Abstract:
A method of controlling a vehicle heating, ventilation, and air conditioning (HVAC) system. Outside or ambient temperature, evaporator temperature, and coolant temperature are measured with sensors. These values, along with a TAO, which is a calculated value of outlet temperature in the vehicle, are sent to a controller. The controller determines a predicted heater core outlet temperature based upon the coolant temperature. Based upon the outside air temperature and coolant temperature, the controller will decide whether to use the previously determined estimated heater core outlet temperature or to substitute an alternate value for the heater core outlet temperature to determine a position for the air mix door. After calculating the air mix door position, the controller signals an air mix door movement device to adjust the air mix door to the required position. Position of the air mix door affects the air temperature inside of the vehicle.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention is directed toward a method for controlling a vehicle heating, ventilation, and air conditioning (HVAC) system. 
   2. Description of Related Art 
   In modern vehicles it is common to have an HVAC system for an occupant compartment (hereinafter “cabin”). The HVAC system provides warm and cool air to the cabin of the vehicle. Further, an HVAC control system allows occupants to select a set temperature for the cabin. Once the set temperature is selected, the HVAC control system provides conditioned air to adjust the climate of the cabin. 
   The conditioned air that is heated is typically provided to the cabin by passing outside air through a heater core before being discharged into the cabin. The conditioned air that is cooled is typically provided to the cabin by passing outside air through an evaporator before being discharged into the cabin. Many times, the HVAC control system includes a controller that automatically makes adjustments, based upon the set temperature, to raise or lower the temperature of the conditioned air. 
   For example, the position of an air mix door determines the amount of air that can flow through the heater core. The more air that flows through the heater core, the warmer the air in the cabin will become. Typically, the position of the air mix door is controlled by the controller. Usually, the controller determines the position of the air mix door by a calculation that includes several variables. For example, the temperature of the evaporator and the calculated outlet temperature are used in the calculation. Further, a predicted temperature of air leaving the heater core, which is based upon engine coolant temperature, is used. 
   However, it has been found that during cold outside air temperatures, the calculation used to determine the position of the air mix door and the related subsequent control of the air mix door, results in an under-heating of the cabin. It can be appreciated that this under-heating of the cabin is undesirable. 
   Therefore, there exists a need in the art for a method to better control the HVAC system so as to provide conditioned air that will properly adjust the cabin air to maximize occupant comfort. 
   SUMMARY OF THE INVENTION 
   The present invention is directed toward an HVAC system that more accurately controls a position of the air mix door when outside temperature is low and engine coolant is warm. 
   More specifically, the present invention relates to controlling an HVAC system for a vehicle cabin, the system including a controller, a coolant temperature sensor, an evaporator temperature sensor, and an ambient air temperature sensor. The coolant and evaporator temperature sensors measure the temperature of engine coolant and of an evaporator, respectively. The ambient air temperature sensor measures the outside air temperature (T am ). A predicted heater core outlet temperature (T h ) is based upon the engine coolant temperature (T w ). Depending on the outside air temperature (T am ) and the engine coolant temperature (T w ), the controller substitutes an alternate heater core outlet temperature (T h ′) for the predicted heater core temperature (T h ) when calculating an air mix door position (SW %). More specifically, when the outside air temperature (T am ) is low and the coolant temperature (T w ) is warm, the controller uses the alternate heater core outlet temperature (T h ′), which is typically smaller in magnitude than the predicted heater core temperature (T h ). By utilizing the alternate heater core outlet temperature (T h ′) when the outside air temperature (T am ) is low and the coolant temperature (T w ) is warm, a more accurate estimate of the temperature of the air leaving the heater core is realized. This more accurate estimate ensures that the air mix door is positioned so as to allow the proper amount of heated air into the cabin, thereby ensuring that the cabin is not under-heated. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     These and further features of the invention will be apparent with reference to the following description and drawings, wherein: 
