Abstract:
A first loop contains engine coolant passageways ( 28, 30 ) and a first radiator ( 34 ). A second loop contains a first EGR cooler ( 48 ). A third loop contains a second EGR cooler ( 50 ), a second radiator ( 36 ), a charge air cooler ( 26 LP), a first valve ( 66 ), and a second valve ( 64 ). Valve ( 64 ) apportions coolant flow entering an inlet ( 64 A) to parallel flow paths, one including second radiator ( 36 ) and the other being a bypass around radiator ( 36 ). The apportioned flows merge into confluent flow to both an inlet of charge air cooler ( 26 LP) and a first inlet ( 66 B) of valve ( 66 ). Valve ( 66 ) has an outlet ( 66 C) communicated to an inlet of second EGR cooler ( 50 ). The first condition of valve ( 66 ) closes a second inlet ( 66 A) to coolant flowing toward both the second inlet ( 66 A) and inlet ( 64 A) while opening inlet ( 66 B) to outlet ( 66 C). The second condition of valve ( 66 ) opens second inlet ( 66 A) to coolant flowing toward second inlet ( 66 A) and inlet ( 64 A) of the valve ( 64 ) while closing first inlet ( 66 B) of valve ( 66 ) to outlet ( 66 C) of valve ( 66 ).

Description:
TECHNICAL FIELD 
       [0001]    This disclosure relates to internal combustion engines, especially diesel engines in motor vehicles, that use exhaust gas recirculation (EGR) as a component of tailpipe emission control strategy. 
       BACKGROUND OF THE DISCLOSURE 
       [0002]    A typical EGR system of an engine includes one or more EGR valves for controlling the flow of engine exhaust gas from the engine&#39;s exhaust system to the engine&#39;s intake system to meter an appropriate amount of exhaust gas into fresh air passing through the intake system where the air supports combustion of fuel in the engine&#39;s cylinders. The metered exhaust gas in effect dilutes the air so that in-cylinder temperature rise resulting from combustion is limited from that which would occur in the absence of such dilution. As a consequence, the quantity of oxides of nitrogen (NOx) in the exhaust gas that results from combustion is also limited. 
         [0003]    Some EGR systems, especially those designed for compression ignition (i.e. diesel) engines, have one or more heat exchangers for cooling recirculated exhaust gas. Cooling of the exhaust gas can further limit the generation of NOx. 
         [0004]    It is recognized in the industry that cooling of recirculated exhaust gas creates the potential for condensation of certain gaseous constituents of the exhaust gas. Control of condensation may be a factor in the design of various engine systems. 
       SUMMARY OF THE DISCLOSURE 
       [0005]    This disclosure relates to an internal combustion engine comprising engine structure comprising engine cylinders within which fuel is combusted to operate the engine and coolant passageways, an intake system for conveying air to the engine cylinders to support fuel combustion and comprising a charge air cooler for cooling conveyed air, an exhaust system for conveying combustion-created exhaust gas from the cylinders, an EGR system for recirculating some exhaust gas from the exhaust system successively through a first heat exchanger and a second heat exchanger to the intake system for entrainment with air being conveyed to the cylinders and a cooling system for circulating liquid coolant in multiple loops and comprising first and second radiators. 
         [0006]    A first of the loops comprises the coolant passageways where heat from the engine structure is transferred to coolant and the first radiator where heat in coolant that has passed through the coolant passageways is rejected. 
         [0007]    A second of the loops comprises one of the first and second heat exchangers. 
         [0008]    A third of the loops comprises the other of the first and second heat exchangers, the second radiator, the charge air cooler, a first valve that is selectively operable to first and second conditions, and a second valve that is operable to selectively apportion coolant flow entering an inlet of the second valve to parallel flow paths, one of which includes the second radiator and the other of which bypasses the second radiator, and which merge into confluent flow downstream of the second radiator to convey coolant to both an inlet of the charge air cooler and a first inlet of the first valve. The first valve has an outlet communicated an inlet of the other of the first and second heat exchangers. 
