Abstract:
The present invention concerns a method for cooling a passenger compartment in a hybrid vehicle that operates an engine intermittently during vehicle operation, the hybrid vehicle having an HVAC system including an HVAC duct, a blower adapted to direct a flow of air through the HVAC duct, and an evaporator located within the HVAC duct. The method includes the steps of operating the blower; operating the compressor; allowing a predetermined amount of ice to form on the evaporator during operation of the compressor; turning off the vehicle engine; ceasing operation of the compressor; measuring an indicator corresponding to a remaining amount of the predetermined amount of ice formed on the evaporator; and re-starting the compressor when a predetermined air temp in air duct is reached.

Description:
RELATED APPLICATION 
     This application is a division of U.S. Ser. No. 10/853,430 filed on May 25, 2004 now U.S. Pat. No. 6,988,371. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates generally to automotive HVAC systems and methods of operating such HVAC systems. 
     Automotive HVAC systems are well known and are utilized for heating and cooling the passenger compartments of vehicles. Hybrid vehicles, which utilize a battery and an intermittently operated internal combustion engine for vehicle propulsion, have difficulty keeping the passenger compartment cool when the engine is off. When the engine is off, the HVAC compressor, typically run by a clutch connected to the engine, is also off and the temperature in the passenger compartment can rise quickly. The hybrid vehicle is most efficient when the engine is not running and, therefore, any extended increment of time that the engine is off increases fuel savings and reduces emissions. 
     It is desirable, therefore, to provide an HVAC system that allows for extended engine off time in hybrid vehicles while keeping the passenger compartment of the vehicle cool and also for pre-cooling in conventional vehicles. 
     SUMMARY OF THE INVENTION 
     The present invention concerns a method for cooling a passenger compartment in a hybrid vehicle that operates an engine intermittently during vehicle operation, the hybrid vehicle having an HVAC system including an HVAC duct, a blower adapted to direct a flow of air through the HVAC duct, and an evaporator located within the HVAC duct. The method includes the steps of operating the blower; operating the compressor, whereby refrigerant flows through the evaporator and absorbs heat from air flowing in the air duct; allowing a predetermined amount of ice to form on the evaporator during operation of the compressor; turning off the vehicle engine; performing one of ceasing or significantly reducing the capacity of the compressor; measuring an indicator corresponding to a remaining amount of the predetermined amount of ice formed on the evaporator; and performing one of re-starting or significantly increasing the capacity of the compressor when a predetermined air temperature in the air duct is reached. Alternatively, the re-starting or significantly increasing the capacity of the compressor is performed when the indicator measures an amount of ice that is less than a predetermined amount of remaining ice. 
     An advantage of the present invention is that the ice built up on the exterior surface of the evaporator is utilized when the engine is not running in hybrid vehicles to continue to provide cool air to the passenger compartment, which results in extended engine-off periods, leading to additional fuel savings and emissions reduction. 
     The method and HVAC system may also be utilized with conventional internal combustion engine vehicles whereby ice is allowed to form on the exterior surface of the evaporator, with formed ice available to provide precooling for the HVAC system at a later time. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above, as well as other advantages of the present invention, will become readily apparent to those skilled in the art from the following detailed description of a preferred embodiment when considered in the light of the accompanying drawings in which: 
         FIG. 1   a  is a schematic view of a HVAC system in accordance with the present invention; 
         FIG. 1   b  is a schematic view of an alternative embodiment of a HVAC system in accordance with the present invention 
         FIG. 2  is a block diagram of a HVAC system in accordance with the present invention; and 
         FIG. 3  is a flowchart of a method of operating the HVAC system of  FIGS. 1   a ,  1   b , and  2  in accordance with the present invention. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring now to  FIGS. 1   a  and  1   b , a HVAC system in accordance with the present invention is indicated generally at  10  in  FIG. 1   a and at  10 ′ in  FIG. 1   b . The HVAC system  10  and  10 ′ is disposed in a vehicle, indicated generally at  12 . The vehicle  12  may be a hybrid vehicle having an internal combustion engine  14  operating in conjunction with a battery (not shown) or a conventional vehicle having the internal combustion engine  14  only. The HVAC system includes a HVAC air duct  16  and a blower  18  adapted to direct a flow of air in a direction indicated by an arrow  17  through the HVAC duct  16 . An evaporator  20  is located within the HVAC duct  16  downstream of the blower  18 . A heater core  22  is located within the HVAC duct  16  downstream of the evaporator  20 . The evaporator  20  includes a refrigerant inlet  24  from and a refrigerant outlet  26  to a refrigerant circuit, indicated generally at  27 , including a refrigerant compressor  28 . Preferably, the compressor  28  is driven by the engine  14  