Patent Publication Number: US-8978596-B2

Title: Powertrain cooling system with cooling flow modes

Description:
TECHNICAL FIELD 
     The present teachings generally include a powertrain cooling system and a method for cooling a powertrain. 
     BACKGROUND 
     Rapid warm-up of engine coolant, engine oil and transmission oil after a cold start can improve vehicle fuel economy. A cold start is a start-up of the vehicle when the vehicle has not been running and the engine and transmission are relatively cold. Engine warm-up is especially challenging for diesel and hybrid applications, as less fuel is burned. 
     SUMMARY 
     A powertrain cooling system is configured to allow rapid warm-up of powertrain components and fluids, improving fuel economy by reducing frictional losses. The powertrain cooling system includes a coolant pump and a plurality of coolant flow passages. A first three-position valve is operatively connected with an outlet of the coolant pump and has a first, a second, and a third position to at least partially establish different coolant flow modes through the coolant flow passages. Coolant flow from the coolant pump is blocked from both the cylinder head and the engine block in a first of the coolant flow modes when the three-position valve is in the first position. Coolant flow from the coolant pump is provided to the cylinder head and is blocked from the engine block in a second of the coolant flow modes when the three-position valve is in the second position. Coolant flows from the coolant pump to the engine block and from the engine block to the cylinder head in a third of the coolant flow modes when the three-position valve is in the third position. 
     Accordingly, warming of the cylinder head and the engine block can be separately controlled. For example, a controller can be operatively connected to the first three-position valve and to temperature sensors. A first temperature sensor can be positioned in thermal communication with the cylinder head and with the controller to indicate a cylinder head temperature. A second temperature sensor can be positioned in thermal communication with the engine block and operatively connected to the controller to indicate an engine block temperature. The controller can be configured to (i) place the first three-position valve in the first position when the first temperature sensor indicates the cylinder head temperature is less than a first predetermined temperature, (ii) place the first three-position valve in the second position when the first temperature sensor indicates that the cylinder head temperature is greater than the first predetermined temperature and the engine block temperature is less than a second predetermined temperature; and (iii) place the first three-position valve in the third position when the first temperature sensor indicates that the engine block temperature is greater than the second predetermined temperature. The cylinder head can thus be cooled prior to cooling of the engine block. 
     Heating and cooling of the transmission and engine oils can also be controlled by the control system with the use of heat exchangers and a second three-position valve. An engine heat exchanger can be positioned in thermal communication with engine oil in the engine block. A transmission heat exchanger can be placed in thermal communication with transmission oil in the transmission. A second three-position valve can be positioned in the coolant flow passages downstream of the engine block in the coolant flow, operatively connected with the controller. Coolant flow is provided to the engine heat exchanger and is blocked from the transmission heat exchanger when the second three-position valve is in a first position. Coolant flow is provided to the transmission heat exchanger and is blocked from the engine heat exchanger when the second three-position valve is in a second position. Coolant flow is provided to both of the engine heat exchanger and the transmission heat exchanger when the second three-position valve is in the third position. 
     Optionally, an exhaust heat recovery device heat exchanger (EHRDHE) can be positioned at least partially within the exhaust system and in thermal communication with the coolant flow in the coolant flow passages upstream of the second three-position valve. A bypass valve that has a heat exchange position and a bypass position is operable to direct exhaust flow through the EHRDHE in the heat exchange position and to bypass the EHRDHE in the bypass position. The bypass valve is controlled to be in the heat exchange position when the second three-position valve is in the first position and when the second three-position valve is in the second position, and is controlled to be in the bypass position when the second three-position valve is in the third position. 
     The powertrain cooling system may also include a radiator operatively connected to the coolant flow passages. A radiator valve may be positioned in the coolant flow passages between the radiator and an inlet of the water pump. The radiator valve is configured to have an open position than permits coolant flow through the radiator and a closed position that prevents coolant flow through the radiator. The radiator valve may be operatively connected to the controller and controlled to be in the closed position in the first and the second of the coolant flow modes. The radiator valve can be controlled to be in the open position in the third coolant flow mode when the second three-position valve is in the third position and the coolant temperature is indicative of the engine oil temperature and the transmission oil temperature being greater than a predetermined maximum oil temperature. The predetermined maximum oil temperature is greater than the predetermined oil temperature. 