         [0009]    The first condition of the first valve closes a second inlet of the first valve to coolant flowing toward both the second inlet of the first valve and the first inlet of the second valve while opening the first inlet of the first valve to the outlet of the first valve. 
         [0010]    The second condition of the first valve opens the second inlet of the first valve to coolant flowing toward the second inlet of the first valve and the first inlet of the second valve while closing the first inlet of the first valve to the outlet of the first valve. 
         [0011]    The disclosure also relates to a circuit for cooling both exhaust gas being recirculated through an EGR system of an internal combustion engine and charge air for supporting combustion in engine combustion chambers. 
         [0012]    The circuit comprises a first loop comprising coolant passageways in engine structure containing where coolant absorbs heat from the engine structure and a first radiator where heat absorbed by coolant is rejected, a second loop comprising a first EGR cooler, and a third loop comprising a second EGR cooler, a second radiator, a charge air cooler for cooling charge air entering the engine, a first valve that is selectively operable to first and second conditions, and a second valve that is operable to selectively apportion coolant flow entering an inlet of the second valve to parallel flow paths, one of which includes the second radiator and the other of which bypasses the second radiator, and which merge into confluent flow downstream of the second radiator to convey coolant to both an inlet of the charge air cooler and a first inlet of the first valve. The first valve has an outlet communicated an inlet of the second EGR cooler. 
         [0013]    The first condition of the first valve closes a second inlet of the first valve to coolant flowing toward both the second inlet of the first valve and the first inlet of the second valve while opening the first inlet of the first valve to the outlet of the first valve. 
         [0014]    The second condition of the first valve opens the second inlet of the first valve to coolant flowing toward the second inlet of the first valve and the first inlet of the second valve while closing the first inlet of the first valve to the outlet of the first valve. 
         [0015]    The disclosure also relates to a method for cooling both exhaust gas being recirculated through an EGR system of an internal combustion engine and charge air for supporting combustion in engine combustion chambers. 
         [0016]    The method comprises: circulating liquid coolant in a first loop comprising coolant passageways in engine structure where heat from the engine structure is transferred to coolant and a first radiator where heat in coolant that has passed through the coolant passageways is rejected; circulating liquid coolant in a second loop comprising a first EGR cooler; and circulating liquid coolant in a third loop comprising a second EGR cooler, a second radiator, a charge air cooler for cooling charge air entering the engine, a selectively operable first valve, and a second valve for selectively apportioning coolant flow entering an inlet of the second valve to parallel flow paths, one of which includes the second radiator and another of which bypasses the second radiator, and which merge into confluent flow downstream of the second radiator to convey coolant to both an inlet of the charge air cooler and a first inlet of the first valve, the first valve having an outlet communicated an inlet of the second EGR cooler. 
         [0017]    The method further comprises selectively operating the first valve to a first condition closing a second inlet of the first valve to coolant flowing toward both the second inlet of the first valve and the first inlet of the second valve while opening the first inlet of the first valve to the outlet of the first valve, and to the second condition opening the second inlet of the first valve to coolant flowing toward the second inlet of the first valve and the first inlet of the second valve while closing the first inlet of the first valve to the outlet of the first valve, and operating the second valve to selectively apportion coolant flow entering the inlet of the second valve to the parallel flow paths. 
         [0018]    The foregoing summary is accompanied by further detail of the disclosure presented in the Detailed Description below with reference to the following drawings that are part of this disclosure. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0019]      FIG. 1  is a schematic diagram showing a first embodiment of the disclosed system in an engine. 
           [0020]      FIG. 2  is a schematic diagram showing a second embodiment of the disclosed system in an engine. 
           [0021]      FIG. 3  is a schematic diagram showing a third embodiment of the disclosed system in an engine. 
       
    
    
     DETAILED DESCRIPTION 
       [0022]      FIG. 1  shows a diesel engine  10  that comprises structure  12  containing engine cylinders  14  within which combustion of fuel occurs to operate the engine, such structure typically comprising a cylinder block  16  and one or more cylinder heads  18  depending on the particular type of engine block (such as an I-engine or a V-engine block). Engine  10  also comprises an air intake system  20  for conveying fresh air/EGR to cylinders  14  where the air supports the combustion of fuel. Engine  10  further comprises an exhaust system  22  for conveying combustion-created exhaust gas from cylinders  14  to a tailpipe through which the gas is discharged. 
