Abstract:
A method of operating a HVAC system in a vehicle having an engine that operates in a high efficiency mode and a less efficient mode is disclosed. The method may comprise the steps of: operating a refrigerant compressor to cool a passenger compartment and charge a cold thermal storage apparatus; determining if a cold charge in the storage apparatus has exceeded a threshold; enabling compressor cycling if the cold charge in the storage apparatus has exceeded the threshold; detecting if the engine is operating in the high efficiency mode; determining an amount of HVAC loads on the engine; determining a proximity of the engine operation to a switching point from the high efficiency mode to the less efficient mode; and conducting a HVAC load shed if the HVAC load reduction allows the engine to stay below the switching point and the compressor cycling is enabled.

Description:
BACKGROUND OF INVENTION 
       [0001]    The present invention relates generally to heating, ventilation and air conditioning (HVAC) systems for automotive vehicles, and more particularly to controlling HVAC systems having thermal storage to improve vehicle fuel economy. 
         [0002]    In order to improve the fuel economy of automotive vehicles, some are creating engine/powertrain systems to operate in high efficiency modes under certain light load operating conditions. Such high efficiency modes may include, for example, cylinder deactivation or homogeneous charge, compression ignition (HCCI) engine operating modes. Thus, it is desirable to be able to operate the vehicles for a high percentage of the time in the high efficiency modes (as opposed to less efficient normal engine operating modes). But these high efficiency modes can generally only operate when the load from the vehicle is below a certain level. 
       SUMMARY OF INVENTION 
       [0003]    An embodiment contemplates a method of operating a HVAC system in a vehicle having an engine that operates in a high efficiency mode and a less efficient mode, the method comprising the steps of: operating a refrigerant compressor to cool a passenger compartment and charge a cold thermal storage apparatus; determining if a cold charge in the cold thermal storage apparatus has exceeded a predetermined threshold; enabling compressor cycling if the cold charge in the cold thermal storage apparatus has exceeded the predetermined threshold; detecting if the engine is operating in the high efficiency mode; determining an amount of HVAC loads on the engine; determining a proximity of the engine operation to a switching point from the high efficiency mode to the less efficient mode; and conducting a HVAC load shed to reduce the HVAC loads on the engine if the HVAC load reduction allows the engine operation to stay below the switching point for the high efficiency mode and the compressor cycling is enabled. 
         [0004]    An embodiment contemplates a method of operating a HVAC system in a vehicle having an engine that operates in a high efficiency mode and a less efficient mode, the method comprising the steps of: operating a refrigerant compressor to cool a passenger compartment and charge a cold thermal storage apparatus; determining if the refrigerant compressor has been continuously operating longer than a predetermined compressor run time period; detecting if the engine is operating in the high efficiency mode; determining an amount of HVAC loads on the engine; determining a proximity of the engine operation to a switching point from the high efficiency mode to the less efficient mode; conducting a HVAC load shed to reduce the HVAC loads on the engine if the HVAC load reduction allows the engine operation to stay below the switching point for the high efficiency mode and the refrigerant compressor has been continuously operating longer than the predetermined compressor run time period; monitoring a HVAC comfort level after the HVAC load shed occurs; comparing the HVAC comfort level to a predetermined set point; and activating the refrigerant compressor when the HVAC comfort level drops below the predetermined set point. 
         [0005]    An advantage of an embodiment is that the vehicle engine/powertrain may remain in the high efficiency mode longer by using the stored thermal energy to cool a passenger cabin, thus improving the vehicle fuel economy. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0006]      FIG. 1  is a schematic view of an automotive vehicle, illustrating a first embodiment of a HVAC system. 
           [0007]      FIG. 2  is schematic view similar to  FIG. 1 , but illustrating a second embodiment. 
           [0008]      FIG. 3  is a schematic view similar to  FIG. 1 , but illustrating a third embodiment. 
           [0009]      FIG. 4  is a schematic view similar to  FIG. 1 , but illustrating a fourth embodiment. 
           [0010]      FIG. 5A and 5B  are a flow chart illustrating a method for operating the HVAC systems of  FIGS. 1-4 . 
           [0011]      FIG. 6  is a graph illustrating charging time for a cold thermal storage portion of the HVAC system. 
