Abstract:
A powertrain thermal management system for a hybrid vehicle having provisions for passenger cabin heating and engine warm up.

Description:
FIELD OF THE INVENTION  
         [0001]    The invention relates to a thermal management system for a vehicle and more particularly to a powertrain thermal management system for a hybrid vehicle with provisions for passenger cabin heating and engine warm up.  
         BACKGROUND OF THE INVENTION  
         [0002]    A vehicle cabin heating system must be able to maintain passenger comfort at all times during operation of the vehicle, including extreme cold weather conditions. The heating system must not only be able to increase the vehicle cabin air temperature to the passenger comfort level within a reasonable amount of time of vehicle start, but also maintain the vehicle cabin temperature at the passenger comfort level.  
           [0003]    Typically, an internal combustion engine in a conventional vehicle releases sufficient heat to adequately heat the vehicle cabin at all vehicle engine loads. The conventional vehicle uses waste heat from the engine coolant for cabin heating. However, the internal combustion engine in a hybrid electric vehicle is usually smaller than the engine in a comparably sized conventional vehicle. Also, the internal combustion engine in the hybrid electric vehicle may not be operating when the vehicle is being powered by the electric motor. Moreover, while the internal combustion engine is operating, it operates at near peak efficiency and rejects less heat to the coolant. As a result, the heating system may not be able to provide sufficient heat continuously to the vehicle cabin to maintain passenger comfort. Additionally, upon cold start, the internal combustion engine in the hybrid electric vehicle typically takes longer to reach its optimum operating temperature than the internal combustion engine of the conventional vehicle.  
           [0004]    It would be desirable to produce a powertrain thermal management system for a hybrid electric vehicle which provides heat to the vehicle cabin and minimizes engine warm up time.  
         SUMMARY OF THE INVENTION  
         [0005]    Consistent and consonant with the present invention, a powertrain thermal management system for a hybrid electric vehicle which provides heat to the vehicle cabin and minimizes engine warm up time has surprisingly been discovered. The powertrain thermal management system for a hybrid vehicle comprises: a first cooling circuit having a first pump for circulating a coolant therein for removal of heat from a first heat source; a second cooling circuit having a second pump for circulating a coolant therein for removal of heat from a second heat source, the second heat source including at least one of an electric motor, a transmission heat exchanger, and an electronics water jacket or cold plate; a heater core for providing heat to a passenger cabin of the hybrid vehicle; and valve means in fluid communication with the first cooling circuit and the second cooling circuit, the valve means selectively routing coolant from at least one of the first cooling circuit and the second cooling circuit to the heater core. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0006]    The above, as well as other objects, features, and advantages of the present invention will be understood from the detailed description of the preferred embodiments of the present invention with reference to the accompanying drawings, in which:  
         [0007]    [0007]FIG. 1 is a schematic view of a powertrain thermal management system for a hybrid electric vehicle incorporating the features of the invention, wherein the hydraulic valve is positioned to cause heating of the vehicle cabin with the vehicle internal combustion engine coolant;  
         [0008]    [0008]FIG. 2 is a schematic view of the powertrain thermal management system for a hybrid electric vehicle illustrated in FIG. 1, wherein the hydraulic valve is positioned to cause heating of the vehicle cabin with the vehicle electric motor coolant;  
         [0009]    [0009]FIG. 3 is a schematic view of the powertrain thermal management system for a hybrid electric vehicle illustrated in FIG. 1, wherein the hydraulic valve is positioned to cause heating of the vehicle internal combustion engine with the vehicle electric motor coolant;  
         [0010]    [0010]FIG. 4 is a schematic view of an alternate embodiment of the powertrain thermal management system for a hybrid electric vehicle illustrated in FIGS.  1 - 3 , wherein a hydraulic valve having a single spool is used and the hydraulic valve is positioned to cause heating of the vehicle cabin with the vehicle internal combustion engine coolant;  