through a clutch  30 . The compressor  28  may be a fixed displacement compressor or a variable displacement compressor, as will be appreciated by those skilled in the art. Alternatively, the compressor  28  is a variable displacement compressor that is driven by the engine but does not include a clutch, or is an electric-driven compressor. The refrigeration circuit  27 , of course, may also include a condenser (not shown), a receiver/dryer (not shown), and a thermostatic expansion valve or orifice tube (not shown) in fluid communication with the compressor  28  and the evaporator  20 . A refrigerant is contained in the refrigerant circuit  27  and so flows through the refrigerant inlet  24 , the refrigerant outlet  26 , the compressor  28 , and the evaporator  20 . The refrigerant is selectively circulated through the piping during operation of the HVAC system  10  or  10 ′, discussed in more detail below. The heater core  22  has a coolant inlet  32  from and a coolant outlet  34  to an engine cooling circuit, indicated generally at  31 , of the internal combustion engine  14 . A coolant (not shown), such as a glycol/water mixture or the like, is contained in the engine cooling circuit  31  and thus flows through the coolant inlet  32 , the coolant outlet  34 , the engine  14 , and the heater core  22 . The coolant selectively circulates through the engine cooling circuit  31  during operation of the HVAC system  10  or  10 ′, discussed in more detail below. A damper  36  is disposed in the HVAC duct  16  downstream of the evaporator  20  and adjacent the heater core  22 . The damper  36  includes an actuator (not shown) such as an electric motor or the like that is operable to selectively expose and block the heater core  22  to an air flow from the blower  18 . When the damper  36  is in a first position  36   a , the air flowing from the blower  18  in the direction  17  bypasses the heater core  22 . When the damper  36  is in a second position  36   b , the air flowing from the blower  18  in the direction  17  flows through the heater core  22 . 
     Referring now to  FIG. 1   a , a first pressure sensor  38  is disposed on an upstream surface of the evaporator  20  adjacent the blower  18  and a second pressure sensor  40  is disposed on an opposite downstream surface of the evaporator  20  adjacent the heater core  22 . The pressure sensors  38  and  40  are operable to provide signals corresponding to measured pressure values, discussed in more detail below. 
     Referring now to  FIG. 1   b , an emissivity measuring device  39 , such as a spectrometer or the like is disposed on an upstream or a downstream surface of the evaporator  20 , depending where the onset of icing is anticipated to form, such as toward the end of the last pass (not shown) of the evaporator. The emissivity measuring device  39  is operable to provide a signal that corresponds to a measured emissivity value. 
     Referring again to  FIGS. 1   a  and  1   b , a duct temperature measurement device  42 , such as a temperature sensor or the like, is disposed in the HVAC duct  16  downstream of the heater core  22 . The HVAC air duct  16  extends to a passenger compartment, indicated schematically at  44 . A passenger compartment temperature measurement device  46  is disposed in the passenger compartment  44 . A first damper  48  is disposed in the HVAC duct  16  downstream of the heater core  22  for distributing air to a floor outlet  50  in the passenger compartment  44 . A second damper  52  is disposed in the HVAC duct  16  downstream of the heater core  22  for distributing air to either or both of a torso outlet  54  or a windshield outlet  56  in the passenger compartment  44 . A recirculation damper  58  is disposed between an outside or fresh air inlet  60  and a recirculation air or return inlet  62  from the passenger compartment  44  to supply air to the blower  18 . The recirculation damper  58  can move between a first position  58   a  and a second position  58   b . The recirculation damper  58  is operable to selectively provide only fresh air from the fresh air inlet  60  (when in the first position  58   a ), only recirculated air from the return inlet  62  (when in the second position  58   b ), or a mixture of fresh air and recirculated air to the blower  18 . Each of the dampers  48 ,  52  and the recirculation damper  58  include an actuator (not shown) such as an electric motor or the like for moving the dampers  48 ,  52  and  58  between respective closed and open positions. 
     Referring now to  FIG. 2 , the HVAC system  10  or  10 ′ includes a controller  68  electrically connected to and operatively engaging the compressor  28 , such as through the clutch  30  shown in  FIG. 1 , the blower  18 , the pressure sensors  38  and  40  or emissivity measuring device  39 , the duct temperature measurement device  42 , and the passenger compartment temperature measurement device  46 . The controller  68  is electrically connected to and operatively engages the respective actuators of the dampers  48 ,  52 , and  58 . The controller  68  is preferably an electronic control unit, such as an HVAC control unit or the like. The controller  68  may be a single microprocessor or a plurality of interconnected microprocessors. Furthermore, the controller  68  may be hardware, software, or any combination thereof as will be appreciated by those skilled in the art. The controller  68  is operable to receive signals, such as from the measurement devices  38 ,  39 ,  40 ,  42 , and  46  and to transmit commands, such as to the compressor  28 , the blower  18 , and the actuators of the dampers  48 ,  52 , and  58  during operation of the HVAC system  10  or  10 ′. 