       FIG. 1  is a side view of a vehicle with an HVAC control system of the present invention; 
       FIG. 2  is an perspective view of an interior of the vehicle of  FIG. 1 ; 
       FIG. 3  is a schematic diagram illustrating the relationship between various components of the HVAC control system; and 
       FIG. 4  is a flowchart illustrating a method according to the present invention. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   With reference to  FIGS. 1-3 , an HVAC control system  10  for use in a vehicle  12  according to the present invention is shown. The vehicle  12  includes a cabin  14  bounded by a floor  16 , a roof  18 , doors (not shown), an engine compartment area  20 , and a storage area  22 . An engine  24 , a radiator  26 , a radiator fan  28 , a coolant pump  30 , and several parts of an HVAC system  32  are disposed in the engine compartment  20 . Inside of the engine  24  are a supply passageway  34  and a discharge passageway  36 , each for containing engine coolant. A variety of hoses, such as a first supply hose  38 , a second supply hose  40 , a discharge hose  42 , a heater core supply hose  44 , and a heater core discharge hose  46  allow coolant to circulate. The HVAC system  32  includes an air mix door  48 , a compressor, a condenser, ducts  50 , a dryer, an evaporator  52 , an evaporator fan  54 , an expansion valve, a heater core  56 , and outlets  58 , as is well known in the art. The compressor, the condenser, the dryer, the evaporator  52 , and the expansion valve are responsible for cooling the air, while the heater core  56  is responsible for warming the air. Additionally, the air mix door  48 , the ducts  50 , the evaporator fan  54 , and the outlets  58  ensure that the conditioned air is supplied to the cabin  14 . 
   For ease of understanding, since the compressor, the condenser, the dryer, and the expansion valve are not central to the invention, they are not illustrated. However, it is considered apparent how these components interact with the present invention. 
   In addition to being bounded by the engine compartment  20  and the storage area  22 , the cabin  14  is further defined by a windshield  60  and a dashboard  62 . Located on the dashboard  62  are a temperature display  64 , an input device  66  for changing a set temperature, and the outlets  58  for dispersing conditioned air. Located in or behind the dashboard  62  is a controller  68 , which is part of the control system  10 . The control system  10  also includes an ambient temperature sensor  70 , an evaporator temperature sensor  72 , and a coolant temperature sensor  74 . 
   The ambient temperature sensor  70 , evaporator temperature sensor  72 , and coolant temperature sensor  74  are illustrated as being disposed at distinct locations in the engine compartment  20 . However, it is considered clear that other locations in the vehicle  12  also offer appropriate positions for placement of the sensors  70 ,  72 ,  74 . For example, the coolant temperature sensor  74  could be placed anywhere near where the coolant flows that would allow accurate measurement of the coolant temperature (T w ). Further, the ambient temperature sensor  70  could be disposed anywhere on the vehicle  12  that would provide satisfactory measurement of the outside air temperature (T am ). Finally, the evaporator temperature sensor  72  can be situated either on or around the evaporator  52  so as to allow adequate temperature measurement of the evaporator  52 . These sensors are illustrated as being of a contact type, however use of non-contact measurement type devices is also envisioned. 
   Operation of the vehicle  12  causes the engine  24  to gain heat from the combustion process. As the engine  24  operates, the coolant circulates through the discharge passageway  36  and absorbs heat. After leaving the engine  24 , the coolant passes through the discharge hose  42  and enters the radiator  26  and the heater core supply hose  44 . 
   For the coolant that enters the radiator  26 , the radiator fan  28  ensures that an adequate amount of air blows through the radiator  26  to sufficiently cool the coolant. Next, the coolant leaves the radiator  26  through the first supply hose  38  and enters the pump  30 . It is noted that the coolant temperature (T w ) is measured with the coolant temperature sensor  74  prior to entering the pump  30 . However, as previously disclosed, the coolant temperature (T w ) could be measured at a number of other locations. Coolant then leaves the pump  30  and enters the supply passageway  34  to again absorb heat from the engine  24 . Further, coolant is communicated from the supply passageway  34  to the discharge passageway  36  with an interconnecting passageway (not shown). 