         [0011]    [0011]FIG. 5 is a schematic view of the powertrain thermal management system for a hybrid electric vehicle illustrated in FIG. 4, wherein the hydraulic valve is positioned to cause heating of the vehicle cabin with the vehicle electric motor coolant;  
         [0012]    [0012]FIG. 6 is a schematic view of an alternate embodiment of the powertrain thermal management system for a hybrid electric vehicle illustrated in FIGS.  1 - 3 , wherein a 2-position 4-way solenoid valve is used in place of the hydraulic valve and the valve is positioned to cause heating of the vehicle cabin with the vehicle internal combustion engine coolant;  
         [0013]    [0013]FIG. 7 is a schematic view of the powertrain thermal management system for a hybrid electric vehicle illustrated in FIG. 6, wherein the valve is positioned to cause heating of the vehicle cabin with the vehicle electric motor coolant;  
         [0014]    [0014]FIG. 8 is a schematic view of an alternate embodiment of the powertrain thermal management system for a hybrid electric vehicle illustrated in FIGS.  1 - 3 , wherein two 2-position 3-way solenoid valves are used in place of the hydraulic valve and the valves are positioned to cause heating of the vehicle cabin with the vehicle internal combustion engine coolant; and  
         [0015]    [0015]FIG. 9 is a schematic view of the powertrain thermal management system for a hybrid electric vehicle illustrated in FIG. 8, wherein the valves are positioned to cause heating of the vehicle cabin with the vehicle electric motor coolant. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0016]    Referring now to the drawings, and particularly FIG. 1, there is shown generally at  10  a powertrain thermal management system for a hybrid electric vehicle incorporating the features of the invention. The thermal management system  10  includes two cooling circuits which are used to supply heat to a heater core  12  for a passenger cabin (not shown) and an internal combustion engine  14  as needed. The first cooling circuit removes heat from coolant for the internal combustion engine  14 . The second cooling circuit removes heat from the coolant for a cold plate  16  for vehicle electronics (not shown), an electric motor water jacket  18 , and a transmission fluid heat exchanger  20 . The vehicle electronics may include for example a DC/AC inverter or a DC/DC converter. In the embodiments to be described, the coolant circuits use a coolant mixture of 50 percent ethylene glycol and 50 percent water. It is understood that other ethylene glycol and water percentages and other coolant mixtures can be used.  
         [0017]    In the first circuit, an engine coolant outlet  22  of the internal combustion engine  14  is in fluid communication with an engine radiator  24 . An engine coolant thermostat  26  is interposed between the internal combustion engine  14  and the engine radiator  24 . A primary engine radiator outlet  28  is in fluid communication with an engine water pump  30 . Either a mechanically driven or an electrically driven water pump  30  can be used. The engine water pump  30  is in fluid communication with an engine coolant inlet  32  of the internal combustion engine  14 . A secondary engine radiator outlet  34  is in fluid communication with a degas bottle  36 . The degas bottle  36  is in fluid communication with the engine water pump  30  and removes air from the coolant in the circuit. In the embodiment shown, an engine bypass conduit  38  provides fluid communication between the outlet  22  and the engine water pump  30 . The bypass conduit  38  can be removed and the thermal management system  10  will remain operable.  
         [0018]    The outlet  22  of the internal combustion engine  14  is in fluid communication with a passage  40   a  of a first spool  40  and a passage  42   b  of a second spool  42  of a hydraulic valve  44 . Any conventional hydraulic valve  44  may be used such as, for example, a solenoid or vacuum actuated linear or rotary type. The hydraulic valve  44  illustrated in FIG. 1 is a 6-way 2-position valve. Alternatively, the first spool  40  can be eliminated from the thermal management system  10  as illustrated in FIGS. 4 and 5, a 4-way 2-position hydraulic valve can be used as illustrated in FIGS. 6 and 7, or two 3-way 2-position solenoid valves can be used as illustrated in FIGS. 8 and 9. The first spool  40  and the second spool  42  are shown in the off position in FIG. 1.  