     The powertrain cooling system can also be controlled to assist with heating of the vehicle passenger compartment. Specifically, a passenger compartment heater can be positioned in thermal communication with the coolant flow in the coolant flow passages downstream of the cylinder head and upstream of the second three-position valve. Heat from the coolant is thus used to heat the passenger compartment via the passenger compartment heat exchanger. 
     A method of cooling a powertrain that has an engine with a cylinder head and an engine block includes controlling a first three-position valve to a first position to block coolant flow to the engine when a temperature of the cylinder head is less than a first predetermined temperature. The first three-position valve is positioned upstream of the engine and downstream of a coolant flow pump. The method further includes controlling the first three-position valve to a second position to direct the coolant flow to the cylinder head and block coolant flow from the engine when the temperature of the cylinder head is greater than the first predetermined temperature and a temperature of the engine block is less than a second predetermined temperature. Under the method, the first three-position valve is controlled to a third position to direct the coolant flow to both the cylinder head and the engine block when the temperature of the engine block is greater than the second predetermined temperature. 
     The above features and advantages and other features and advantages of the present teachings are readily apparent from the following detailed description of the best modes for carrying out the present teachings when taken in connection with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic illustration of a powertrain cooling system and a portion of a powertrain, with the cooling system in a first coolant flow mode that has no coolant flow. 
         FIG. 2  is a schematic illustration of the powertrain cooling system and powertrain of  FIG. 1 , with the powertrain cooling system in a second coolant flow mode with coolant flow to a cylinder head of the engine and to an engine heat exchanger, with an exhaust heat recovery device heat exchanger in a heat exchange mode, and with no coolant flow through a radiator. 
         FIG. 3  is a schematic illustration of the powertrain cooling system and powertrain of  FIG. 1 , with the powertrain cooling system in a third coolant flow mode with coolant flow to both an engine block and the cylinder head of the engine and to a transmission heat exchanger, with the exhaust heat recovery device heat exchanger in a heat exchange mode, and with no coolant flow through a radiator. 
         FIG. 4  is a schematic illustration of the powertrain cooling system and powertrain of  FIG. 1 , with the powertrain cooling system in a fourth coolant flow mode with coolant flow to both an engine block and the cylinder head of the engine, to both the engine heat exchanger and the transmission heat exchanger, with the exhaust heat recovery device heat exchanger in a heat exchange mode, and with no coolant flow through a radiator. 
         FIG. 5  is a schematic illustration of the powertrain cooling system and powertrain of  FIG. 1 , with the powertrain cooling system in a fifth coolant flow mode with coolant flow to both an engine block and the cylinder head of the engine, to both the engine heat exchanger and the transmission heat exchanger, with the exhaust heat recovery device heat exchanger in a bypass mode and with coolant flow through a radiator. 
         FIG. 6  is a schematic illustration in cross-sectional view of the first three-position valve of  FIG. 1  in a first position. 
         FIG. 7  is a schematic illustration in cross-sectional view of the first three-position valve of  FIG. 1  in a second position. 
         FIG. 8  is a schematic illustration in cross-sectional view of the first three-position valve of  FIG. 1  in a third position. 
         FIG. 9  is a schematic illustration in cross-sectional view of the second three-position valve of  FIG. 1  in a first position. 
         FIG. 10  is a schematic illustration in cross-sectional view of the second three-position valve of  FIG. 1  in a second position. 
         FIG. 11  is a schematic illustration in cross-sectional view of the second three-position valve of  FIG. 1  in a third position. 
