Abstract:
A heating system for a vehicle having a power plant with a power plant coolant loop, and a method of operation, is disclosed. The heating system may include a HVAC module and a heater core coolant loop. The HVAC module includes a heater core. The heater core coolant loop includes a three-way valve having an inlet engaging the heater core for receiving a coolant, a first outlet that directs the coolant back into the heater core coolant loop, and a second outlet that directs the coolant into the power plant; a coolant pump for pumping the coolant through the heater core coolant loop; and a coolant heater located upstream of the heater core that selectively heats coolant flowing therethrough. Also, a coolant line receives the coolant from a heater core outlet of the power plant and directs the coolant into the heater core coolant loop.

Description:
BACKGROUND OF INVENTION 
     The present invention relates generally to heating, ventilation and air conditioning (HVAC) systems for vehicles. 
     The HVAC systems used in conventional vehicles are typically powered by the engine, which is continuously running, and so are not impacted by the power drain on a battery pack. Such systems are based upon the fact that a conventional (non-hybrid) vehicle&#39;s engine coolant temperature is controlled to a somewhat constant temperature, using an engine thermostat, and that the heater core coolant flow rate varies with engine speed. These HVAC systems when operating in heating modes typically adjust the position of a temperature door to achieve the desired temperature of the air flowing into a passenger compartment. 
     However, for plug-in hybrids &amp; electric vehicles, an important vehicle performance objective is vehicle range in the pure electric-vehicle mode. Such extended range electric automotive vehicles use a motor, powered by a battery, for moving the vehicle, with an engine or fuel cell used as a kind of on-board generator to recharge the battery pack. Some types of hybrid vehicles (such as plug-in hybrid vehicles) also operate for extended periods in electric only modes. In electric vehicle mode, there is no engine heat rejection and so battery pack energy is consumed in order to power the accessories. The electric only driving range of automotive vehicles, with battery powered electric motors providing the motive force, can be greatly reduced by vehicle electric accessory loads. Some of the highest electric accessory loads are used to provide heat to the passenger compartment of the vehicle for windshield defrost/defog and occupant comfort. Thus, minimizing the electric power consumption for HVAC systems can greatly improve the electric only driving range of these vehicles, as well as sometimes improve the total driving range of the vehicles. 
     Moreover, for fuel cell vehicles, the maximum fuel cell coolant temperature is limited to a lower level than with an internal combustion engine, so supplemental heat may be required to provide the desired heat to the passenger compartment for defrost and warming functions—especially when the vehicle is operating in low ambient air temperature conditions. 
     SUMMARY OF INVENTION 
     An embodiment contemplates a heating system for a vehicle having a power plant with a power plant coolant loop. The heating system may comprise a HVAC module and a heater core coolant loop. The HVAC module includes a heater core. The heater core coolant loop includes a three-way valve having an inlet engaging the heater core for receiving a coolant therefrom, a first outlet that selectively directs the coolant back into the heater core coolant loop, and a second outlet that selectively directs the coolant into the power plant; a coolant pump for pumping the coolant through the heater core coolant loop; and a coolant heater located upstream of the heater core in the heater core coolant loop that selectively heats coolant flowing therethrough. Also, a coolant line receives the coolant from a heater core outlet of the power plant and directs the coolant into the heater core coolant loop. 
     An embodiment contemplates an automotive vehicle comprising: an engine compartment having a power plant and a power plant coolant loop located therein, with the power plant coolant loop configured to direct a coolant flow out of and into the power plant, and the power plant including a heater core outlet; a passenger compartment has a HVAC module located therein, with the HVAC module including a heater core; a coolant heater configured to selectively heat a coolant just prior to the coolant entering the heater core; a coolant pump configured to selectively pump a coolant through the coolant heater and the heater core; a three-way valve having an inlet operatively engaging the heater core for receiving the coolant therefrom, a first outlet configured to selectively direct the coolant toward the coolant heater, and a second outlet configured to selectively direct the coolant into the power plant in fluid communication with the power plant coolant loop; and a coolant line for directing the coolant from the heater core outlet of the power plant toward the coolant heater. 
     An embodiment contemplates a method of operating a heating system in a vehicle, the method comprising the steps of: determining if a power plant is operating; determining if a temperature of a coolant in a power plant coolant loop is above a predetermined temperature threshold; actuating a valve to isolate a heater core coolant loop from a power plant coolant loop, activating a coolant pump in the heater core coolant loop and activating a coolant heater in the heater core coolant loop to heat the coolant in the heater core coolant loop before the coolant flows through a heater core, if the temperature in the power plant coolant loop is not above the predetermined temperature threshold; and actuating the valve to direct the coolant from the heater core coolant loop into the power plant coolant loop and the coolant from the power plant coolant loop into the heater core coolant loop if the temperature in the power plant coolant loop is at or above the predetermined temperature threshold. 