         [0019]    In the embodiment shown, the passage  42   b  of the second spool  42  is in fluid communication with a water heater  46 . The water heater  46  is in fluid communication with the heater core  12 . The water heater  46  can be eliminated if desired and the second spool  42  can be in direct fluid communication with the heater core  12 . The heater core  12  is in fluid communication with the passage  42   a  of the second spool  42  of the hydraulic valve  44 . The passage  42   a  is in fluid communication with the engine water pump In the second circuit, the cold plate  16 , the electric motor water jacket  18 , and the heat exchanger  20  are in fluid communication. As illustrated, the cold plate  16 , the electric motor water jacket  18 , and the heat exchanger  20  are connected in series. It is understood that the order of connection and arrangement of the cold plate  16 , the electric motor water jacket  18 , and the heat exchanger  20  could be changed without departing from the spirit and scope of the invention. The heat exchanger  20  is in fluid communication with a passage  40   b  of the first spool  40 . The passage  40   b  is in fluid communication with a passage  42   c  of the second spool  42 . The passage  42   c  of the second spool  42  is in fluid communication with an electric motor radiator  48 . A motor coolant thermostat  50  is interposed between and is in fluid communication with the passage  42   c  of the second spool  42  and the electric motor radiator  48 . A primary electric motor radiator outlet  52  is in fluid communication with an electric water pump  54 . The electric water pump  54  is in fluid communication with the cold plate  16 . A secondary electric motor radiator outlet  56  is in fluid communication with the degas bottle  36 . The degas bottle  36  is in fluid communication with the electric water pump  54 . In the embodiment shown, an electric motor coolant bypass conduit  58  provides fluid communication between the passage  42   c  of the second spool  42  and the electric water pump  54 .  
         [0020]    [0020]FIG. 2 illustrates the thermal management system  10  illustrated in FIG. 1 with the first spool  40  shown in the off position and the second spool  42  shown in the on position. The outlet  22  of the internal combustion engine  14  is in fluid communication with the passage  40   a  of the first spool  40  and a passage  42   e  of the second spool  42 . The passage  42   e  is in fluid communication with the engine water pump  30 , thereby bypassing the water heater  46  and the heater core  12 . The engine water pump  30  is in fluid communication with the inlet  32  of the internal combustion engine  14 . The remainder of the first circuit is unchanged from FIG. 1.  
         [0021]    The heat exchanger  20  of the second circuit is in fluid communication with the passage  40   b  of the first spool  40 . The passage  40   b  is in fluid communication with a passage  42   f  of the second spool  42 . The passage  42   f  is in fluid communication with the water heater  46  which is in fluid communication with the heater core  12 . The heater core  12  is in fluid communication with a passage  42   d  of the second spool  42 . The passage  42   d  is in fluid communication with the thermostat  50 , the electric motor radiator  48 , and the electric water pump  54  in series. The electric water pump  54  is in fluid communication with the cold plate  16 , the electric motor water jacket  18 , and the heat exchanger  20  in series. The remainder of the second circuit is unchanged from FIG. 1.  
         [0022]    [0022]FIG. 3 illustrates the thermal management system  10  illustrated in FIG. 1 with the first spool  40  shown in the on position and the second spool  42  shown in the off position. The outlet  22  of the internal combustion engine  14  is in fluid communication with a passage  40   c  of the first spool  40  and the passage  42   c  of the second spool  42 . The passage  42   c  is in fluid communication with the thermostat  50 , the electric motor radiator  48 , the electric water pump  54 , the cold plate  16 , the electric motor water jacket  18 , and the heat exchanger  20  in series. The heat exchanger  20  is in fluid communication with a passage  40   d  of the first spool  40  and the passage  42   b  of the second spool  42 . The passage  42   b  is in fluid communication with the water heater  46 , the heater core  12 , the passage  42   a,  the engine water pump  30  and the inlet  32  of the internal combustion engine  14  in series. The remainder of the thermal management system  10  is unchanged from FIG. 1.  