         [0023]    Engine  10  also comprises a turbocharger  24  shown as a two-stage turbocharger having a high-pressure turbine  24 HPT and a low-pressure turbine  24 LPT both operated by exhaust gas from cylinders  14  for operating respective high-pressure and low-pressure compressors  24 HPC and  24 LPC that draw fresh air into intake system  20  to create charge air for the engine. Because the compression of the air elevates its temperature, the compressed air leaving the low-pressure compressor stage flows first through a low-pressure charge air cooler (LPCAC)  26 LP (sometimes also called an inter-stage cooler or ISC) where some heat is rejected before the charge air is further compressed by high-pressure compressor  24 HPC. A high-pressure charge air cooler (HPCAC)  26 HP cools the air coming from the high-pressure compressor stage before it is delivered to a mixer where it may mix with recirculated exhaust gas before finally entering cylinders  14  through an intake manifold. 
         [0024]    Engine  10  comprises a liquid cooling system that includes a system of coolant passageways  28  in block  16  and a system of coolant passageways  30  in head  18 . Liquid coolant is circulated through the cooling system by a pump  32 , which by way of example is an engine-driven coolant pump. The circulating coolant absorbs engine heat as it passes through the systems of passageways  28 ,  30  and rejects absorbed heat to air passing through a high-temperature (HT) radiator  34 . When engine  10  is the powerplant of a motor vehicle such as a large truck, radiator  34  is typically a liquid-to-air heat exchanger. The cooling system also comprises a low-temperature (LT) radiator  36  that may also be a liquid-to-air heat exchanger. 
         [0025]    Coolant circulates through various loops that include passageways in block  16  and/or head  18  but do not include either radiator  34  or  36 . Loops  38 ,  40 , and  42  are examples of such loops. An expansion tank  44  can collect overflow coolant from various locations in the cooling system, such as those shown, and provide for return of coolant to a suction inlet  32 S of pump  32 . 
         [0026]    The flow in any flow loop passing through HT radiator  34  leaves HT radiator  34  at a temperature T HTR . 
         [0027]    Engine  10  also comprises an EGR system for recirculating some exhaust gas from exhaust system  22  in succession through a first heat exchanger  48 , sometimes called a high-temperature (HT) EGR cooler, and a second heat exchanger  50 , also sometimes called a low-temperature (LT) EGR cooler, to the mixer in intake system  20  for entrainment with the charge air flowing to cylinders  14 . An EGR valve  52  controls the recirculation flow. Although the recirculation flow path and the pierce points to intake system  20  and to exhaust system  22  are not specifically shown in  FIG. 1 , the pierce point to exhaust system  22  can be upstream of high-pressure turbine  24 HPT and the pierce point to intake system  20  can be downstream of high-pressure compressor  24 HPC. The recirculation flow path may comprise EGR valve  52 , HT EGR cooler  48  and LT EGR cooler  50  in that order from the pierce point to exhaust system  22  to the pierce point to intake system  20 . The overflow coolant path from (LPCAC)  26 LP that is shown passing through EGR valve  52  passes through a passageway in the EGR valve body to provide some cooling for the EGR valve which happens to be close-coupled to an engine exhaust manifold. 
         [0028]    Pump  32  pumps coolant in parallel paths through HT EGR cooler  48 , coolant passageways  28 , and coolant passageways  30 . Flows through those parallel paths confluently enter an inlet  54  of a temperature-controlled valve  56 , such as a thermostat, that comprises two outlets  58 ,  60 . Outlet  58  is in fluid communication with the suction inlet  32 S of pump  32 , and outlet  60  is in fluid communication with an inlet  62  of HT radiator  34 . HT radiator  34  has an outlet  63  also in communication with suction inlet  32 S. Coolant for a heater core  61  that heats the interior of an occupant compartment in a motor vehicle that is powered by engine  10  is shown being supplied from the outlet of HT EGR cooler  48 , but could be supplied from any other source that provides suitably high temperature. 