     
    
    
     DETAILED DESCRIPTION 
     Referring to the drawings, wherein like reference numbers refer to like components throughout the several views,  FIG. 1  shows a vehicle  10  that has a powertrain  12  and a powertrain cooling system  14  operable in multiple coolant flow modes to increase vehicle efficiency as described herein. The powertrain  12  includes an engine  16  that has an engine block  18  and a cylinder head  20 . The powertrain  12  also includes a transmission  22  that is operatively connected to the engine  16  and driven by the engine  16  to propel the vehicle  10 . Additionally, the vehicle  10  includes a passenger compartment heater  23  operable to provide heat to a passenger compartment that is in thermal communication with the heater  23 . The passenger compartment is not shown, but is well understood in the art as a volume surrounded by the vehicle body in which passengers sit in the vehicle  10 . The passenger compartment is adjacent the heater  23 , which may be underneath the hood of the vehicle  10  in an engine compartment, so that when air is blown across the heater  23  into the passenger compartment, the air is heated by the heater  23 . 
     The engine  16  has an exhaust system  24  that includes an exhaust manifold  26  mounted to the cylinder head  20 . Exhaust gas is discharged from the engine  16  through the exhaust manifold  26  and an exhaust pipe  28  operatively connected thereto. An exhaust heat recovery device heat exchanger (EHRDHE)  30  is positioned in thermal communication with coolant flow in the cooling system  14  and is selectively in thermal communication with the exhaust gas in the exhaust pipe  28  as explained herein. A bypass valve  32  is controllable between two different positions. In a heat exchange position, exhaust gas flows through the EHRDHE  30 . When the bypass valve  32  is in a second, bypass position, the exhaust gas flows through a bypass conduit  34  connected to the exhaust pipe  28  to bypass the EHRDHE  30 . 
     The powertrain cooling system  14  is provided to regulate the flow of coolant and to regulate exhaust flow in order to provide warm-up of the components and fluids of the powertrain  12  in the priority most beneficial for fuel efficiency, and then maintain optimal temperatures. The powertrain cooling system  14  includes multiple coolant flow passages  50 A,  50 B,  50 C,  50 D,  50 E,  50 F,  50 G,  50 H,  50 J,  50 K,  50 P,  50 Q,  50 R, and  50 S through which coolant can be pumped by a pump  52 , referred to herein as a water pump or a coolant pump. The coolant flow passages  50 A,  50 B,  50 C,  50 D,  50 E,  50 F,  50 G,  50 H,  50 J,  50 K,  50 P,  50 Q,  50 R, and  50 S may be conduits or flexible or rigid tubing, or may be bored, drilled, cast or otherwise formed passages in any vehicle component. The pump  52  has an inlet  52 A and an outlet  52 B. The pump  52  may be driven by the engine  16 . Coolant flow through the passages  50 A,  50 B,  50 C,  50 D,  50 E,  50 F,  50 G,  50 H,  50 J,  50 K,  50 P,  50 Q,  50 R, and  50 S is controlled by multiple valves  54 ,  56 ,  58  under the control of a controller  60  to establish different cooling flow modes. The position of the bypass valve  32  is also controlled by the controller  60 . 
     The valve  54  is referred to as a first three-position valve. The valve  54  has an inlet  54 A connected to the outlet  52 B of the pump  52  by the passage  50 A, a first outlet  54 B connected to the cylinder head  20  by the passage  50 B, and a second outlet  54 C connected to the engine block  18  by the passage  50 C. The valve  54  is downstream of the pump  52  and upstream of the engine  16  in the direction of coolant flow through the passages  50 A,  50 B,  50 C. The direction of coolant flow, when coolant is permitted to flow by the valve  54 , is indicated by arrow heads at the ends of the respective passages  50 A- 50 S. As used herein, a first component is “downstream” of a second component if coolant flows to the first component from the second component during a single circulation loop of the flow circuit, with the flow circuit beginning at the outlet  52 B of the pump  52 . A first component is “upstream” of a second component if coolant flows from the first component to the second component in a single circulation loop of the flow circuit with the flow circuit beginning at the outlet  52 B of the pump  52 . 
     The valve  54  is a rotary valve in the embodiment shown, but may be any type of valve having at least three positions and capable of establishing the flow modes described herein. The valve  54  has an internal movable member  55  that can be controlled by the controller  60  to establish three different positions, as shown in  FIGS. 6-8 . Coolant flow through the valve  54  is represented by arrows FI for flow into the valve  54  and FO for flow out of the valve  54 . The movable member  55  is pivotable about a pivot pin  57 . In a first position, shown in  FIG. 6 , the member  55  blocks the outlets  54 B,  54 C so that coolant cannot flow through the valve  54 . No coolant is thus provided to the engine  16 . As shown in  FIG. 7 , the valve  54  can be rotated in the direction of arrow  59  to a second position in which coolant can flow through the valve  54  from the inlet  54 A to the outlet  54 B and thus to the cylinder head  20 . The valve  54  can be rotated in the direction of arrow  61  to a third position in which coolant can flow through the valve  54 , from the inlet  54 A to the outlet  54 C, as shown in  FIG. 8 . 