         [0023]    [0023]FIGS. 4 and 5 illustrate a second embodiment of the invention, a thermal management system  70  where the first spool  40  of the hydraulic valve  44  of the thermal management system  10  shown in FIGS.  1 - 3  has been eliminated. In the thermal management system  70 , an engine coolant outlet  72  of an internal combustion engine  74  is in fluid communication with an engine radiator  76  with a thermostat  78  interposed therebetween. A primary engine radiator outlet  79  is in fluid communication with an engine water pump  80  which is in fluid communication with an engine coolant inlet  82  of the internal combustion engine  74 . Either a mechanically driven or electrically driven water pump  80  can be used. A secondary engine radiator outlet  84  is in fluid communication with a degas bottle  86 . The degas bottle  86  is in fluid communication with the engine water pump  80  and removes air from the coolant in the circuit. In the embodiment shown, an engine bypass conduit  88  provides fluid communication between the outlet  72  and the engine water pump  80 . The bypass conduit  88  can be removed and the thermal management system  70  will remain operable.  
         [0024]    The outlet  72  of the internal combustion engine  74  is in fluid communication with a passage  90   b  of a spool  90  of a hydraulic valve  92 . Any conventional hydraulic valve  92  may be used such as, for example, a solenoid or vacuum actuated linear or rotary type. The spool  90  is shown in the off position in FIG. 4. In the embodiment shown, the passage  90   b  of the spool  90  is in fluid communication with a water heater  94 . The water heater  94  is in fluid communication with a heater core  96 . The water heater  94  can be eliminated and the spool  90  can be in direct fluid communication with the heater core  96 . The heater core  96  is in fluid communication with the passage  90   a  of the spool  90 . The passage  90   a  is in fluid communication with the engine water pump  80 .  
         [0025]    A cold plate  98  for vehicle electronics (not shown), an electric motor water jacket  100 , and a transmission fluid heat exchanger  102  are in fluid communication. As illustrated, the cold plate  98 , the electric motor water jacket  100 , and the heat exchanger  102  are connected in series. It is understood that the order of connection and arrangement of the cold plate  98 , the electric motor water jacket  100 , and the heat exchanger  102  could be changed without departing from the spirit and scope of the invention. The heat exchanger  102  is in fluid communication with a passage  90   c  of the spool  90 . The passage  90   c  is in fluid communication with an electric motor radiator  104  with a motor coolant thermostat  106  interposed therebetween. A primary electric motor radiator outlet  108  is in fluid communication with an electric water pump  110 . The electric water pump  110  is in fluid communication with the cold plate  98 . A secondary electric motor radiator outlet  112  is in fluid communication with the degas bottle  86 . The degas bottle  86  is in fluid communication with the electric water pump  110 . In the embodiment shown, an electric motor coolant bypass conduit  114  provides fluid communication between the passage  90   c  of the spool  90  and the electric water pump  110 .  
         [0026]    As illustrated in FIG. 5, when the spool  90  is in the on position, the outlet  72  of the internal combustion engine  74  is in fluid communication with the passage  90   e  of the spool  90 . The passage  90   e  is in fluid communication with the engine water pump  80 , thereby bypassing the water heater  94  and the heater core  96 . The engine water pump  80  is in fluid communication with the inlet  82  of the internal combustion engine  74 .  
         [0027]    The heat exchanger  102  is in fluid communication with the passage  90   f  of the spool  90 . The passage  90   f  is in fluid communication with the water heater  94  which is in fluid communication with the heater core  96 . The heater core  96  is in fluid communication with a passage  90   d  of the spool  90 . The passage  90   d  is in fluid communication with the thermostat  106 , the electric motor radiator  104 , and the electric water pump  110  in series. The electric water pump  110  is in fluid communication with the cold plate  98 , the electric motor water jacket  100 , and the heat exchanger  102  in series. The remainder of the circuit is unchanged from FIG. 4.  
         [0028]    A third embodiment of the present invention is shown in FIGS. 6 and 7. In a thermal management system  120 , an engine coolant outlet  122  of an internal combustion engine water jacket  124  is in fluid communication with an engine radiator  126  with a thermostat  128  interposed therebetween. The engine radiator  126  is in fluid communication with an engine water pump  130  which is in fluid communication with an engine coolant inlet  132  of the internal combustion engine water jacket  124 . In the embodiment shown, an engine bypass conduit  134  provides fluid communication between the outlet  122  and the engine water pump  130 . The bypass conduit  134  can be removed and the thermal management system  120  will remain operable. A check valve  136  is provided in a check valve conduit  138  between the engine water pump  130  and the outlet  122 . The check valve  136  and the check valve conduit  138  can be removed and the thermal management system  120  will remain operable.  
