Abstract:
A method of controlling a HVAC system for a hybrid vehicle having a refrigerant compressor driven by an engine is disclosed. The method may comprise: determining a requested air conditioning operating point for a passenger compartment; estimating a time to reach the requested operating point; based on the previous steps, estimating a maximum allowed compressor off time; determining if the allowed compressor off time is greater than a minimum engine off time; if the allowed compressor off time is greater than the engine off time, determining if the vehicle is entering an allowable engine off mode; if so, commencing engine shut-off mode; if engine shut-off is anticipated, prior to commencing the shut-off mode, adjusting the HVAC system to maximize cooling of the passenger compartment with minimum energy usage; and if the engine shut-off is commenced, monitoring the HVAC system to determine when engine restart is needed to maintain comfort.

Description:
BACKGROUND OF INVENTION 
     The present invention relates generally to heating, ventilation and air conditioning (HVAC) systems for vehicles, and more particularly to HVAC systems employed with hybrid vehicles having belt driven refrigerant compressors. 
     On vehicles that employ internal combustion engines, some hybrid versions shut off the engine while stopped at a traffic light in order to improve fuel economy. For such vehicles that also employ a belt driven refrigerant compressor (i.e., the belt driven by the engine), the compressor cannot operate while the engine is off. So, while a vehicle is waiting at a stop light on a hot day, the requirement to keep passengers thermally comfortable is in direct conflict with increasing fuel economy. 
     Some have addressed this concern by using an electric driven compressor, which can operate with the engine off. However, the electric compressor operates at a higher cost in energy and materials due to the complexity and additional stages in power transfer. This higher cost may be unacceptable for certain vehicles. 
     SUMMARY OF INVENTION 
     An embodiment contemplates a method of controlling a HVAC system for a hybrid vehicle having a refrigerant compressor driven only by an engine, the method comprising the steps of: determining a requested air conditioning operating point for a passenger compartment; estimating a time to reach the requested air conditioning operating point; based on the previous two steps, estimating a maximum allowed compressor off time; determining if the maximum allowed compressor off time is greater than a minimum allowed engine off time; if the maximum allowed compressor off time is greater than the minimum allowed engine off time, determining if the vehicle is entering an allowable engine off mode; if the vehicle is in the allowable engine off mode, commencing engine shut-off mode; if engine shut-off mode is anticipated, prior to commencing the engine shut-off mode, adjusting at least one component of the HVAC system to maximize cooling of the passenger compartment with minimum energy usage; and if the engine shut-off mode is commenced, monitoring the HVAC system to determine when engine restart is needed to maintain thermal comfort in the passenger compartment. 
     An embodiment contemplates a method of controlling a HVAC system for a hybrid vehicle, the method comprising the steps of: determining an engine temperature requirement; determining an engine temperature parameter; comparing the engine temperature parameter to the engine temperature requirement; if the engine temperature parameter is greater than the engine temperature requirement, determining that a heating engine shut-off requirement is satisfied; if the heating shut-off requirement is satisfied and the vehicle is entering an allowable engine off mode, commencing an engine shut-off mode; if the heating engine shut-off requirement is satisfied, adjusting at least one component of the HVAC system to maximize heating of a passenger compartment with minimum energy usage prior to commencing the engine shut-off mode; and if the engine shut-off mode is commenced, monitoring the HVAC system to determine when engine restart is needed to maintain thermal comfort in the passenger compartment. 
     An advantage of an embodiment is that the HVAC control strategy will meet thermal comfort requirements while maximize fuel savings by reducing compressor operation of a belt driven compressor, which allows for maximum engine off time at vehicle idle in a hybrid vehicle. This is achieved while minimizing fogging, re-fogging, musty smell/humid air discharges, and excessive temperature swings in the passenger compartment. Also, maximum engine off time is achieved while providing heat to the passenger compartment. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a schematic diagram of a vehicle including a HVAC system. 
         FIGS. 2A-2B  show a flow chart illustrating a portion of a method for operating the HVAC system of  FIG. 1 . 
         FIGS. 3A-3B  show a flow chart illustrating a portion of a method for operating the HVAC system of  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION 
     Referring to  FIG. 1 , a portion of an automotive vehicle, indicated generally at  10 , is shown. The vehicle  10  may have a hybrid powertrain including 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 . 
     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. 
     A powertrain controller  32  controls the engine operation, including switching the engine operation between a normal operating mode and a deactivation (engine shut-off) mode, such as, for example, when a vehicle is stopped at a traffic light. 
     A heater core outlet  30  from the engine  22  directs coolant to a heater core  38 , located in a HVAC module  40 . Optionally, an electrically driven auxiliary coolant pump  39  may selectively pump coolant from the engine  22  to the heater core  38 . A coolant line  42  directs coolant from the heater core  38  to an inlet to the water pump  20 . The dashed lines shown in  FIG. 1  represent coolant lines through which engine coolant flows. 