     Similarly, the valve  56  is a three-position valve and has an inlet  56 A, a first outlet  56 B and a second outlet  56 C. The inlet  56 A is connected to the EHRDHE  30  by the coolant passage  50 H of  FIG. 1 . The first outlet  56 B is connected to an engine heat exchanger  62  by the passage  50 J. The second outlet  56 C is connected to a transmission heat exchanger  64  by the coolant passage  50 I. The engine heat exchanger  62  is in fluid communication with engine oil in an oil pan  85 . Specifically, engine oil is routed through passages  53 A and  53 B between the engine oil heat exchanger  62  and the oil pan  85  to enable the temperature of the engine oil to be varied by heat transfer with the coolant in the engine heat exchanger  62 . The heat exchanger  62  may heat or cool the oil, depending on the relative temperatures of the engine oil and the coolant. Similarly, the transmission oil in the transmission  22  is in thermal communication with the coolant via passages  53 C,  53 D through which the transmission oil is routed between the transmission  22  and the transmission oil heat exchanger  64 . This enables the temperature of the transmission oil to be varied by heat transfer with the coolant in the transmission heat exchanger  64 . The heat exchanger  64  may heat or cool the transmission oil, depending on the relative temperatures of the transmission oil and the coolant. 
     The valve  56  is a rotary valve but may be any type of valve having at least three positions and capable of establishing the flow modes described herein. The valve  56  has an internal movable member  55 A that can be controlled by the controller  60  to establish three different positions as shown in  FIGS. 9-11 . The movable member  55 A is pivotable about a pin  57 A. The movable member  55 A has a first position, shown in  FIG. 9 , in which the member  55 A blocks only the outlet  56 C so that coolant can flow through the valve from the inlet  56 A to the outlet  56 B and thus to the engine heat exchanger  62 . The movable member  55 A has a second position, shown in  FIG. 10 , in which the member  55 A blocks only the outlet  56 B so that coolant can flow through the valve  56  from the inlet  56 A to the outlet  56 C and thus to the transmission heat exchanger  64 . The movable member  55 A also has a third position, shown in  FIG. 11 , in which neither of the outlets  56 B,  56 C is blocked, so that coolant can flow through the valve  56  from the inlet  56 A to both the outlet  56 B and the outlet  56 C and thereby to both the engine heat exchanger  62  and the transmission heat exchanger  64 . 
     Referring again to  FIG. 1 , the bypass valve  32  has an inlet  32 A connected to the exhaust pipe  28 , a first outlet  32 B connected to the EHRDHE  30  and a second outlet  32 C connected to the bypass conduit  34 . The bypass valve  32  is connected to the controller  60 , and may be configured as a simple butterfly valve with an internal member movable by the controller  60  to direct the exhaust flow from the inlet  32 A to the outlet  32 B in a heat exchange position, and to direct the exhaust flow from the inlet  32 A to the outlet  32 C in a bypass position. 
     In an alternative embodiment, the bypass valve  32  could be any self-regulating valve that opens and closes automatically in response to temperature. For example, the bypass valve  32  could open in response to an actuator, such as a thermal wax, which is in thermal communication with the coolant and adjusts the valve opening based on the temperature of the coolant and expansion or contraction of the wax which is in contact with the bypass valve  32 . The bypass valve  32  could be configured to open automatically at a predetermined coolant temperature. 