     An advantage of an embodiment is that electrical power consumption is minimized during cabin heating and defrost/defogging when the vehicle is in electric vehicle mode, during initial stages of engine-on operation (engine warm-up), and during hybrid engine operation. Supplemental heat can also be provided to fuel cell vehicles to provide the desired defrost/defog and passenger compartment warming functions. Also, electric compressor power consumption may be reduced by stopping engine coolant flow to the heater core during air conditioning operating modes. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a schematic diagram of a vehicle having a heating system according to a first embodiment. 
         FIG. 2  is a view similar to  FIG. 1 , but illustrating a different mode of operation. 
         FIG. 3  is a view similar to  FIG. 1 , but illustrating a different mode of operation. 
         FIG. 4  is a schematic diagram of a vehicle having a heating system according to a second embodiment. 
         FIG. 5  is a view similar to  FIG. 4 , but illustrating a different mode of operation. 
         FIG. 6  is a view similar to  FIG. 4 , but illustrating a different mode of operation. 
     
    
    
     DETAILED DESCRIPTION 
     Referring to  FIGS. 1-3 , a vehicle, indicated generally at  20 , is shown. The vehicle  20  may be an extended range electric vehicle. The vehicle  20  includes an engine compartment  22 , within which is mounted a power plant  24 , and a passenger compartment  26 , within which is a heating, ventilation and air conditioning (HVAC) module  28 . The power plant  24  may be, for example, an internal combustion engine or a fuel cell. The power plant  24  may have coolant lines  30  extending to a radiator  32 , which may be located adjacent to a cooling fan  34 . The coolant lines  30  and radiator  32 , along with the power plant  24 , form a power plant coolant loop  31 . Coolant lines, as disclosed herein, may be tubes, hoses or other means of directing fluid from one location to another. 
     The HVAC module  28  forms a part of a heating system  36  for the vehicle  20  (as well as part of an air conditioning system, not shown) and includes a blower  38  that draws air into the HVAC module  28  through a recirculation flow path  40  and a fresh air path  42 , with a fresh/recirculation door  44  determining the air mix from each path  40 ,  42 . An evaporator  46  extends across the module  28  downstream of the blower  38 , with a temperature door  48  just downstream from the evaporator  46 . An air temperature sensor  50  measures the temperature of the air leaving the module  28 . Between the temperature door  48  and the air temperature sensor  50  is a heater core  52 , which is part of the heating system  36 . The temperature door  48  is movable to selectively vary the percentage of the air flowing through or around the heater core  52 . One will note that, even though this heating system  36  is employed in a vehicle with a non-conventional power system, the HVAC module  28  may be the same as one employed in a conventional vehicle. This allows for re-use of existing, non-hybrid vehicle, automatic climate control HVAC module temperature door adjustment controls as well as re-use of non-hybrid vehicle HVAC modules. Thus, the cost and complexity for vehicles having conventional and optional non-conventional power train systems may be reduced. 
     The heating system  36  also includes a heater core coolant loop  54 , with a coolant line  56  extending from an outlet of the heater core  52  to an inlet to a three-way valve  58 . The three-way valve  58  also includes a first outlet  66  directing coolant to a coolant line  60  of the heater core coolant loop  54  and a second outlet  68  directing coolant to a coolant line  62  that directs coolant to a heater core inlet  59  of the power plant  24 . The heater core coolant loop  54  also includes an air separator  64 , which can receive coolant from a heater core outlet  65  of the power plant  24  or the first outlet  66  of the three-way valve  58  and direct it toward a coolant pump  70 . The coolant pump  70 , which may be electrically driven, pumps the coolant through the coolant loop  54  and directs the coolant to a coolant heater  72 . The coolant heater  72  may be a high voltage, positive temperature coefficient (PTC) or resistive heater that can provide a high rate of heat input to coolant flowing through it. A coolant inlet temperature sensor  71  may be located adjacent to the coolant heater  72  to measure the temperature of coolant entering the coolant heater  72 . The outlet of the coolant heater  72  is connected, via a coolant line  74 , to an input to the heater core  52 , thus completing the heater core coolant loop  54 . One will note that the high voltage heating components of the heating system  36  can be located outside of the passenger compartment  26 , thus avoiding the added complexity incurred when locating a high voltage component in a passenger compartment. 
     A power plant external bypass valve  76  extends between the coolant line  62  extending from the power plant heater core inlet  59  and a coolant line  78  extending from the power plant heater core outlet  65 . Also, a coolant surge tank  80  is connected to a coolant line  82  leading to an engine vent  84 , the coolant line  62 , and to a coolant line  86  leading to the air separator  64 . An internal divider wall  88  is located in the surge tank  80  and includes a small bleed hole  89 . 