         [0029]    An outlet  32 P outlet of pump  32  is in fluid communication both with an inlet  64 A of a CCV valve  64  and with an inlet  66 A of a switch valve  66 . CCV valve  64  comprises an outlet  64 B that is in fluid communication with an inlet  68  of LT radiator  36  and an outlet  64 C that is in fluid communication both with an inlet  66 B of switch valve  66  and an inlet of low-pressure charge air cooler  26 LP. LT radiator  36  has an outlet  70  that is in fluid communication both with inlet  66 B of switch valve  66  and with the inlet of low-pressure charge air cooler  26 LP. 
         [0030]    Switch valve  66  has an outlet  66 C that is in fluid communication with an inlet of LT EGR cooler  50 . Outlets of LT EGR cooler  50  and low-pressure charge air cooler  26 LP are in fluid communication with suction inlet  32 S of pump  32 . 
         [0031]    Switch valve  66  is selectively operable to a first state in which inlet  66 A communicates with outlet  66 C while inlet  66 B is closed to inlet  66 A and outlet  66 C, and to a second state in which inlet  66 B communicates with outlet  66 C while inlet  66 A is closed to inlet  66 B and outlet  66 C. 
         [0032]    Before engine  10  attains operating temperature, temperature-controlled valve  56  blocks flow of coolant from block  16  and head  18  to HT radiator  34  and returns the flow directly to suction inlet  32 S of pump  32 . When engine  10  attains operating temperature, valve  56  forces flow of coolant from block  16  and head  18  through HT radiator  34  before the flow returns to suction inlet  32 S. 
         [0033]    Coolant leaving HT radiator  34  via outlet  63  flows to pump suction inlet  32 S, through pump  32 , to inlet  66 A of switch valve  66  and inlet  64 A of CCV valve  64 . While there may be some differences in actual coolant temperature at various points along this flow path, coolant temperature at any point may be considered to be T HTR , as marked in  FIG. 1 . An orifice OR provides a proper flow rate for balancing flow along this flow path in this relation to other coolant system flows. 
         [0034]    CCV valve  64  can apportion coolant entering inlet  64 A between two parallel branches from the respective outlets  64 B,  64 C. The branch from outlet  64 B contains LT radiator  36  and the other branch from outlet  64 C is a bypass around LT radiator  36 . CCV valve  64  controls the temperature of coolant flowing through LT EGR cooler  50  for managing exhaust gas condensation. 
         [0035]    CCV valve  64  is controlled to apportion the flows through the respective branches as a function of certain variables related to air, coolant, and exhaust gas properties. The variables that are used may be measured in any suitably appropriate way such as by sensors (real and/or virtual) and/or estimated or inferred using suitable models. Any particular control strategy will depend on the particular engine and particular objective(s) to be achieved at various engine operating conditions. Different strategies may be used in different engines and to accomplish different control objectives. CCV valve  64  can function to apportion the branch flows such that 100% of the entering flow passes through one branch and 0% through the other, and vice versa. It can also divide the flows such that some percentage less than 100% of the entering flow passes through one branch and the remainder through the other branch. 
         [0036]    When switch valve  66  is placed in its first state (inlet  66 A communicating with outlet  66 C while inlet  66 B is closed to inlet  66 A and outlet  66 C), the system of  FIG. 1  functions in the following manner. 
         [0037]    Coolant entering switch valve  66  from pump  32  has a temperature T HTR . The temperature of coolant entering the inlet of low-pressure charge air cooler  26 LP is designated T MIX  and that temperature is controlled by CCV valve  64 . 
         [0038]    If CCV valve  64  closes outlet  64 B to flow, the entire flow entering inlet  64 A exits via outlet  64 C and passes through low-pressure charge air cooler  26 LP, causing the temperature of coolant entering charge air cooler  26 LP to be the temperature T HTR . 