         [0029]    The outlet  122  of the internal combustion engine water jacket  124  is in fluid communication with a passage  140   c  of a solenoid valve  140 . The solenoid valve  140  shown is a 2-position 4-way type and is shown in the off position in FIG. 6. The passage  140   c  is in fluid communication with a heater core  142 . The heater core  142  is in fluid communication with the engine water pump  130 .  
         [0030]    A water jacket or cold plate  144  for vehicle electronics (not shown), an electric motor water jacket  146 , and a transmission fluid heat exchanger  148  are in fluid communication. As illustrated, the cold plate  144 , the electric motor water jacket  146 , and the heat exchanger  148  are connected in series. It is understood that the order of connection and arrangement of the cold plate  144 , the electric motor water jacket  146 , and the heat exchanger  148  could be changed without departing from the spirit and scope of the invention. The heat exchanger  148  is in fluid communication with a passage  140   d  of the solenoid valve  140 . The passage  140   d  is in fluid communication with an electric motor radiator  150  with a motor coolant thermostat  152  interposed therebetween. The electric motor radiator  150  is in fluid communication with an electric water pump  154 . The electric water pump  154  is in fluid communication with the cold plate  144 . An electric motor coolant bypass conduit  156  provides fluid communication between the passage  140   d  of the solenoid valve  140  and the electric water pump  154 .  
         [0031]    [0031]FIG. 7 illustrates the thermal management system  120  illustrated in FIG. 6 with the solenoid valve  140  shown in the on position. The outlet  122  of the internal combustion engine water jacket  124  is in fluid communication with a passage  140   a  of the solenoid valve  140 . The passage  140   a  is in fluid communication with the thermostat  152  which is in fluid communication with the electric motor radiator  150 . Fluid communication is provided between the electric motor radiator  150  and the electric water pump  154 . The electric water pump  154  is in fluid communication with the cold plate  144 . The cold plate  144 , the electric motor water jacket  146 , and the heat exchanger  148  are connected in series.  
         [0032]    The heat exchanger  148  is in fluid communication with a passage  140   b  of the solenoid valve  140 . Fluid communication is provided between the passage  140   b  and the heater core  142 . The heater core  142  is in fluid communication with the engine water pump  130  which is in fluid communication with the inlet  132  of the internal combustion engine water jacket  124 .  
         [0033]    A fourth embodiment of the present invention is shown in FIGS. 8 and 9. In a thermal management system  160 , an engine coolant outlet  162  of an internal combustion engine water jacket  164  is in fluid communication with an engine radiator  166  with a thermostat  168  interposed therebetween. The engine radiator  166  is in fluid communication with an engine water pump  170  which is in fluid communication with an engine coolant inlet  172  of the internal combustion engine water jacket  164 . In the embodiment shown, an engine bypass conduit  174  provides fluid communication between the engine water pump  170  and the outlet  162 . The bypass conduit  174  can be removed and the thermal management system  160  will remain operable. A check valve  176  is provided in a check valve conduit  178  between the outlet  162  and the engine water pump  170 . The check valve  176  and the check valve conduit  178  can be removed and the thermal management system  160  will remain operable.  
         [0034]    The outlet  162  of the internal combustion engine water jacket  164  is in fluid communication with a passage  180   a  of a first solenoid valve  180 . In FIG. 8, the first solenoid valve  180  shown is a 2-position 3-way type and is shown in the off position. The passage  180   a  is in fluid communication with a heater core  182 . The heater core  182  is in fluid communication with the engine water pump  170 .  
