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 includes an HVAC system having an HVAC duct, a blower for directing a flow of air through the HVAC duct, an evaporator located within the HVAC duct, and a heater core. The heater core has a coolant inlet outlet and is located downstream of the evaporator in the HVAC duct. The method includes the steps of cooling a refrigerant; inducing a flow of the cooled refrigerant through the evaporator; blocking a flow of coolant through the coolant inlet and outlet to trap coolant in the heater core; activating the blower to move air through the evaporator and heater core; turning off the vehicle engine; measuring a duct outlet temperature; and starting the engine when the measured duct outlet temperature is above a predetermined temperature.

Description:
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 precooling 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 includes an HVAC system having an HVAC duct, a blower adapted to direct a flow of air through the HVAC duct, an evaporator located within the HVAC duct, and a heater core. The heater core has a coolant inlet and a coolant outlet and is located downstream of the evaporator in the HVAC duct. The method includes the steps of cooling a refrigerant; inducing a flow of the cooled refrigerant through the evaporator; blocking a flow of coolant through at least one of the coolant inlet and the coolant outlet to thereby trap a predetermined amount of coolant in the heater core; activating the blower to move air through the evaporator and heater core; turning off the vehicle engine; measuring a duct outlet temperature; and starting the engine when the measured duct outlet temperature is above a predetermined temperature. 
     The HVAC system in accordance with the present invention preferably includes a bypass line extending between the engine coolant inlet and the engine coolant outlet. A first valve is disposed in a one of the engine coolant outlet and the engine coolant inlet for selectively blocking flow therethrough. A second valve is disposed in another of the engine coolant inlet and the engine coolant outlet and in the bypass line for selectively diverting flow through one of the bypass line and the another of the engine coolant inlet and the engine coolant outlet. A damper is disposed in the air duct and is operable to selectively expose and block the heater core to an air flow. The HVAC system also includes a duct temperature measurement device and a controller operatively engaging the compressor, the blower, the duct temperature measurement device, the damper, the first valve, and the second valve. 
     An advantage of the present invention is that the cooled coolant in the heater core 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 the flow of coolant through the heater core may be blocked and the coolant cooled, with the trapped coolant in the heater core available to provide precooling for the HVAC system at a later time. Alternatively, the trapped coolant can be used for mild tempering or mixing to avoid excessive cooling and then reheating of the air in the HVAC duct. In the cooling mode, preventing hot coolant flowing through the heater core also advantageously reduces the temperature in the HVAC duct as a result of preventing the higher temperature heater core from warming up air flowing near it. 
    
    
     
       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 . Preferably, the blower  18  is powered by an electric motor or the like. 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  29 . 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  22 . A refrigerant (not shown) 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  22 . The refrigerant is selectively circulated through the piping during cooling operation of the HVAC system  10  and  10 , discussed in more detail below. The heater core  22  has a coolant inlet  30  from and a coolant outlet  32  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  30 , the coolant outlet  32 , 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  and  10 ′, discussed in more detail below. 
     Referring now to  FIG. 1   a,  a bypass line  34  extends between the engine coolant inlet  30  and the engine coolant outlet  32 . A first valve  36  is disposed in the engine coolant outlet  32 . A second valve  38  is disposed in the engine coolant inlet  30  and the bypass line  34 . The first valve  36  is connected to an actuator  40 , which is operable to open and close the first valve  36  for blocking flow through the engine coolant outlet  32 . The second valve  38  is a three-way valve connected to an actuator  42 , which is operable to open and close the second valve  38  for diverting flow to either of a portion  44  of the engine coolant inlet line  30  leading to the heater core  22  or the bypass line  34 , discussed in more detail below. When the valves  36  and  38  are in a first or open position, the flow of coolant is from the engine  14 , through the engine coolant inlet  30  and the valve  38 , into the heater core  22  via the portion  44 , out of the heater core  22  through a portion  46  of the engine coolant outlet line  32 , through the valve  36  and the engine coolant outlet  32  and back to the engine  14 . When the valves  36  and  38  are in a second or closed position, the flow of coolant is from the engine  14 , through the engine coolant inlet line  30 , through the valve  38 , through the bypass line  34  and back to the engine  14  through the engine coolant outlet line  32 . When the valves  36  and  38  are in the second or closed position, coolant is trapped in the heater core  22  and the portion  44  of the engine coolant inlet line  30  and the portion  46  of the engine coolant outlet line  32 . 
