HVAC mode (e.g., defrost, floor or chest vents) being employed. The particular correlation of blower speed and HVAC mode to air velocity around an occupant (V a ) is determined empirically, and depends upon the particular vehicle passenger compartment geometry and vent locations. 
         [0026]    A typical clothing level factor (l clo ) in hot ambient conditions is about 0.5 and the clothing level factor (l clo ) in cold ambient conditions is about 1.0. These produce relatively accurate results for meeting occupant thermal comfort requirements. More specific clothing level factors (l clo ) can be introduced as a calibration parameter to the automatic climate control system  46 , if so desired. 
         [0027]    Having received various inputs  62 ,  64 ,  66 ,  68 , the HVAC controller  44  determines the needed output to achieve the desired thermal comfort of the occupant. The HVAC controller  44  may then output a desired discharge air temperature, a desired HVAC blower speed and a HVAC mode needed to achieve occupant thermal comfort. 
         [0028]    While certain embodiments of the present invention have been described in detail, those familiar with the art to which this invention relates will recognize various alternative designs and embodiments for practicing the invention as defined by the following claims.