           [0012]      FIG. 7  is a block diagram of HVAC load shed inputs and controls. 
           [0013]      FIG. 8  is a block diagram of cold thermal storage inputs for the HVAC system. 
       
    
    
     DETAILED DESCRIPTION 
       [0014]    Referring to  FIG. 1 , a portion of an automotive vehicle, indicated generally at  10 , is shown. The vehicle  10  may have a hybrid powertrain or may be powered solely by an internal combustion engine  22 . 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 . 
         [0015]    The engine cooling system  16  includes a water pump  20  that pushes water through the 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 for removing heat from the engine coolant. A thermostat  28  may be 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. 
         [0016]    A powertrain controller  32  controls the engine operation, including switching the engine operation between a normal operating mode and a high efficiency operating mode, such as, for example, a cylinder deactivation mode where a portion of the cylinders in the engine  22  are deactivated and/or a homogeneous charge, compression ignition (HCCI) mode where a homogeneous fuel/air charge is ignited by compression. 
         [0017]    A heater core outlet  30  from the engine  22  directs coolant to a 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 . The dashed lines shown in  FIGS. 1-4  represent coolant lines through which engine coolant flows. 
         [0018]    The HVAC system  18  includes the HVAC module  40 , within which 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 , which has a blend door  50  located on its upstream side that selectively directs air around or through the heater core  38 . The HVAC module  40  may also include a defrost outlet and door  52 , a floor outlet and door  54 , and a chest height outlet and door  56 , which direct air into different portions of the passenger compartment  14 . 
         [0019]    A cooling portion  58  of the HVAC system  18  may include the evaporator  48 , a thermal expansion valve  60 , a refrigerant thermal storage bottle  61 , a refrigerant compressor  62 , and a condenser  64  connected together via refrigerant lines  66 . The dash-dot lines shown in  FIGS. 1-4  represent refrigerant lines through which refrigerant flows. The compressor  62  may be driven by the engine  22  in a conventional fashion, thus saving the cost of a separate electric motor to drive the compressor  62 , if so desired. The refrigerant thermal storage bottle  61  stores chilled refrigerant as a form of cold thermal storage. 
         [0020]    The HVAC system  18  also includes a HVAC controller  68  that communicates with the powertrain controller  32  and controls the compressor  62 , as well as the blower  44 , blend door  50  and the outlet doors  52 ,  54 ,  56 . The powertrain controller  32  may also control the fan speed  26 . Accordingly, various portions of the HVAC system  18  and engine  22  can be automatically controlled to optimize vehicle fuel economy while providing for adequate air conditioning to the passenger compartment  14 . 
         [0021]      FIG. 2  illustrates a second embodiment. Since this embodiment is similar to the first, and to avoid unnecessary repetition of the description, the same element numbers will be used for elements that are essentially the same as in the first embodiment. In this embodiment, the engine cooling system  16  and the HVAC module  40  are the same as in the first embodiment. However, the cooling portion  58  of the HVAC system  18  and thermal storage have changed. A cold thermal storage area  70  is now incorporated into the evaporator  48  rather than employing a separate thermal storage bottle in the refrigerant line between the evaporator  48  and the compressor  62 . The rest of the HVAC system  18  may be essentially unchanged. 
         [0022]      FIG. 3  illustrates a third embodiment. Since this embodiment is similar to the first, and to avoid unnecessary repetition of the description, the same element numbers will be used for elements that are essentially the same as in the first embodiment. A secondary loop  72  is now employed in the cooling portion  58  in addition to the primary refrigerant loop  74 . A refrigerant-to-liquid heat exchanger  76  is part of both loops  72 ,  74 , transferring heat from the liquid in the secondary loop  72  to the refrigerant in the primary loop  74 . The liquid may be, for example, a common engine coolant mixture of water and ethylene glycol, or it may be some other liquid with suitable heat transfer properties. A chiller  78  is now located in the HVAC module  40  instead of a refrigerant evaporator, and a pump  80  is controlled by the HVAC controller  68  to selectively pump the liquid through the secondary loop  72 . A cold thermal storage bottle  82  for storing cooled liquid is also located in the secondary loop  72 . 