     Referring now to  FIG. 1   b,  the bypass line  34  extends between the engine coolant inlet  30  and the engine coolant outlet  32 . A first valve  36 ′ is disposed in the engine coolant outlet  32  and the bypass line  34 . A second valve  38 ′ is disposed in the engine coolant inlet  30  and the bypass line  34 . The first valve  36 ′ and the second valve  38 ′ are connected to an actuator  43 , which is operable to open and close both the first valve  36 ′ and the second valve  38 ′ for diverting flow to either of a portion  44 ′ of the engine coolant inlet line  30  and a portion  46 ′ of the engine coolant outlet line  32  or to the bypass line  34 , discussed in more detail below. When the valves  36 ′ and  38 ′ are in a first or open position, the flow of coolant is from the engine  14 , through the engine coolant inlet  30  and the valve  38 ′, into the heater core  22  via the portion  44 ′, out of the heater core  22  through the portion  46 ′ of the engine coolant outlet line  32 ′, through the valve  36 ′ and the engine coolant outlet  32  and back to the engine  14 . When the valves  36 ′ and  38 ′ are in a second or closed position, the flow of coolant is from the engine  14 , through the engine coolant inlet line  30 , through the valve  38 ′, through the bypass line  34 , through the valve  36 ′ and back to the engine  14  through the engine coolant outlet line  32 . When the valves  36 ′ and  38 ′ are in the second or closed position, coolant is trapped in the heater core  22  and the portion  44 ′ of the engine coolant inlet line  30  and the portion  46 ′ of the engine coolant outlet line  32 . 
     Referring again to  FIGS. 1   a  and  1   b,  a damper  48  is disposed in the HVAC duct  16  downstream of the evaporator  20  and adjacent the heater core  22 . The damper  48  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  48  is in a first position  48   a,  the air flowing from the blower  18  in the direction  17  bypasses the heater core  22 . When the damper  48  is in a second position  48   b,  the air flowing from the blower  18  in the direction  17  flows through the heater core  22 . An evaporator outlet temperature measurement device  21 , such as a temperature sensor or the like, is disposed in the HVAC duct  16  downstream of the evaporator  20 . A duct temperature measurement device  50 , such as a temperature sensor or the like, is disposed in the HVAC duct  16  downstream of the heater core  22 . A heater core temperature measurement device  51  is attached to the surface of the heater core  22 . The HVAC duct  16  extends to a passenger compartment, indicated schematically at  52 . A first damper  53   a  is disposed in the HVAC duct  16  for distributing air to a floor outlet  52   a  in the passenger compartment  52 . A second damper  53   b  is disposed in the HVAC duct  16  for distributing air to either or both of a torso outlet  52   b  or a windshield outlet  52   c  in the passenger compartment  52 . A recirculation damper  19  is disposed between an outside or fresh air inlet  55  and a return inlet  52   d  from the passenger compartment  52  to supply air to the blower  18 . The recirculation damper  19  can move between a first position  19   a  and a second position  19   b.  The recirculation damper  19  is operable to selectively provide only fresh air from the fresh air inlet  55  (when in the first position  19   a ), only recirculated air from the recirculation air inlet  52   d  (when in the second position  19   b ), or a mixture of fresh air and recirculated air to the blower  18 . Each of the dampers  53   a,    53   b  and the recirculation damper  19  preferably includes an actuator (not shown) such as an electric motor or the like for moving the particular damper  53   a,    53   b,  or  19  between respective closed and open positions. 