     In operation, the HVAC system  10  or  10 ′ is activated and the controller  68  activates the blower  18  to move air through the HVAC duct  16  and through the evaporator  20 . The controller  68  also sends a signal to the clutch  30  to engage and operate the compressor  28 . When the compressor  28  operates, the refrigerant is compressed in the compressor  28  and flows from the compressor  28 , to the refrigerant inlet  24 , through the tubes (not shown) or the like of the evaporator  20 , to the refrigerant outlet  26  and back to the compressor  28 . The refrigerant in the, evaporator  20  absorbs heat from air in the HVAC duct  16  flowing in the direction  17 , cooling the air for distribution to the passenger compartment  44 . As the refrigerant flows inside the evaporator  20  and begins a phase change at a given saturation temperature, the refrigerant suffers from a pressure drop due to friction with the inner surface of the tube walls. As a result of this pressure drop, at some point in the evaporator  20 , usually towards the end of last pass of the coils of the evaporator  20 , the temperature of the refrigerant drops below the freezing temperature of moisture content in air. The controller  68  allows the compressor  28  to continue to operate at this condition and the upstream surface of the evaporator  20 , therefore, is cooled such that ice is allowed to begin to form on the upstream surface of the evaporator  20 . 
     In the HVAC system  10  of  FIG. 1   a , the ice is preferably formed on the upstream surface of the evaporator  20  at a predetermined location adjacent the pressure sensor  38 . As ice continues to form on the upstream surface of the evaporator  20 , the ice accumulation will block the air flowing across the evaporator  20  on the upstream surface adjacent the pressure sensor  38 . The measured pressure at the pressure sensor  38  will be greater than the measured pressure at the pressure sensor  40  on the downstream surface of the evaporator  20 . This measured difference in pressure value (i.e., pressure drop) corresponds to an amount of ice formed on the upstream surface of the evaporator  20  and, as the ice continues to build up, the pressure drop increases. When the pressure drop reaches a value equal to a predetermined amount of ice having formed on the upstream surface of the evaporator  20 , the HVAC system  10  is again operated normally. 
     Similarly, in the HVAC system  10 ′ of  FIG. 1   b , the ice is preferably formed on the upstream surface of the evaporator  20  at a predetermined location adjacent the emissivity measuring device  39 . As ice continues to form on the upstream surface of the evaporator  20 , the ice accumulation will build up on the evaporator  20  on the upstream surface adjacent the emissivity measuring device  39 . The emissivity value measured by the emissivity measuring device  39  will change as the ice accumulated on the evaporator  20  increases. The measured emissivity value is corresponds to an amount of ice formed on the upstream surface of the evaporator  20  and, as the ice continues to build up, the emissivity value increases. The measured emissivity value is compared to a constant stored in the emissivity measuring device  39 , or a constant stored in the controller  68  or the like. When the difference between the measured emissivity value and the constant emissivity value reaches a value equal to a predetermined amount of ice having formed on the upstream surface of the evaporator  20 , a feedback signal is sent to the controller  68 , requesting a termination of the icing process. At this point, the controller sends a signal to the compressor  28  to reduce displacement, cease functioning, or the like. As a result, the temperature in the evaporator  20  would begin to rise again and the ice on the upstream surface of the evaporator  20  starts melting slowly. Once, the ice melts below a predetermined value, another signal is sent to the controller, which triggers the controller  68  to send a signal to the compressor  28  to begin functioning again, to maximize the stroke again or the like. The icing process repeats, depending on the driving schedule, ambient temperature, and other factors including but not limited to ambient humidity, the cooling load of the HVAC system  10 ′, or the like. 