   Additionally, coolant travels through the heater core supply hose  44  to reach the heater core  56 . After passing through the heater core  56 , the coolant is communicated through the heater core discharge hose  46  to the pump  30 . After entering the pump  30 , the coolant is discharged into the second supply hose  40 , which is connected with the supply passageway  34  of the engine  24 . 
   In order to adjust air temperature in the cabin  14 , an occupant (not shown) would change the set temperature on the temperature display  64  with the input device  66 . The set temperature is communicated to the controller  68 , as is the outside air temperature (T am ) that is sensed by the ambient temperature sensor  70 . In addition, the controller  68  receives the evaporator (T e ) and coolant (T w ) temperatures from the evaporator and coolant temperature sensors ( 72 ,  74 ), respectively. By knowing the coolant temperature (T w ), the controller  68  can estimate or predict the heater core outlet temperature (T h ). 
   Based upon the signal received from the ambient air temperature sensor  70  and the coolant temperature sensor  74 , the controller  68  either selects the predicted heater core outlet temperature (T h ) that is based upon the coolant temperature (T w ), or an alternate heater core outlet temperature (T h ′) that is based upon the outside air temperature (T am ) and the coolant temperature (T w ). After selecting either the predicted or alternate heater core outlet temperature (T h  or T h ′), the controller  68  calculates the air mix position (SW %) with the following equation: 
                   SW   ⁢           ⁢   %     =           TAO   -     T   e           T   hs     -     T   e         ×   100     +   α             (   1   )               
where:
         SW %=Air Mix Door Position   TAO=Calculated Temperature from the Outlet   T e =Evaporator Temperature   T hs =Selected Heater Core Outlet Temperature (either the predicted or alternate heater core outlet temperature (T h  or T h ′))   α=Mode Compensation Factor.       
   Based upon the calculated air mix door position (SW %), the controller  68  transmits the signal necessary for an air mix door movement device  76  to move the air mix door  48  into the appropriate orientation. As the evaporator fan  54  forces air through the heater core  56 , movement of the air mix door  48  causes more or less air to be channeled through the heater core  56 . 
   It is noted that TAO is a calculated value of outlet temperature, a term that is well known in the art and may be based upon a number of parameters, such as sensed cabin temperature, solar load, outside air temperature (T am ), etc., but is primarily based upon the desired cabin set temperature input by the occupant. It is also known in the art that the calculated outlet temperature (TAO) is commonly used in the automatic mode of operation to control fan speed and vent selection. This control setting can be modified in some portions of the control system  10  to provide for improved response, so as to help achieve a desired level of perceived comfort on the part of the occupants in the vehicle cabin  14 . Further, the mode compensation factor (α) is based upon an operating state of the HVAC system  32 . The HVAC system  32  may be operated in for example a heater, bi-level, vent, or defrost mode and each of these modes has a compensation factor (α) associated therewith. 
   The alternate heater core outlet temperature (T h ′) is preferably determined with a second lookup table located in the controller  68 . In order to determine the alternate heater core outlet temperature (T h ′), first a modified coolant temperature (T w ′), which is based upon the outside air temperature (T am ), must be ascertained. Table A shows the relationship between the outside air temperature (T am ) and the modified coolant temperature (T w ′). 
                                                                                                   TABLE A                           T am                  &gt;20   20   10   0   −10   −20   &lt;−20                            T w ′   74   74   74   71   68   68   68                        
Next, the alternate heater core outlet temperature (T h ′) is determined based upon the coolant temperature (T w ) and the modified coolant temperature (T w ′), according to Table B, as shown below.
 
                                   TABLE B                   T w     &lt;20   20 ≦ T w  &lt; T w ′   T w  ≧ T w ′   ERROR       T h ′   20   T w     T w ′   T w ′                    
As shown in Table B, depending on the coolant temperature (T w ), the corresponding alternate heater core outlet temperature (T h ′) is selected. Further, if there are difficulties in measuring the coolant temperature (T w ), the modified coolant temperature (T w ′) is used as the alternate heater core outlet temperature (T h ′).