     The radiator valve  58  has a first inlet  58 A, a second inlet  58 B and an outlet  58 C. The outlet  58 C of the valve  58  is connected to the inlet  52 A of the pump  52  by the passage  50 R. An internal member  59  is movable, in response to control signals from the controller  60 , from a first position, shown in  FIG. 1  to a second position shown in  FIG. 5 . When the internal member  59  is in the first position, coolant can flow from the first inlet  58 A to the outlet  58 C and the second inlet  58 B is blocked. When the internal member  59  is in the second position, coolant can flow from both the first inlet  58 A and the second inlet  58 B to the outlet  58 C. With the radiator valve in the second position so that the second inlet  58 B unblocked, coolant flows through a radiator  70  included in the cooling system  14 . Specifically, when the radiator valve  58  is in the second position, coolant can flow from the radiator  70  through passage  50 Q. This in turn permits coolant to flow into the radiator  70  from passage  50 S. In contrast, when the internal member  59  is in the first position, with the second inlet  58 B blocked, coolant cannot flow through the radiator  70 , and coolant in the passage  50 S is stopped. 
     In an alternative embodiment, the radiator valve  58  could be any self-regulating valve that opens and closes automatically in response to temperature. For example, the internal member  59  could open in response to an actuator, such as a thermal wax, which adjusts the valve opening based on the temperature of the coolant and expansion or contraction of the wax which is in contact with the movable member  59 . The valve  58  could be configured so that the internal member  59  opens automatically at a predetermined coolant temperature. 
     The powertrain cooling system  14  also includes multiple temperature sensors operatively connected to the controller  60  to provide current temperature conditions in the powertrain  12 . For example, a first temperature sensor  80  is mounted to, or in, or is otherwise operatively connected to the cylinder head  20  such that the sensor  80  is in thermal communication with the cylinder head  20  and can provide sensor signals to the controller  60  indicative of a cylinder head temperature. The electrical wiring connecting the sensor  80  to the controller  60  is not shown for purposes of clarity in the drawings. 
     A second temperature sensor  82  is mounted to, or in, or is otherwise operatively connected to the engine block  18  such that the sensor  82  is in thermal communication with the engine block  18  and can provide sensor signals to the controller  60  indicative of an engine block temperature. The electrical wiring connecting the sensor  82  to the controller  60  is not shown for purposes of clarity in the drawings. 
     A third temperature sensor  84  is mounted to, or in, or is otherwise operatively connected to the oil pan  85  mounted to the engine block  18  such that the sensor  84  is in thermal communication with engine oil that collects in the oil pan  85  and can provide sensor signals to the controller  60  indicative of an engine oil temperature. The electrical wiring connecting the sensor  84  to the controller  60  is not shown for purposes of clarity in the drawings. 
     A fourth temperature sensor  86  is mounted to, or in, or is otherwise operatively connected to the transmission  22  such that the sensor  86  is in thermal communication with transmission oil within the transmission  22  and can provide sensor signals to the controller  60  indicative of a transmission oil temperature. The electrical wiring connecting the sensor  86  to the controller  60  is not shown for purposes of clarity in the drawings. 
       FIG. 1  shows the cooling system  14  in a first cooling mode appropriate for a time period immediately after a cold start of the vehicle  10 . In the first cooling mode, the valve  54  is in the first position of  FIG. 6  such that fluid flow is not permitted through the valve  54 . Because the vehicle  10  has just been started, the coolant will likely be relatively cold, at less than a predetermined coolant temperature at which the radiator valve  58  opens. Accordingly, the radiator valve  58  will be in the closed position, and coolant flow will not be permitted through the radiator  70 . An algorithm stored in a processor of the controller  60  is configured so that the controller  60  will open the radiator valve  58  when the temperature of the coolant is above a predetermined coolant temperature. The coolant temperature may be indicated by association with the engine block temperature determined by the sensor  82 . The coolant temperature at which the radiator valve  58  opens may be indicative of an engine oil temperature and a transmission oil temperature above a predetermined maximum oil temperature. Accordingly, the radiator valve  58  opens to allow the coolant to flow through the radiator  70  only after the engine oil and the transmission oil are sufficiently warmed. 
     In the first cooling flow mode of  FIG. 1 , the bypass valve  32  is in the heat exchange position, and the valve  56  is in the first position. However, because the valve  54  is in the first position, cooling flow is stopped throughout the cooling system. Without circulation of the coolant, the cylinder head  20 , the engine block  18 , the engine oil and the transmission oil will all increase in temperature during this mode. 