         [0035]    A water jacket or cold plate  184  for vehicle electronics (not shown), an electric motor water jacket  186 , and a transmission fluid heat exchanger  188  are in fluid communication. As illustrated, the cold plate  184 , the electric motor water jacket  186 , and the heat exchanger  188  are connected in series. It is understood that the order of connection and arrangement of the cold plate  184 , the electric motor water jacket  186 , and the heat exchanger  188  could be changed without departing from the spirit and scope of the invention. The heat exchanger  188  is in fluid communication with a passage  190   a  of a second solenoid valve  190 . In FIG. 8, the second solenoid valve  190  shown is a 2-position 3-way type and is shown in the off position. The passage  190   a  is in fluid communication with an electric motor radiator  192  with a motor coolant thermostat  194  interposed therebetween. The electric motor radiator  192  is in fluid communication with an electric water pump  196 . The electric water pump  196  is in fluid communication with the cold plate  184 . An electric motor coolant bypass conduit  198  provides fluid communication between the passage  190   a  of the second solenoid valve  190  and the electric water pump  196 .  
         [0036]    As illustrated in FIG. 9, when the first solenoid valve  180  and the second solenoid valve  190  are in the on position, the outlet  162  of the internal combustion engine water jacket  164  is in fluid communication with a passage  180   b  of the first solenoid valve  180 . The passage  180   b  is in fluid communication with the thermostat  194 , the motor radiator  192 , the motor water pump  196 , the cold plate  184 , the electric motor water jacket  186 , and the transmission fluid heat exchanger  188  in series. The transmission heat exchanger  188  is in fluid communication with a passage  190   b  of the second solenoid valve  190 . The passage  190   b  is in fluid communication with the heater core  182 . The heater core  182  is in fluid communication with the engine water pump  170 . The remainder of the circuit is unchanged from FIG. 8.  
         [0037]    The operation of the embodiments of the invention will now be described. The internal combustion engine cooling circuit of FIGS.  1 - 3  facilitates maintaining the internal combustion engine  14  at its optimum operating temperature. The coolant, circulated by the water pump  30 , removes the waste heat from the engine  14  and carries the waste heat to the engine radiator  24  where the excess heat is rejected to the ambient air. The thermostat  26  controls the coolant flow through the engine radiator  24  and the bypass conduit  38 . The coolant flowing out of the engine coolant outlet  22  returns to the engine water pump  30  through one or more of three possible flow paths, illustrated in FIGS.  1 - 3 . The coolant can return to the engine water pump  30  through the bypass conduit  38 , the hydraulic valve  44 , or the engine radiator  24 .  
         [0038]    During warm up of the internal combustion engine  14 , the thermostat  26  is closed and the coolant flows only through the bypass conduit  38  and the hydraulic valve  44 . Depending on the position of the first spool  40  and the second spool  42 , the engine coolant entering the hydraulic valve  44  returns to the engine water pump  30  either after flowing through the heater core  12  (illustrated in FIG. 1) or bypassing the heater core  12  (illustrated in FIG. 2).  
         [0039]    The electric motor cooling circuit helps maintain the vehicle electronics, the electric motor  18 , and the transmission at their optimum operating temperatures. The coolant, circulated by an electric water pump  54 , carries the waste heat from the vehicle electronics, the electric motor  18 , and the transmission to the electric motor radiator  48  where the excess heat is rejected to the ambient air. The transmission heat exchanger  20  is a liquid to liquid type which transfers the heat from the transmission fluid to the motor coolant.  
         [0040]    Depending upon the positions of the first spool  40  and the second spool  42 , the motor coolant entering the hydraulic valve  44  can take three possible flow routes. The coolant either bypasses the heater core  12  (illustrated in FIG. 1), flows through the heater core  12  and through the remainder of the electric motor cooling circuit (illustrated in FIG. 2), or flows through the heater core  12  and the internal combustion engine cooling circuit before returning to the electric motor cooling circuit (illustrated in FIG. 3). The thermostat  50  and the bypass conduit  58  facilitate control of the coolant flow through the electric motor radiator  48 .  
         [0041]    The hydraulic valve  44  helps provide heat to a vehicle cabin (not shown) either from the engine cooling circuit (illustrated in FIG. 1) or from the motor cooling circuit (illustrated in FIG. 2). The following table lists the coolant flow paths in the thermal management system  10  for the different spool positions.  