     The operation of the embodiments of  FIGS. 1-3  will now be discussed. Depending upon the various operating conditions of the power plant  24  and temperature of the coolant, the heater core coolant loop  54  can be selectively isolated from or operated with the power plant coolant loop  31 . The arrowheads on the coolant lines indicate the direction of flow of the coolant for that particular mode. 
     A first heating mode of operation is illustrated in  FIG. 1  and occurs when the power plant  24  is not operating and the coolant in the power plant coolant loop  31  is not sufficiently warm to provide adequate heating to the passenger compartment  26 . In this mode, no coolant is flowing in the power plant coolant loop  31  and the three-way valve  58  is actuated to direct coolant coming from the heater core  52  through the coolant line  60  to the air separator  64 . When the coolant flows through the air separator  64 , air bubbles in the coolant flow stream are separated out into the coolant surge tank  80 . The pump  70  is activated to pump the coolant through the heater core coolant loop  54 , and the coolant heater  72  is activated to heat the coolant as the coolant flows through it. The temperature sensor  71 , measuring the temperature of the coolant entering the coolant heater  72 , allows the coolant heater  72  heat input to be adjusted to account for the temperature of the coolant entering the heater  72 . The heated coolant then flows through the heater core  52 . The temperature door  48  is actuated to direct all of the air pushed through the HVAC module  28  by the blower  38  through the heater core  52  (rather than having some air bypass the heater core). The air flowing through the heater core  52  absorbs heat from the coolant before flowing out to defrost/defog windows and warm the passenger compartment  26 . The air temperature sensor  50  may be employed to determine if air exiting the HVAC module  28  is at the desired temperature. Also, the speed of the coolant pump  70  can be controlled to optimize the coolant flow rate through the heater core  52  in order to maximize heater core efficiency. 
     A second heating mode of operation is illustrated in  FIG. 2  and occurs when the power plant  24  is operating and the coolant in the power plant coolant loop  31  is not warm enough to provide substantial heat to the heater core  52 . In this mode, the three-way valve  58 , coolant pump  70  and coolant heater  72  operate similar to the first heating mode, with the heater core coolant loop  54  isolated from the power plant coolant loop  31 . Thus, the coolant heater  72  still provides heat to the coolant before it flows into the heater core  52 . In addition, the external bypass valve  76  is opened, allowing coolant in the power plant to circulate from the heater core outlet  65  back to the heater core inlet  59 , without flowing through the heater core coolant loop  54 . 
     As the coolant warms up in the coolant loops  31 ,  54 , some coolant may flow into the coolant surge tank  80  to account for thermal expansion. The bleed hole  89  in the internal divider wall  88  prevents power plant vent bleed during power plant warm-up. And, if the three-way valve  58  has a small amount of leakage, the bleed hole  89  allows coolant to re-enter the heater core coolant loop  54 —otherwise, the pump  70  might end up pumping out all of the coolant from the heater core coolant loop  54 . The divider wall  88  with the bleed hole  89  also allows somewhat for separate levels of coolant on either side of the divider wall  88 . 
     A third heating mode of operation is illustrated in  FIG. 3  and occurs when the power plant  24  is operating and the coolant in the power plant coolant loop  31  is warm enough to provide substantial heat to the heater core  52 . In this mode, the three-way valve  58  is actuated to direct coolant from the heater core  52  to the heater core inlet  59  of the power plant  24 , and the bypass valve  76  is closed so that coolant flowing from the heater core outlet  65  of the power plant  24  flows through the coolant line  78  to the air separator  64  in the heater core coolant loop  54 . The coolant pump  70  may be activated if the coolant flow from the power plant  24  is not sufficient by itself. Also, the coolant heater  72  may be activated to provide supplemental coolant heating if the power plant  24  is not providing sufficient coolant heating by itself. Supplemental coolant heating may be needed, in particular, when the power plant  24  is a fuel cell since not as much heat rejection is available for coolant heating (as compared to an internal combustion engine power plant). 
     Even after the power plant  24  ceases operation and the vehicle is in an electric vehicle mode, while the coolant is still warm enough to provide the necessary heat to the heater core, the three-way valve  58  and bypass valve  76  may remain in their positions for the third mode of operation. This allows for additional heat to be taken from the coolant, allowing the coolant heater  72  to draw less power from the battery pack to heat the coolant. The vehicle  20  may then remain in the electric vehicle operating mode for a longer time before having to re-start the power plant  24 . 
     In addition to passenger compartment heating modes, the heating system  36  has the flexibility to stop coolant flow through the heater core  52  while the power plant  24  and the vehicle air conditioning system are operating. The bypass valve  76  is opened, the three-way valve  58  is actuated to the same position as in the first two heating modes, and the coolant pump  70  is turned off. This eliminates heater scrub, thus improving air conditioning performance. 