     When the first temperature sensor  80  indicates that the temperature of the cylinder head  20  is greater than a first predetermined temperature, and the second temperature sensor  82  indicates that the temperature of the engine block  18  is less than a second predetermined temperature, the controller  60  will establish a second cooling flow mode by placing the valve  54  in the second position of  FIG. 7  to permit coolant to flow through the cylinder head  20  as indicated in  FIG. 2 . The first predetermined temperature is selected as an optimal cylinder head temperature. The second predetermined temperature is selected as an optimal engine block temperature. The valves  32  and  56  remain in the same positions as in the first cooling flow mode. The radiator valve  58  is also in the closed position, because the cylinder head temperature at which the valve  54  is placed in the second position is associated with an engine oil temperature and coolant temperature significantly less than that at which the valve  58  is moved to the open position. 
     With the valve  54  in the second position, pumped coolant flows through the cylinder head  20 , to the heater  23 , through the EHRDHE  30 , and through the engine heat exchanger  62  through passages  50 A,  50 B,  50 E,  50 F,  50 G,  50 H,  50 J,  50 K and  50 R. In this flow mode, the coolant will extract heat from the cylinder head  20 , provide heat at the heater  23 , pickup additional heat in the EHRDHE  30 , and provide heat at the engine heat exchanger  62  to heat the engine oil in the oil pan  85 . The transmission oil is not initially heated by the transmission heat exchanger  64 , as coolant does not flow to the transmission heat exchanger  64  at the outset of the second cooling flow mode. However, once the engine oil is heated to a predetermined temperature, the second three-position valve  56  can be controlled to move to the second position of  FIG. 10  so that coolant flows to the transmission heat exchanger  64  to heat the transmission oil. The valve  56  is controlled based on temperatures indicated by the temperature sensors  84 ,  86  so the engine oil and the transmission oil are heated in stages during the second cooling flow mode to provide maximal friction reduction benefits. 
     During the second cooling flow mode, the controller  60  continues to receive sensor signals from the temperature sensors indicative of sensed temperature conditions as described above. When the second temperature sensor  82  indicates that the temperature of the engine block  18  is greater than the second predetermined temperature, the controller  60  places the valve  54  in the third position, so that coolant flows to the engine block  18  and then to the cylinder head  20  in a U-formation through the passages  50 D and  50 E. The internal passages in the engine block  18 , represented by passage  50 D, are in continuous fluid communication with the internal passages of the cylinder head  20 , represented by passage  50 E creating a U-formation. It should be appreciated that the internal passages in the engine block  18  and the internal passages in the cylinder head  20  may be configured to be in fluid communication with one another in formations other than a U-formation. That is, the passages  50 D,  50 E may be configured in other than a U-formation. 
     When the valve  54  is in the second position of  FIGS. 2 and 7 , coolant in the passage  50 D is relatively stagnant, and is not affected by the coolant flow through the passage  50 E. Coolant flow through the passage  50 D with the valve  54  in the third position will force coolant to flow to passage  50 E and then to passage  50 F. The valve  32  remains in the exhaust heat recovery position. 
     During the third cooling flow mode, the valve  56  is controlled to establish staged heating of the engine oil and the transmission oil by moving between the first and second positions.  FIG. 3  shows one of these stages, with the valve  56  in the second position. Once optimum oil temperatures are reached, the valve  56  is moved to the third position of  FIG. 11 , as shown in  FIG. 4 , so that coolant is provided to both the engine heat exchanger  62  and the transmission heat exchanger  64  simultaneously to maintain oil temperature at the optimal, predetermined oil temperature via the heat exchangers  62 ,  64 . Coolant thus flows in a circuit in the third cooling flow mode, through the engine block  18 , the cylinder head  20 , the heater  23 , the EHRDHE  30 , and either or both of the engine heat exchanger  62  and the transmission heat exchanger  64  through passages  50 A,  50 C,  50 D,  50 E,  50 F,  50 G,  50 H,  50 I,  50 J,  50 K,  50 P and  50 R. 