                                                       First   Second               Spool   Spool   Cooling Circuit Characteristics                           Off   Off   Heater Core is connected to engine                   cooling circuit.                   Motor coolant bypasses the heater                   core.           On   Off   Heater Core is connected to motor                   cooling circuit.                   Engine coolant bypasses the heater                   core.           Off   On   Both circuits are connected through                   the hydraulic valve.                   Motor coolant is used to warm up the                   engine.           On   On   Both circuits are connected through                   the hydraulic valve.                   Motor coolant is used to warm up the                   engine.                      
 
         [0042]    A vehicle thermal control module (not shown) sends a signal for actuation of the hydraulic valve  44 . Two sensors (not shown), one in the engine cooling circuit and the other in the motor cooling circuit read the respective coolant temperatures and a signal is transmitted to the control module. When the coolant in the engine cooling circuit is hotter than the coolant in the motor cooling circuit, the hydraulic valve  44  is actuated to connect the heater core  12  to the engine cooling circuit (illustrated in FIG. 1). The hot engine coolant thus provides heat to the heater core  12  and the coolant from the motor cooling circuit bypasses the heater core  12 .  
         [0043]    When the coolant in the motor coolant circuit is hotter than the coolant in the engine coolant circuit, the hydraulic valve  44  is actuated to connect the heater core  12  to the motor cooling circuit (illustrated in FIG. 2). The hot motor coolant thus provides heat to the heater core  12  and the coolant from the engine cooling circuit bypasses the heater core  12 .  
         [0044]    When the internal combustion engine  14  is cold and the coolant in the motor cooling circuit is hot, the hydraulic valve  44  is actuated to connect the motor cooling circuit to the engine cooling circuit (illustrated in FIG. 3). Thus, the waste heat from the motor cooling circuit is used to warm up the internal combustion engine  14 . If the internal combustion engine  14  warm up configuration is not desired, only a single spool is required in the hydraulic valve as illustrated in FIGS. 4 and 5.  
         [0045]    In the embodiment illustrated in FIGS. 6 and 7, a 4-way 2-position solenoid valve  140 , as opposed to a 6-way, 2-position valve is used to control the flow between the engine cooling circuit and the motor cooling circuit. When the solenoid valve  140  is in the off position as shown in FIG. 6, the engine cooling circuit and motor cooling circuit are maintained as independent circuits. The motor water pump  154  pumps the motor coolant through the cold plate  144 , the electric motor water jacket  146 , the heat exchanger  148 , the solenoid valve  140 , and either the bypass conduit  156  or the thermostat  152  and the motor radiator  150  and back to the motor water pump  154 . The engine water pump  130  pumps the engine coolant through the engine water jacket  124  and back to the engine water pump  130  through a parallel combination of the bypass conduit  134 , the heater core  142 , and the thermostat  128  and engine radiator  126 .  
         [0046]    When the coolant is cold in the engine cooling circuit and there is a need for engine and/or passenger cabin warm up, the solenoid valve  140  can be switched to the on position resulting in a crossover connection as illustrated in FIG. 7. The warm coolant from the cold plate  144 , electric motor water jacket  146 , and heat exchanger  148  flows through the solenoid valve  140 ; the heater core  142 ; a parallel combination of the check valve  136 , the bypass conduit  134 , and the engine water jacket  124 ; the solenoid valve  140 ; a parallel combination of the bypass conduit  156  and the thermostat  152  and the motor radiator  150 . The coolant does not pass through the engine radiator  126  because it is restricted by the thermostat  128  due to the low engine coolant temperature.  
         [0047]    The first solenoid valve  180  and the second solenoid valve  190  shown in FIGS. 8 and 9 can replace the solenoid valve  140  shown in FIGS. 6 and 7 to achieve an equivalent thermal management system  160 .  
         [0048]    From the foregoing description, one ordinarily skilled in the art can easily ascertain the essential characteristics of this invention and, without departing from the spirit and scope thereof, can make various changes and modifications to the invention to adapt it to various usages and conditions.