         [0023]      FIG. 4  illustrates a fourth embodiment. Since this embodiment is similar to the third, and to avoid unnecessary repetition of the description, the same element numbers will be used for elements that are essentially the same as in the third embodiment. In this embodiment, the secondary loop  72  also includes a second, larger thermal storage bottle  84  and a valve  86 , controlled by the HVAC controller  68 , that can selectively direct the liquid through or around the larger thermal storage bottle  84 . This allows for increased thermal storage capacity versus the third embodiment, without increasing the cool down time of the passenger compartment  14 , but with higher costs for the additional bottle  84  and valve  86 . 
         [0024]      FIGS. 5A and 5B  are a flow chart illustrating a method for operating the HVAC systems of  FIGS. 1-4 . When operating an automotive vehicle in a high efficiency mode, the HVAC system  18  can be a significant portion of the load on the engine  22  under certain operating conditions. The following method detects if the engine  22  is near the threshold for switching to a lower efficiency mode and if there is cold thermal energy stored that can be tapped for use to continue cooling the passenger compartment  14 . If so, then the HVAC system  18  can be adjusted to reduce the load (load shed) on the engine  22 , thus allowing the engine to remain in the high efficiency mode for a longer period of time while still providing cooling to the passenger compartment  14 . 
         [0025]    When air conditioning is initially requested, the refrigerant compressor  62 , which is controlled by the HVAC controller  68 , is operated, block  200 . Also, a compressor run timer is set in the HVAC controller  68 , block  202 . The compressor  62  continues to operate until the compressor run time is greater than a predetermined run time period, block  204 . 
         [0026]    Once the compressor run time has exceeded the predetermined run time period, a cold storage charge is determined, block  206 . The cold storage may comprise, for example, any of the cold storage systems shown in FIGS.  1 - 4 —that is, a refrigerant thermal storage bottle  61  ( FIG. 1 ), a cold thermal storage area  70  in the evaporator  48  ( FIG. 2 ), a coolant thermal storage bottle  82  ( FIG. 3 ), or a larger coolant thermal storage bottle  84  and valve  86  ( FIG. 4 ). 
         [0027]      FIG. 6  illustrates an example of one way that a cold thermal storage charge is determined in block  206 , by a look-up table. For a low compressor speed (RPM) the charge capacity over a given time  304  is less than the charge capacity over that time for a medium compressor speed  304  or a high compressor speed  300 . Other empirical or mathematical methods may be used instead to determine the cold storage capacity, if so desired. 
         [0028]    Returning to  FIGS. 5A and 5B  (in view of  FIGS. 1-4 ), the refrigerant compressor  62  continues to operate, and the cold storage charge is compared to a cold storage threshold, block  208 . If the cold storage charge is not above the threshold, then the compressor  62  continues to operate and an updated cold storage charge is determined. When the cold storage charge exceeds the threshold, then compressor cycling is enabled, block  210 . That is, the compressor  62  can be turned off, when desired, and the cold thermal storage can be employed to provide the cooling to the passenger compartment  14 . 
         [0029]    If compressor cycling is enabled, it is then determined if the engine  22  is operating in high efficiency mode, block  212 . If not, then compressor operation and cold storage checks can continue. If it is operating in high efficiency mode, block  212 , then HVAC loads on the engine are determined, block  214 . 
         [0030]      FIG. 7  illustrates potential HVAC load inputs that result in additional load on the engine  22 . The electrical load from operating the blower  44 , block  400 , the increase in electrical load on the front end fan  26  due to the air conditioner operation (over and above powertrain cooling fan load), block  402 , and the electrical load needed to engage the refrigerant compressor clutch, block  404 , all contribute to the alternator load map, block  406 . The operation of the alternator (not shown) puts a load on the engine  22 , with the operation of the HVAC system  18  increasing that load. 
         [0031]    In addition, the refrigerant compressor  62  puts a load on the engine  22 . The evaporator load, block  410 , refrigerant discharge pressure, block  412 , refrigerant suction pressure, block  414 , cold storage load, block  416 , compressor speed, block  418 , and the front end fan load, block  420 , all contribute to the compressor efficiency map, block  422 , for the refrigerant compressor  62 . The alternator load map, block  406 , and the compressor efficiency map, block  422 , are combined to produce the HVAC load model, block  424 . The HVAC load model, block  424 , indicates how much load the HVAC system  18  is putting on the engine  22 . Thus, the possible power that the HVAC system  18  can shed, block  426 , is known. 