     If the vehicle  12  is a hybrid vehicle, the engine  14  is selectively turned off under certain vehicle operating conditions. While the engine  14  is turned off, it can no longer drive the compressor  28 . Thus, the flow of refrigerant through the refrigerant inlet  24 , the refrigerant outlet  26 , the compressor  28 , the evaporator  20 , and the rest of the refrigeration circuit  27  is stopped. Alternatively, if the compressor  28  is an electric-driven compressor, the output of the compressor is significantly reduced or stopped in order to limit the drain on the battery. The blower  18 , however, continues to move air through the evaporator  20  and the HVAC duct  16 , and the air flowing through the evaporator  20  transfers heat to the refrigerant in the evaporator  20 . The air also transfers heat to the ice formed on the upstream surface of the evaporator  20 , gradually melting the ice. The temperature of the air flowing through the HVAC duct  16  is measured by the duct temperature measurement device  50  and monitored by the controller  68 . The pressure drop across the evaporator  20  is measured by the pressure sensors  38  and  40  and is also monitored by the controller  68 . The ice formed on the upstream surface of the evaporator  20  acts as a thermal mass in addition to the refrigerant in the evaporator  20  and allows the air in the HVAC duct  16  to continue to be cooled with the engine  14  off or the compressor  28  in a reduced output, resulting in an extended engine-off period for the hybrid vehicle, which leads to additional fuel savings and emissions reduction. After the measured duct outlet temperature is above a predetermined temperature, the engine  14  is restarted, the compressor  28  is again engaged by the clutch  30  or increased in output and the HVAC system  10  or  10 ′ functions again as discussed above. 
     Alternatively, the HVAC system  10  or  10 ′ is operated with the compressor  28  off or in reduced output until the differential measured by the pressure sensors  38  and  40  drops to or reaches a predetermined value, such as approaching zero, or until the measured emissivity value drops to or reaches a predetermined value, such as approaching the constant emissivity value stored in the emissivity measuring device  39  or in the controller  68 . After the pressure differential or the measured emissivity value reaches the respective predetermined value, the engine  14  is restarted, the compressor  28  is again engaged by the clutch  30  or increased in output and the HVAC system  10  or  10 ′ functions again as above. 
     Alternatively, even if the vehicle  12  is not a hybrid vehicle, the ice buildup on the upstream surface of the evaporator  20  can be used to lower the overall surface temperature and avoid the blast of hot air that usually occurs after shutting off the A/C system and starting it again after a short while. Then, if one turns the engine  14  off for a short period of time, for example to run an errand, and then restarts the engine  14 , the ice formed on the upstream surface of the evaporator  20  can be employed to provide pre-cooling to the passenger compartment  44  more quickly while the refrigeration circuit  27  is just beginning to operate, thus beginning the cooling process more quickly than with a conventional HVAC system. The length of the time a vehicle can be off and still provide the pre-cooling, of course, depends on the ambient temperature and solar load on the vehicle  12 . 
     Preferably, the upstream surface of the evaporator  20  where icing is desirable is shaped to prevent water from easily draining therefrom to encourage icing during operation of the HVAC system  10  or  10 ′. Furthermore, it is desirable to provide an ultraviolet (UV) light  37 , in the vicinity of drained water, such as in the HVAC duct  16  where a drain condensate tray (not shown) is located. The UV radiation from the UV light  37  kills any bacterial and/or microbial growth associated with the ice and water in the HVAC system  10  or  10 ′. 
     Referring now to  FIG. 3 , a flowchart of a method of operating the HVAC system  10  or  10 ′ in accordance with the present invention is indicated generally at  60 . In a step  62 , the engine, such as the engine  14  in  FIGS. 1   a  and  1   b , is turned off. In a step  64 , the HVAC system  10  or  10 ′ is turned to a full recirculation mode, such as by moving the damper  58  of  FIGS. 1   a  and  1   b  from the position  58   b  to the position  58   a  and a blower, such as the blower  18  in  FIG. 1 , is turned to a lower output to conserve battery power. In a step  66 , a duct outlet temperature is measured, such as by the duct temperature measurement device  42  of  FIGS. 1   a  and  1   b . In a step  68 , a passenger compartment temperature is measured, such as by the passenger compartment temperature-measurement device  46  of  FIGS. 1   a  and  1   b . In a step  70 , the duct outlet temperature is compared to the passenger compartment temperature. If the duct outlet temperature is greater than the passenger compartment temperature, a request is sent to restart the engine in a step  72 . If the duct outlet temperature is greater than the passenger compartment temperature, the HVAC system  10  or  10 ′ continues the operation of the blower to provide cooled air to a passenger compartment, such as the passenger compartment  44  in  FIGS. 1   a  and  1   b , in a step  74 . In a step  76 , the duct outlet temperature is compared to a predetermined value, such as 15 degrees Celsius. If the duct outlet temperature is greater than the predetermined temperature, a request is sent to restart the engine in a step  78 . If the evaporator outlet temperature is less than the predetermined temperature, the method  60  returns to the step  66  to measure the evaporator outlet temperature. 
     In accordance with the provisions of the patent statutes, the present invention has been described in what is considered to represent its preferred embodiment. However, it should be noted that the invention can be practiced otherwise than as specifically illustrated and described without departing from its spirit or scope.