     Referring now to  FIG. 2 , the HVAC system  10  or  10 ′ includes a controller  54  electrically connected to and operatively engaging the compressor  28 , such as through the clutch  29  shown in  FIG. 1 , the blower  18 , the duct temperature measurement device  50 , and the actuator(s)  40 ,  42 , or  43  of the respective first valve  36  or  36 ′, and the second valve  38  or  38 ′. The controller  54  is electrically connected to and operatively engages the respective actuators of the dampers  19 ,  48 ,  53   a,  and  53   b.  The controller  54  is preferably an electronic control unit, such as an HVAC control unit or the like. The controller  54  may be a single microprocessor or a plurality of interconnected microprocessors. Furthermore, the controller  54  may be hardware, software, or any combination thereof as will be appreciated by those skilled in the art. The controller  54  is operable to receive signals, such as from the measurement devices  21 ,  50 , and  51  and to transmit commands, such as to the compressor  28 , the blower  18 , the actuator(s)  40 ,  42 , or  43 , and the actuators of the dampers  19 ,  48 ,  53   a,  and  53   b  during operation of the HVAC system  10  or  10 ′. 
     In operation, the HVAC system  10  or  10 ′ is activated and the controller  54  sends a signal for the clutch  29  to engage and operate the compressor  28 . When the compressor  28  operates, the refrigerant in the piping of the HVAC system is compressed in the compressor  28  and flows through the refrigeration circuit  27  to the refrigerant inlet  24 , through the evaporator  20 , to the refrigerant outlet  26  and back through the rest of the refrigeration circuit  27  to the compressor  28 . The controller  54  activates the blower  18  to move air through the HVAC duct  16  and through the evaporator  20 . 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 vehicle interior  52 . During startup of the HVAC system  10  or  10 ′, the valves  36  and  38  or the valves  36 ′ and  38 ′ are preferably in the first or open position and the damper  48  is in the first position  48   a.    
     At a predetermined time, such as after the passenger compartment  52  has reached a desired temperature, the controller  54  sends a signal to the actuators  40  and  42  to move the valves  36  and  38  or the controller  54  sends a signal to the actuator  43  to move the valves  36 ′ and  38 ′ from the first or open position to the second or closed position, blocking a flow of coolant through the coolant inlet  30  and the coolant outlet  32  and trapping a predetermined amount of coolant in the heater core  22  and the portions  44  and  46  or the portions  44 ′ and  46 ′ of the coolant inlet  30  and the coolant outlet  32 . Alternatively, flow is blocked in at least one of the coolant inlet  30  and the coolant outlet  32  (not shown) in order to trap a predetermined amount of coolant in the heater core  22 . The controller  54  sends a signal to the actuator of the damper  48  to move the damper  48  from at or near the first position  48   a  to at or near the second position  48   b  to direct cooled air downstream of the evaporator  20  through the heater core  22 , whereby the trapped coolant in the heater core  22  transfers heat to the air flowing in the HVAC duct  16 . The damper  48  remains in the second position  48   b  until the surface of the heater core  22  (as measured by the heater core temperature measurement device  51 ) drops to a predetermined temperature, after which the damper  48  may be moved to any position between the first position  48   a  and the second position  48   b.  Preferably, after the surface of the heater core  22  drops to the predetermined temperature, the damper  48  is moved to a position closer to the first position  48   a  in order to allow the air cooled by the evaporator  20  to flow to and cool the passenger compartment  52 . 
     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. In addition, after the engine  14  is turned off, the controller  54  sends a signal to the actuator of the damper  48  to move from the second position  48   b  to the first position  48   a  and a signal to the actuator of the damper  19  to move from the first position  19   a  to the second position  19   b.  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  continues to transfer heat to the refrigerant in the evaporator  20 . The temperature of the air flowing through the HVAC duct  16  is monitored by the duct temperature measurement device  50 . If the temperature in the HVAC duct  16  measured by the duct temperature measurement device  50  is below a predetermined amount, the damper  48  remains in the first position  48   a  and air does not flow through the heater core  22 . If the temperature in the HVAC duct  16  measured by the duct temperature measurement device  50  is above or rises to a predetermined amount, the damper  48  is moved to the second position  48   a,  allowing air to flow through the heater core  22 , with the air flowing through the heater core  22  now transferring heat to the trapped coolant in the heater core  22 . The trapped coolant in the heater core  22 , being previously cooled while the engine was running, 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. This extra cooling ability results 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  29  and the HVAC system  10  or  10 ′ functions again as described above. 