     Moreover, if a high power vehicle charger (not shown) is employed for recharging the battery pack (not shown) in a vehicle having an internal combustion engine for the power plant  24 , then the coolant heater  72  may be used to pre-heat the coolant. The pre-heated coolant may be directed into the power plant  24 , when started, possibly reducing emissions at start-up. 
       FIGS. 4-6  illustrate a second embodiment. Since this embodiment is similar to the first, similar element numbers will be used for similar elements, but employing 100-series numbers. The vehicle  120  still includes a heater core coolant loop  154 , a HVAC module  128 , and a power plant  124 , similar to the first embodiment. The power plant coolant loop  131 , however, is changed somewhat from the first embodiment and the bypass valve is eliminated. 
     The power plant coolant loop  131  includes a thermostat  190  that connects, via coolant line  162 , to the three-way valve  158 . The thermostat  190  interacts with a power plant water pump  192 , allowing the coolant flowing into the water pump  192  to be selectively received from the coolant lines  130  in the power plant coolant loop  131  or from the coolant line  162 . Also, a coolant temperature sensor  196  may be located at the heater core outlet  165  to measure the temperature of the coolant leaving the power plant  124 . Another coolant line  198  connects the coolant line  178  with the coolant surge tank  180 . The coolant line  130  leading to an input to the radiator  132  connects to the coolant line  178  extending from the heater core outlet  165  of the power plant  124 . 
     The three different heating modes of operation of the heating system  136  will now be discussed. The arrowheads on the coolant lines indicate the direction of flow of the coolant for that particular mode. 
     The first heating mode is illustrated in  FIG. 4  and occurs when the power plant  124  is not operating and the coolant in the power plant coolant loop  131  is not sufficiently warm to provide adequate heating to the passenger compartment  126 . In this mode, no coolant is flowing in the power plant coolant loop  131  and the three-way valve  158  is actuated to direct coolant coming from the heater core  152  through the coolant line  160  to the air separator  164  (thus isolating the heater core coolant loop  154  from the power plant coolant loop  131 ). The pump  170  is activated to pump the coolant through the heater core coolant loop  154 , and the coolant heater  172  is activated to heat the coolant as the coolant flows through it. The temperature sensor  171 , measuring the temperature of the coolant entering the coolant heater  172 , allows the coolant heater  172  heat input to be adjusted to account for the temperature of the coolant entering the heater  172 . Other factors for determining the power input to the coolant heater  172  may be the ambient air temperature and the speed of the blower  138 . The heated coolant then flows through the heater core  152 . The temperature door  148  is actuated to direct all of the air pushed through the HVAC module  128  by the blower  138  through the heater core  152  (rather than having some air bypass the heater core)—although minor temperature adjustments may be made by actuating the temperature door  148 . The air flowing through the heater core  152  will absorb heat from the coolant before flowing out to defrost/defog windows and warm the passenger compartment  126 . The air temperature sensor  150  may be employed to determine if air exiting the HVAC module  128  is at the desired temperature. Also, the speed of the coolant pump  170  can be controlled to optimize the coolant flow rate through the heater core  152  in order to maximize heater core efficiency. 
     The second heating mode is illustrated in  FIG. 5  and occurs when the power plant  124  is operating and the coolant in the power plant coolant loop  131  is not warm enough to provide substantial heat to the heater core  152 . In this mode, the three-way valve  158 , coolant pump  170  and coolant heater  172  operate similar to the first mode, with the heater core coolant loop  154  isolated from the power plant coolant loop  131 . Thus, the coolant heater  172  still provides heat to the coolant before it flows into the heater core  152 . In addition, the thermostat  190  is positioned to block coolant flow through the power plant coolant loop  131  while allowing coolant in the power plant  124  to circulate internally (indicated by the circular arrow in the power plant  124 ). 
     The third heating mode is illustrated in  FIG. 6  and occurs when the power plant  124  is operating and the coolant in the power plant coolant loop  131  is warm enough to provide substantial heat to the heater core  152 . In this mode, the three-way valve  158  is actuated to direct coolant from the heater core  152  to the heater core inlet  159  of the power plant  124 . The thermostat  190  is positioned to allow the coolant to flow through the power plant coolant loop  131  and to flow through the heater core outlet  165  of the power plant  124  to the heater core coolant loop  154 . The coolant pump  170  may be activated if the coolant flow from the power plant  124  is not sufficient by itself. Also, the coolant heater  172  may be activated to provide supplemental coolant heating if the power plant  124  is not providing sufficient coolant heating by itself—for example, at very low ambient temperatures. 
     In addition to passenger compartment heating modes, the heating system  136  has the flexibility to stop coolant flow through the heater core  152  while the power plant  124  and the vehicle air conditioning system are operating. The three-way valve  158  is actuated to the same position as in the first two heating modes, and the coolant pump  170  is turned off. This eliminates heater scrub, thus improving air conditioning performance. 
     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.