     Exhaust heat recovery and coolant flow to the engine heat exchanger  62  and the transmission heat exchanger  64  continues until oil temperatures are consistent with maximum frictional benefits. Once the temperature sensors  84 ,  86  indicate that a predetermined maximum oil temperature at which maximum frictional benefits are achieved has been reached, a fourth cooling flow mode is established as shown in  FIG. 5 , as the valve  32  is moved to a bypass position and the radiator valve  58  is moved to an open position. The controller  60  moves the valve  58  to an open position when a coolant temperature consistent with the maximum oil temperatures is reached, with the coolant temperature being determined by the controller  60  based on engine block temperature. Coolant can then flow through the radiator  70  to exhaust additional heat. The valve  54  remains in the third position and the valve  56  remains in its third position. In the fourth cooling flow mode, coolant flows in a circuit through passages  50 A,  50 C,  50 D,  50 E, splitting through  50 F and  50 S. Flow from passage  50 F continues through the heater  23 , through passage  50 G, through the EHRDHE  30  (which the exhaust gas bypasses through conduit  34 ), is split through passage  50 I and  50 J, flows through passage  50 P or  50 K and then to  50 R. The coolant that split to passage  50 S flows through the radiator  70  to passage  50 Q and through the radiator valve  58  to the passage  50 R and back through the pump  52 . 
     A method of cooling a powertrain  12  that has an engine  16  with a cylinder head  20  and an engine block  18  thus includes controlling a first three-position valve  54  to a first position to block coolant flow to the engine block  18  when a temperature of the cylinder head  20  is less than a first predetermined temperature. The method further includes controlling the first three-position valve  54  to a second position to direct the coolant flow to the cylinder head  20  and block coolant flow from the engine block  18  when the temperature of the cylinder head  20  is greater than the first predetermined temperature and a temperature of the engine block  18  is less than a second predetermined temperature The method then includes controlling the first three-position valve  54  to a third position to direct the coolant flow to both the cylinder head  20  and the engine block  18  when the temperature of the engine block  18  is greater than the second predetermined temperature. 
     The method may include controlling a second three-position valve  56  that is downstream of the engine  16  to a first position to direct the coolant flow to an engine heat exchanger  62  when an engine oil temperature is less than a predetermined engine oil temperature. The second three-position valve  56  can then be controlled to a second position to direct the coolant flow to a transmission heat exchanger  64  when a transmission oil temperature is less than a predetermined transmission oil temperature and the engine oil temperature is greater than the predetermined engine oil temperature. The method may then include controlling the second three-position valve  56  to a third position to direct the coolant flow to both the engine heat exchanger  62  and the transmission heat exchanger  64  when the transmission oil temperature is greater than a predetermined transmission oil temperature and the engine oil temperature is greater than the predetermined engine oil temperature. The predetermined transmission oil temperature may be the same as the predetermined engine oil temperature. 
     Additionally, an exhaust heat recovery bypass valve  32  may be controlled under the method to direct engine exhaust so that it is in thermal communication with the coolant flow when the second three-position valve  56  is in the first position or in the second position. The exhaust heat recovery bypass valve  32  may be controlled so that the engine exhaust bypasses thermal communication with the coolant flow when the second three-position valve  56  is in the third position. A radiator valve  58  may be positioned in the coolant flow downstream of the engine heat exchanger  62  and the transmission heat exchanger  64 , upstream of an inlet  52 A of the coolant pump  52 , and downstream of a radiator  70 . Under the method, the valve  58  may be controlled to maintain a closed position in which coolant flow from the radiator  70  is blocked from the inlet  52 A of the pump  50 , shown in  FIG. 1 , thereby stopping coolant flow through the radiator  70 . The valve  58  may be controlled to maintain an open position, in which coolant flow from the radiator  70  is permitted through the radiator valve  58  to the inlet  52 A of the coolant pump  52 . The radiator valve  58  may be configured to permit coolant flow from the engine heat exchanger  62  and the transmission heat exchanger  64  to pass through the valve  58  in both the closed position and the open position. 
     While the best modes for carrying out the many aspects of the present teachings have been described in detail, those familiar with the art to which these teachings relate will recognize various alternative aspects for practicing the present teachings that are within the scope of the appended claims.