     The HVAC system  18  includes the HVAC module  40 , within which is located a blower  44  for drawing in air through an air inlet  46  past a recirculation door  47  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 , depending upon the particular HVAC operating mode. 
     A cooling 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 via refrigerant lines  66 . The dash-dot lines shown in  FIG. 1  represent refrigerant lines through which refrigerant flows. The compressor  62  is driven by the engine  22 , via a belt and pulley assembly  61 . A clutch  63  may be employed to selectively connect and disconnect the compressor  62  from the driving torque of the belt and pulley assembly  61 , or, alternatively, the compressor  62  may be a variable capacity compressor. 
     The HVAC system  18  also includes a HVAC controller  68  that communicates with the powertrain controller  32  and controls the compressor  62  (or the compressor clutch as the case may be), as well as the blower  44 , blend door  50  and the outlet doors  52 ,  54 ,  56 . The powertrain controller  32  may also control the speed of the fan  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 heating and air conditioning to the passenger compartment  14 . The flow charts of  FIGS. 2A-3B  illustrate a method for operating the HVAC system  18  of  FIG. 1  to allow for adequate thermal comfort in the passenger compartment  14  while maximizing the vehicle fuel economy by maximizing the engine off time at idle. 
     The HVAC system  18  may also include various sensors for detecting a temperature or pressure at certain points in the system. For example, the HVAC system  18  may include an ambient air temperature sensor  72  for measuring ambient air temperature outside of the vehicle, a passenger compartment air temperature sensor  74  for measuring the air temperature in the passenger compartment  14 , and a solar load sensor  76  for measuring a solar load on the passenger compartment  14 . A humidity sensor  78  may be included to measure a humidity level in the passenger compartment  14 . An evaporator air temperature sensor  80  may be employed to measure the temperature of air flowing out of the evaporator  26 . Also, a coolant temperature sensor  82  may be employed to measure a temperature of coolant flowing to the heater core  38 , and another temperature sensor  84  may be employed to obtain an engine temperature, which may measure engine oil temperature. 
       FIGS. 2A-3B  are flow charts illustrating a method for operating the HVAC system  18  (in coordination with the engine operation) of  FIG. 1  to provide heat to the passenger compartment  14 . When operating a hybrid automotive vehicle, a compromise has to be made between maximizing the fuel economy and operating the HVAC system  18  to maintain thermal comfort for the passengers. 
       FIGS. 2A-2B  show a flow chart illustrating a method for managing the heating operations of the HVAC system  18  of  FIG. 1 . Ambient temperature and engine temperature are read, block  100 . The ambient temperature sensor  72  and the coolant temperature sensor  82  may be employed for determining these temperature readings. An engine temperature requirement is determined, block  102 . This engine temperature requirement is the temperature needed to allow for adequate heat to be supplied to the heater core  38  from the engine coolant. An engine oil temperature and a catalytic converter temperature are determined, block  102 . The oil temperature may be determined from the engine temperature sensor  84 , while the converter temperature may be estimated based on, for example, engine operating conditions and run time as well as the ambient temperature. The current thermal conditions of the engine  22  are the engine thermal parameters, which are indicative of the heat that can be removed from the engine  22  to provide heat to the passenger compartment  14 . The engine temperature parameters are compared to the engine temperature requirement, block  106 . If the engine temperature parameters are not greater than the engine temperature requirement, then the process starts again. If the engine temperature parameters are greater than the engine temperature requirement, then the heating engine shut-off requirement is satisfied, block  108 . 
     The heating engine shut-off requirement is just one requirement that needs to be met in order to allow engine shut-off at vehicle idle. Another condition will be discussed below relative to  FIGS. 3A and 3B . And, of course, the general vehicle and battery pack conditions need to be met that allow for engine shut-off at idle. For example, there may be a minimum engine-on time before another shut-off is allowed and the battery may require a minimum charge to allow for engine shut-off. 
     A determination is made whether passenger compartment heating is requested, block  109 . If not, the process starts again. If passenger compartment heating is requested, then a determination is made if engine shut-off is anticipated, block  110 . If not, the process starts again. If engine shut-off is anticipated, then adjustments are made to the HVAC system  18  to account for the fact that passenger compartment heating is will be provided while the engine  22  is off. This may include, activating the auxiliary coolant pump  39  to pump warm coolant from the engine  22  through the heater core  38 , adjusting the blend door to direct all air flow through the heater core  38 , adjusting the blower speed, and/or adjusting the mode door  47  to recirculate air flow, block  112 . These changes are directed to maximizing the heat available for passenger compartment heating during the periods of engine off vehicle operation. Then, engine shut-off mode is commenced, block  113 . 
