Abstract:
An air conditioning system and a method of heating air flowing through a heater core of a HVAC module is disclosed. The method includes flowing essentially all of the air flowing through an evaporator through a heater core for all HVAC operating conditions. A flow control valve is opened long enough to allow a flow of hot coolant from an engine into the heater core. The valve is then closed to stop the flow of the hot coolant. When the temperature of the hot coolant is determined to have cooled to a predetermined temperature threshold, the flow control valve is then opened again to allow hot coolant to flow into the heater core.

Description:
BACKGROUND OF INVENTION 
       [0001]    The present invention relates generally to heating, ventilation and air conditioning (HVAC) systems for vehicles, and in particular to heating the air in such HVAC systems. 
         [0002]    In a conventional HVAC module, an air temperature door (blend door) is used to direct the flow of air through or around the heater core after the air flows through the evaporator, and a mixing chamber is located downstream of the heater core to allow the air to flow through the heater core to mix with the air that flows around the heater core. This allows for a uniform temperature of the air flowing from the HVAC module by mixing the cooler air that flowed around the heater core with the warmer air that flowed through the heater core. However, with these conventional systems, the HVAC module may be larger than is desired due to the space needed for the blend door and the mixing chamber, and moreover the hot coolant is being continuously pumped through the heater core, whether needed or not. 
         [0003]    Some have added a valve to stop the flow of coolant through the heater core when not needed. Others have employed a pump having pulse width modulation or on/off control in order to control the percentage of maximum coolant flow flowing through the heater core based on the current heating needs of the HVAC system. The pulsed width modulation is a linear flow control of the flowing coolant, with reduced flow when reduced capacity is needed and higher flow when higher heater capacity is needed. But these variations of the conventional system still do not overcome some of the drawbacks of the conventional HVAC module. 
       SUMMARY OF INVENTION 
       [0004]    An embodiment contemplates a method of heating air flowing through a heater core of a HVAC module. The method may comprise the steps of: flowing air through an evaporator of the HVAC module; flowing essentially all of the air flowing through the evaporator through a heater core for all HVAC operating conditions; opening a valve to cause a flow of hot coolant from an engine into the heater core long enough to replace coolant in the heater core with the hot coolant from the engine; closing the valve to stop the flow of the hot coolant into the heater core when the hot coolant has replaced the coolant in the heater core; determining a temperature of the hot coolant; and refilling the heater core with hot coolant when the temperature of the hot coolant is determined to have cooled to a predetermined temperature threshold. 
         [0005]    An embodiment contemplates an HVAC system for a vehicle. The HVAC system may comprise a HVAC module, a heater core coolant loop and a flow control valve. The HVAC module may include a blower, an evaporator downstream in an air flow stream from the blower, and a heater core located adjacent to and downstream in the air flow stream from the evaporator, the evaporator having a face area and the heater core having a face area that is essentially equal to the face area of the evaporator, and a HVAC housing containing the evaporator and the heater core and configured to always direct all of the air flow stream flowing through the evaporator through the heater core. The heater core coolant loop is configured to direct coolant from an engine to the heater core and back to the engine. The flow control valve is located in the heater core coolant loop and configured to selectively stop a flow of the coolant in the heater core coolant loop. 
         [0006]    An advantage of an embodiment is that controlling the periodic flow of coolant into the heater core allows for desired air temperature control, even if all of the air flow through the evaporator also flows through the heater core. This allows for the elimination of a blend door. The rapid flooding and stopping of flow also creates a relatively uniform temperature across the face of the heater core, thus eliminating the need for a mixing chamber downstream of the heater core. The elimination of a blend door and mixing chamber reduces the size and simplifies the packaging of the HVAC module in a vehicle. This may be particularly advantageous in small cars that have minimal room for the HVAC module. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0007]    The FIGURE is a schematic illustration of a vehicle and an HVAC system for the vehicle. 
       
    
    