 
   As shown in  FIG. 3 , the HVAC system  32 , the temperature display  64 , the ambient temperature sensor  70 , evaporator temperature sensor  72 , the coolant temperature sensor  74 , and the air mix door movement device  76  are electrically connected to the controller  68 . However, other means, such as for example wireless or fiber-optic communication means to connect the components  32 ,  64 ,  70 ,  72 ,  74 ,  76  with the controller  68 , are possible and contemplated. 
   A method of using the present invention is illustrated in  FIG. 4 . In Step  100 , the evaporator temperature (T e ) is measured. Then, the coolant temperature (T w ) is measured and the predicted heater core outlet temperature (T h ) is determined (Step  110 ). Preferably, the predicted heater core outlet temperature (T h ) is determined with a first lookup table that is based upon the coolant temperature (T w ). More specifically, as the coolant temperature (T w ) increases in value, the predicted heater core outlet temperature (T h ) will increase in value. The outside air temperature (T am ) is also measured (Step  120 ). In Step  130 , the controller  68  determines if the outside air temperature (T am ) is too low. If the outside air temperature (T am ) is deemed too low, an alternate heater core outlet temperature (T h ′) is substituted for the predicted heater core outlet temperature (T h ) (Step  140 ). Preferably, the alternate heater core outlet temperature (T h ′) is determined with a second lookup table, and is based upon the outside air temperature (T am ), the coolant temperature (T w ), and the modified coolant temperature (T w ′). The air mix door position (SW %) is determined based upon either the predicted heater core temperature (T h ) or the alternate heater core outlet temperature (T h ′) (Step  150 ). In Step  160 , the controller  68  controls the air mix door  48  based upon the calculated air mix door position (SW %) of Step  150 . 
   Experimentally it has been determined that many times a temperature below approximately 16° C. is considered low in most conditions. More specifically, temperatures below 11° C. are low. However, other conditions could yield a different determination of what temperatures would be considered low and this is possible and contemplated. 
   Thus, when the outside air temperature (T am ) is low, the controller  68  uses an alternate heater core outlet temperature (T h ′) in place of the predicted heater core outlet temperature (T h ) to determine the air mix door position (SW %). By using the alternate heater core outlet temperature (T h ′), which is derived from the outside air temperature (T am ) and the coolant temperature (T w ), the air mix door  48  is adjusted so an adequate amount of air passes through the heater core  56 . 
   As previously described, position of the air mix door  48  determines how much air passes through the heater core  56 . The more air that passes through the heater core  56 , the warmer the cabin  14  will become. By compensating for cold outside air temperatures (T am ) with proper adjustment of the air mix door  48 , air discharged from the outlets  58  more closely matches the TAO. Further, as discussed hereinbefore, the TAO is the calculated value of outlet temperature and primarily based upon the set temperature as input by the occupant. The present invention ensures that the inside of the cabin  14  is adequately heated and occupant comfort is maintained regardless of outside air temperature (T am ). 
   For example, prior to the present invention, it was experimentally determined that when the outside air temperature (T am ) was equal to −10° C., the predicted heater core outlet temperature (T h ) was equal to 74° C., the evaporator temperature (T e ) was equal to −8° C., the mode compensation factor (α) was equal to 5, and the TAO was equal to 55° C., the air mix door position (SW %) was calculated to be 82%. Unfortunately, when the air mix door position (SW %) was set to 82%, the temperature of the air leaving the outlet  58  was measured to be only 45° C., instead of the desired TAO of 55° C. With the present invention and the same outside air temperature (T am ), evaporator temperature (T e ), mode compensation factor (α), and TAO of the previous example, but with the alternate heater core outlet temperature (T h ′) of 68° C., the air mix door position (SW %) is set to 88%. This results in the actual temperature of the air leaving the ducts  58  being equal to the TAO. 
   As described hereinabove, the present invention solves many problems associated with previous type devices. However, it will be appreciated that various changes in the details, materials and arrangements of parts, which have been herein described and illustrated in order to explain the nature of the invention, may be made by those skilled in the art without departing from the principle and scope of the invention, as expressed in the appended claims.