     While providing heat to the passenger compartment  14  during an engine off condition, the method assures that adequate heat can continue to be supplied to the passenger compartment  14 . The HVAC sensors are read, block  114 . The HVAC sensors to be read are those that are indicative of the ability to continue providing adequate heat to the passenger compartment  14  while the engine  22  remains off. A difference between a requested heating point and a current heating point is determined, block  116 , in order to determine how far the passenger compartment temperature is from a desired temperature range. An estimated time until the engine temperature parameters are less than the engine temperature requirements is calculated, block  118 . The estimated time is compared to a time limit, block  120 . The time limit is the amount of time that the engine  22  would need to operate after restarting to provide the heat needed for the heater core  38 . Thus, the estimation is monitored and if the thermal comfort limits will be exceeded, the request for an engine restart is sent in time to allow the engine  22  to be restarted and the system returned to normal operation before the threshold is reached. 
     If the estimated time is not less than the time limit, then the process returns to block  114 . If the estimated time is less than the time limit, then the heating engine shut-off requirement is no longer satisfied, block  122 . Once this engine shut-off requirement is not satisfied, an engine restart is requested, block  124 . With the engine  22  now operating, the auxiliary pump  39  may be deactivated, and the blend door  50 , blower speed and/or the mode door  47  may be adjusted, block  126 , to pre-engine shut-off conditions. 
     Simultaneously with the method shown in  FIGS. 2A-2B , a method for controlling the air conditioning operations may be operated.  FIGS. 3A-3B  show a flow chart illustrating a method for managing the air conditioning (A/C) operations, which may include passenger compartment cooling, as well as defog/defrost operations, for the vehicle of  FIG. 1 . 
     HVAC sensors are read, block  200 . A requested A/C performance and requested A/C operating point are read, block  202 . The requested A/C performance may include maximum A/C, high fuel economy A/C performance, defogging prevention and/or defrost operation. The requested A/C operating point is the thermal comfort range requested by the vehicle occupant. A time to reaching the requested A/C point is estimated, block  204 . Also, a maximum allowed refrigerant compressor off time is estimated, block  206 . This is the time the compressor may be off while still approaching or maintaining the thermal comfort in the passenger compartment  14  within an acceptable range around the requested A/C point. The compressor off time may be zero under some operating conditions. 
     The allowed compressor off time is then compared to the minimum allowed engine off time, block  208 . The minimum allowed engine off time is the minimum amount of time for which it is advantageous to turn the engine off. If the allowed compressor off time is not greater than the minimum allowed engine off time, then the process returns to block  200 . If the allowed compressor off time is greater than the minimum allowed engine off time, then a determination is made as to whether the vehicle is in an allowable engine off mode, block  210 . That is, the general vehicle and battery pack conditions need to be met that allow for engine shut-off at idle, as well as the conditions relating to the method of  FIGS. 2A-2B . If not in allowable engine off mode, then the process returns to block  200 . If in allowable engine off mode, then the A/C engine shut-off requirement is satisfied, block  212 . If engine shut-off is not anticipated, block  214 , due to other operating conditions preventing an engine shut-off mode, then the process returns to block  200 . If engine shut-off is anticipated, then the blend door  50 , speed of the blower  44 , and/or mode door  47  are adjusted, block  216 . These adjustments may include moving the blend door  50  to divert all air flow to bypass the heater core  38 , and moving the mode door  47  to recirculate air rather than drawing in fresh air. Then, engine shut-off mode is commenced, block  217 . 
     While providing A/C (or defrost/defog) to the passenger compartment  14  during an engine off condition, the method assures that adequate A/C can continue to be supplied to the passenger compartment  14 . The HVAC sensors are read, block  218 . The HVAC sensors to be read are those that are indicative of the ability to continue providing adequate A/C to the passenger compartment  14  while the engine  22  remains off. These may include, for example, ambient temperature, relative humidity, and solar load and direction. A determination is made whether the user comfort request has changed, block  220 . A change may occur when an occupant changes the temperature or operating mode of the HVAC system  18 . Also, a comfort operating bandwidth based on the operating mode is determined, block  222 . The comfort operating bandwidth is the acceptable range of thermal comfort provided to the occupants in the passenger compartment  14 . A time to thermal comfort being outside of the comfort operating bandwidth is estimated, block  224 . 
     A comparison is then made between the estimated time and a time limit, block  226 . The time limit is an amount of time that the engine  22  would need to operate after restarting to provide the chilled refrigerant needed for the evaporator  48 . Thus, the estimation is monitored and if the comfort operating bandwidth will be exceeded, the request for an engine restart is sent in time to allow the engine  22  to be restarted and the system returned to normal operation before the threshold is reached. If the estimated time is not less than the time limit, then the process returns to block  218 . If the estimated time is less than the time limit, then the A/C engine shut-off requirement is not satisfied, block  228 . An engine restart is requested, block  230 . In addition, the blend door  50 , blower speed, recirculation door  47  and mode doors  52 ,  54 ,  56  are returned to the operating states before the engine shut-off condition. 
     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.