         [0039]    The temperature of coolant coming from outlet  70  of LT radiator  36  is marked T LTR . The quantity of coolant heat that is being rejected at LT radiator  36  determines how much lower the temperature T LTR  is than the temperature T HTR . If CCV valve  64  is closing outlet  64 C to flow, the entire flow entering inlet  64 A exits via outlet  64 B and passes through LT radiator  36  before entering low-pressure charge air cooler  26 LP, causing the temperature T MIX  of coolant entering charge air cooler  26 LP to equal the temperature T LTR . 
         [0040]    If CCV valve  64  is apportioning the entering flow between outlets  64 B and  64 C, one portion of the flow is cooled by LT radiator  36  while the remainder is not. In this instance the temperature T MIX  of coolant entering charge air cooler  26 LP will be lower than the temperature T HTR  but higher than the temperature T LTR , with the specific temperature being a function of the extent to which CCV valve  64  is apportioning the flow through the respective branches. 
         [0041]    When switch valve  66  is placed in its second state in which inlet  66 B communicates with outlet  66 C while inlet  66 A is closed to inlet  66 B and outlet  66 C, coolant entering switch valve  66  has the same temperature T MIX  as coolant entering low-pressure charge air cooler  26 LP. With the value of T MIX  being controlled by CCV valve  64 , the temperature of coolant entering both charge air cooler  26 LP and LT EGR cooler  50  is controlled by controlling CCV valve  64  in the same manner as described above. 
         [0042]    Placing switch valve  66  in its second state, allows switch valve  66  to concurrently control both EGR cooling and charge air cooling. When EGR needs less cooling, such as to mitigate EGR condensation, placing switch valve  66  in its first state allows coolant having temperature T HTR  to pass through LT EGR cooler  50  for mitigating EGR condensation, while the temperature T MIX  of coolant entering charge air cooler  26 LP can still be controlled by CCV valve  64  to cause the temperature of coolant passing through charge air cooler  26 LP to be lower than that of coolant passing through LT EGR cooler  50  continuing the greater cooling of charge air that increases charge air density, and hence improves performance of turbocharger  24 . 
         [0043]      FIG. 1  shows HT EGR cooler  48  to be in parallel flow relationship to passageways  28 ,  30  before the parallel flows merge to confluently pass through temperature-controlled valve  56  before returning either directly or through radiator  34  to suction inlet  32 S of pump  32  as determined by temperature of coolant leaving block  16 /head  18  (that temperature corresponding to engine operating temperature). 
         [0044]    The flow from pump outlet  32 P through passageways  28 ,  30  and either directly, or through HT radiator  34 , back to suction inlet  32 S may be considered a first flow loop. 
         [0045]    The flow from pump outlet  32 P through HT EGR cooler  48  and either directly, or through HT radiator  34 , back to suction inlet  32 S as controlled by valve  56 , may be considered a second flow loop. 
         [0046]    Flow from pump outlet  32 P to valves  64 ,  66 , and subsequently as controlled by valves  64 ,  66  before returning to suction inlet  32 S may be considered a third flow loop. 
         [0047]      FIG. 2  shows an embodiment in which the same reference numerals designate the same elements shown and described in connection with  FIG. 1 .  FIG. 2  differs from  FIG. 1  in that the flow to HT EGR cooler  48  has passed through engine passageways  28 ,  30  rather than coming directly from pump outlet  32 P. Consequently, when engine  10  is running at operating temperature, hotter coolant is delivered to HT EGR cooler  48  than when coolant is supplied directly from pump outlet  32 P. Flow to CCV valve  64  and switch valve  66  continues to come directly from pump outlet  32 P. Coolant for heater core  61  is supplied from the outlets of engine passageways  28 ,  30 . 
         [0048]      FIG. 3  shows an embodiment in which the same reference numerals designate the same elements shown and described in connection with  FIG. 1 .  FIG. 3  differs from  FIG. 1  in that the flows to HT EGR cooler  48  and to CCV valve  64  and switch valve  66  have passed through passageways  28 ,  30  rather than coming directly from pump outlet  32 P. Consequently, when engine  10  is running at operating temperature, hotter coolant is delivered to HT EGR cooler  48  and to CCV valve  64  and switch valve  66  than when coolant is supplied directly from pump outlet  32 P. Coolant for heater core  61  is supplied from the outlets of engine passageways  28 ,  30 .