         [0032]    Returning to  FIGS. 5A and 5B  (in view of  FIGS. 1-4 ), the proximity of the engine (powertrain) operation to a transition point between high efficiency mode and a lower efficiency operating mode is determined, block  216 . Knowing the potential power that can be shed from the HVAC system  18  and the proximity of the engine operation to the transition point, a determination is made as to whether HVAC load shed reductions will allow the engine (powertrain) to remain operating below this transition point, block  218 . If not the compressor  62  continues operation, with the engine  22  switched to the less efficient operating mode, with checks at later times to determine fit he engine is again operating in the high efficiency mode. 
         [0033]    If HVAC load shed will allow the engine  22  to continue operating in the high efficiency mode, then HVAC load is shed, block  220 . The amount of power shed can be up to the amount indicated by block  426  ( FIG. 7 ). This load shed, then, may include disengaging the clutch of the compressor  62  (or reducing the compressor capacity if it is a variable compressor), reducing the speed of the blower  44 , and/or reducing the speed of the front end fan  26 —all of which will reduce the load on the engine  22 , allowing the engine  22  to remain operating in the high efficiency mode. During the HVAC load shed event, the air inlet  46  into the HVAC module  40  may be switched to increase the recirculation of air, thus reducing the cooling load on the passenger compartment  14 . The cooling of the passenger compartment  14  is achieved by using the cold thermal storage in the HVAC system  18 . Thus, a combination of HVAC controls (provided by the HVAC controller  68 ) with engine controls (provided by the powertrain controller  32 ) and cold thermal storage (provided by the thermal storage bottle  61 , cold storage area  70 , thermal storage bottle  82 , or larger thermal storage bottle  84 ) allows for improved vehicle fuel economy. 
         [0034]    Since the cooling is now being provided by the stored cold thermal energy, which is dissipated as the HVAC system  18  operates in this mode, the HVAC comfort level is monitored, block  222 . If the HVAC comfort level remains above a set point, block  224 , then the HVAC system  18  continues to use the stored cold thermal energy. If the HVAC comfort set level drops below the set point, block  224 , then the refrigerant compressor  62  is again operated. This may necessitate changing the operating mode of the engine  22  to a lower efficiency mode to account for the increased engine loads. The value of the set point may be based on maximum evaporator air discharge temperature, a breath temperature in the passenger compartment  14 , a change in breath temperature, solar load in the passenger compartment  14 , a blower speed, or a combination of some or all of these factors. 
         [0035]      FIG. 8  illustrates how the cold thermal storage inputs for the HVAC system  18  may be employed to vary the set point used in block  224 , allowing a vehicle operator to have some input into the efficiency decision relating to engine operation. That is, one may set a switch (not shown) in the passenger compartment  14  to different economy statuses, such as, for example, economy off, economy low, economy medium and economy high, block  500 . This setting determines how far the HVAC system  18  is allowed to drift from the most desired set point before activating the compressor  62  and changing the engine operating mode to a less efficient one. Certain vehicle occupants may be willing to accept greater degrees of discomfort to extend the engine efficient mode operation. Based on the switch setting, an HVAC comfort and energy controls input is set, block  502 . This may be affected by an evaporator air temperature set point, block  506  and an ambient air temperature measurement, block  504 . These values, along with a determination of engine high efficiency enablement, block  508 , a powertrain request to shed HVAC load, block  510 , and an engine run time measurement, block  512 , define cold storage inputs, block  514 , that determine how long the cold thermal storage may be employed before compressor activation is requested. 
         [0036]    Additional efficiency strategies may be employed with the method of  FIGS. 5A and 5B  to further improve the vehicle fuel economy. For example, the compressor  62  may be shut off during vehicle accelerations to improve fuel economy. The strategy may also include compressor off at engine idle and during vehicle deceleration (when sufficient cold thermal storage is available). Moreover, the compressor  62  (if variable capacity) may be operated with deeper cycling of the compressor (100% on and off) to increase efficiency, rather than modes with the compressor  62  running at a reduced capacity. 
         [0037]    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.