     DETAILED DESCRIPTION 
       [0008]    Referring to  FIG. 1 , a vehicle, indicated generally at  10 , is shown. The vehicle  10  includes an engine compartment  12  and a passenger compartment  14 . Within the compartments  12 ,  14  are an engine cooling system  16  and a heating, ventilation and air conditioning (HVAC) system  18 . 
         [0009]    The engine cooling system  16  includes a water pump  20  that pushes water through an engine  22  and other portions of the engine cooling system  16 . This water pump  20  may be driven by the engine  22 . A radiator  24  and fan  26  are employed in a conventional fashion for removing heat from the engine coolant. A thermostat  28  is employed in a conventional fashion for selectively blocking the flow of coolant through the radiator  24  when the coolant is below a desired operating temperature. 
         [0010]    A heater core outlet  30  from the engine  22  directs coolant to an inlet  33  of an electric flow control pump  34 . The flow control pump  34  is optional, depending upon the particular vehicle in which the HVAC system  18  is employed. For example, the flow control pump  34  may be needed as a supplemental pump if the engine driven water pump  20  does not create sufficient flow to fill a heater core  38  fast enough with hot coolant (discussed below). An outlet  37  of the flow control pump  34  directs fluid to an electronically controlled flow control valve  32 . A controller  36  connects to and controls the operation of the flow control pump  34  and the flow control valve  32 . This controller  36  may be separate or may be integrated into another controller, such as an HVAC controller. The valve is an on-off (open-closed) valve that selectively allows the flow of coolant into the heater core  38 , located in a HVAC module  40 . A coolant line  42  directs coolant from the heater core  38  to an inlet to the water pump  20 , completing a heater core coolant loop  50 . The dashed lines shown in  FIG. 1  represent coolant lines through which engine coolant flows. 
         [0011]    The HVAC system  18  includes the HVAC module  40 , within which it is located a blower  44  for drawing air in through an air inlet  46  and directing it through an evaporator  48 . Downstream of the evaporator  48  is the heater core  38 . The heater core  38  has a face area essentially equal to the face area of the evaporator  48 , with the heater core  38  preferably immediately down stream of the evaporator  48 . An HVAC housing  41  is shaped to direct all of the air flowing through the evaporator  48  through the heater core  38 —without a heater core bypass flow. This arrangement can be employed since no temperature blend door is needed. Moreover, the mixing chamber downstream of the heater core  38  can be eliminated since all of the air flowing through the evaporator  48  also flows through the heater core  38 . The elimination of the room needed for a blend door and mixing chamber allows the HVAC module  40  to be smaller, thus minimizing the packaging space. The HVAC module  40  may also include a defrost outlet and door  52 , a floor outlet and door  54 , and a panel outlet and door  56 , which direct air into different portions of the passenger compartment  14 . 
         [0012]    A refrigerant portion  58  of the HVAC system  18  may include the evaporator  48 , a thermal expansion valve  60 , a refrigerant compressor  62 , and a condenser  64  connected together in a conventional fashion via refrigerant lines  66 . The compressor  62  may be driven by the engine  22  in a conventional fashion or by an electric motor, if so desired. The dash-dot lines shown in  FIG. 1  represent refrigerant lines through which refrigerant flows. 
         [0013]    Filling the refrigerant portion  58  with refrigerant and the engine cooling system  16  with coolant may be accomplished in a conventional fashion. 
         [0014]    The operation of the HVAC system  18  will now be discussed. In the HVAC module  40 , essentially all of the air flowing through the evaporator  48  also flows through the heater core  38 , so periodic flow control of the heater core  38 —that is controlling the periodic flow of hot coolant into the heater core  38 —is a main factor in controlling the HVAC module outlet air temperature. 
         [0015]    In high heat demand situations, after the coolant has been warmed-up by the engine  22 , the controller  36  will open the flow control valve  32 . The controller  36  controls the flow control valve  32  to regulate the amount of coolant flow—a greater overall flow for more heat transfer from the heater core and a lesser flow to reduce the heat transfer from the heater core. Also, the blower  44  is operated to blow air through the heater core  38 . If additional coolant flow is required to meet the high heat demand, the flow control pump  34 , if so equipped, is turned on, thus, maximizing the heat transfer into the passenger compartment  14 . 
         [0016]    At low heater loads, such as after a passenger compartment  14  has already been warmed-up or in air conditioning mode when the compressor  62  is running and cooled air flowing from the evaporator  48  needs to be warmed-up somewhat, the controller  36  will open the flow control valve  32 , quickly flooding the heater core  38  with hot coolant. Once enough flow has occurred to replace the coolant in the heater core  38  with the hot coolant, the controller  36  will stop the flow control pump  34  (if operating) and close the flow control valve  32  to stop the flow of coolant into the heater core  38 . The blower  44  is operated to blow air through the evaporator  48  and then the heater core  38 , where it absorbs heat, before being pushed out through one or more of the vents  52 ,  54 ,  56 . Upon dropping to a predetermined temperature, which may be a heater core fin temperature, a temperature measurement of coolant in the heater core  38  itself, or some other indicator of the temperature of coolant in the heater core  38  (e.g., an estimated temperature based on blower speed, ambient air temperature and time), the controller  36  will again open the valve  32  and activate the pump  34  and flood the heater core  38  with another batch of hot coolant from the engine  22 . After which, again the pump  34  will stop and the valve  32  will be closed. This process, then, is repeated to provide the heat required for the vehicle passenger compartment  14 . The blower speed or other parameters of the HVAC module  40  may be adjusted to account for the initial higher temperature of the coolant when a new batch is delivered to the heater core  38 . 
         [0017]    This rapid flooding and stopping of coolant flow may create a relatively uniform temperature across the face of the heater core  38 , with the temperature over the entire face of the heater core  38  changing relatively uniformly as the thermal energy is transferred to the air. Thus the need for any mixing chamber downstream of the heater core  38  is eliminated. 
         [0018]    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.