     As an alternative operating strategy, after the engine  14  is turned off and the controller has sent a signal to the damper  48  to move from the second position  48   b  to the first position  48   a  and a signal to the actuator of the damper  19  to move from the first position  19   a  to the second position  19   b,  the evaporator outlet temperature is measured by the evaporator outlet temperature measurement device  21 . If the temperature in the HVAC duct  16  at the evaporator outlet measured by the evaporator outlet temperature measurement device  21  is below a predetermined amount, the damper  48  remains in the first position  48   a  and air does not flow through the heater core  22 . If the temperature in the HVAC duct  16  at the evaporator outlet measured by the evaporator outlet temperature measurement device  21  is above or rises to a predetermined amount, the damper  48  is moved to the second position  48   a,  allowing air to flow through the heater core  22 , with the air flowing through the heater core  22  now transferring heat to the trapped coolant in the heater core  22 . The trapped coolant in the heater core  22 , being previously cooled while the engine was running, 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. This extra cooling ability results 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  29  and the HVAC system  10  or  10  functions again as described above. As another alternative operating strategy, the evaporator outlet temperature and the measured duct outlet temperature may be monitored separately by the controller  54 , as discussed above, or in conjunction to provide more robust monitoring and control of the HVAC system  10  or  10 ′. Alternatively, a temperature is monitored or measured from any location in the HVAC system  10  or  10 ′ where the measured temperature is indicative of a cooling function of the HVAC system  10  or  10 ′. 
     Alternatively, even if the vehicle  12  is not a hybrid vehicle, the flow of coolant through the heater core  22  may be blocked as outlined above and the trapped coolant in the heater core  22  can be cooled while the engine  14  is operating. 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 cooled coolant in the heater core  22  can be employed to provide pre-cooling to the passenger compartment  52  while the refrigeration circuit  27  is just beginning to operate, thus beginning the cooling process more quickly than with a conventional HVAC system. Alternatively, the trapped coolant can be used for mild tempering (mixing) to avoid excessive cooling and then reheating of the air in the HVAC duct  16 . In the cooling mode, preventing hot coolant flowing through the heater core  22  also reduces the temperature in the HVAC duct  16  as a result of preventing the higher temperature heater core  22  from warming up air flowing near it. 
     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  19  of  FIGS. 1   a  and  1   b  from the position  19   a  to the position  19   b  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 , the evaporator outlet temperature is measured, such as by the evaporator outlet temperature measurement device  21  of  FIGS. 1   a  and  1   b.  In a step  68 , the heater core surface temperature is measured, such as by the heater core temperature measurement device  51  of  FIGS. 1   a  and  1   b.  In a step  70 , the evaporator outlet temperature is compared to the heater core surface temperature. If the evaporator outlet temperature is greater than the heater core surface temperature, a damper adjacent a heater core, such as the heater core  22  and damper  48  of  FIGS. 1   a  and  1   b  is moved to a position to allow flow through the heater core in a step  72 . If the evaporator outlet temperature is less than the heater core surface temperature, the damper is moved to a position to prevent flow through the heater core in a step  74 . In a step  76  and a step  78 , the HVAC system continues the operation of the blower to provide cooled air to a passenger compartment, such as the passenger compartment  52  of  FIGS. 1   a  and  1   b.  In a step  80 , the duct outlet temperature is measured, such as by the duct temperature measurement device  50  of  FIGS. 1   a  and  1   b.  If the duct outlet temperature is greater than a predetermined temperature, such as 15 degrees Celsius, a request is sent to restart the engine in a step  82 . If the evaporator outlet temperature is less than the predetermined temperature, the method 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.