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A catalyst bed temperature of an aftertreatment device is maintained and the operational regime for stable and smokeless rich combustion is expanded by use of a dual loop exhaust gas recirculation system. Under light load conditions, at least a portion of the exhaust gas is recirculated through a re

A catalyst bed temperature of an aftertreatment device is maintained and the operational regime for stable and smokeless rich combustion is expanded by use of a dual loop exhaust gas recirculation system. Under light load conditions, at least a portion of the exhaust gas is recirculated through a relatively high pressure exhaust gas recirculation loop, wherein there is no substantial reduction in recirculated exhaust gas temperature or pressure. When operating in relatively medium or higher load operating regimes of the engine, at least a portion of the exhaust gas is passed through a relatively low pressure recirculation mode in which work is extracted from the recirculated gas by the turbine stage of a turbocharger and an exhaust gas recirculation cooler prior to reintroduction into the intake manifold of the engine.

대표청구항 ▼

What I claim is: 1. A method for operating a Diesel engine in two exhaust gas recirculation modes, said Diesel engine having at least one combustion chamber, an intake manifold and an exhaust manifold in respective fluid communication with the combustion chamber, and a turbocharger having a turbine

What I claim is: 1. A method for operating a Diesel engine in two exhaust gas recirculation modes, said Diesel engine having at least one combustion chamber, an intake manifold and an exhaust manifold in respective fluid communication with the combustion chamber, and a turbocharger having a turbine stage and a compressor stage, said turbine stage having an inlet port in fluid communication with said exhaust manifold and a discharge port in fluid communication with an exhaust gas aftertreatment device, and said compressor stage having an inlet port in fluid communication with a source of ambient air and a discharge port in fluid communication with said intake manifold, said method comprising: defining a low load portion of an operating regime of the engine in which a first exhaust gas recirculation mode is desired; defining a medium to high load portion of the operating regime of the engine in which a second exhaust gas recirculation mode is desired; sensing at least one contemporaneous engine operating parameter; determining a desirable one of said first and second defined exhaust gas recirculation modes in response to a sensed value of said at least one contemporary engine operating parameter; discharging exhaust gas from said at least one combustion chamber into said exhaust manifold; controllably dividing the exhaust gas into first and second portions in response to determining that said first defined exhaust gas recirculation mode is the desired exhaust gas recirculation mode; directing the first portion of the exhaust gas through an oxidation catalyst wherein the temperature of said first portion of the exhaust gas is maintained at a temperature sufficient to subsequently provide a mixture of the first portion of the exhaust gas and air in said intake manifold that has a temperature that enables stable combustion in response to determining that said engine is operating in said defined low load portion of the engine operating regime; subsequently directing the first portion of the exhaust gas to an exhaust gas recirculation flow control valve; discharging the first portion of the exhaust gas from the exhaust gas recirculation flow control valve and into said intake manifold; mixing the first portion of the exhaust gas with air in said intake manifold; inducting the mixed first portion of the exhaust gas and air into said at least one combustion chamber of the engine; directing the second portion of the exhaust gas through the turbine stage of said turbocharger, said exhaust gas aftertreatment device, and subsequently into an ambient environment when said engine is operating in said defined low load portion of the engine operating regime; directing all of the exhaust gas from said exhaust manifold through the turbine stage of said turbocharger and into said exhaust gas aftertreatment device in response to determining that said engine is operating in one of said defined medium to high load portion of the operating regime of the engine; discharging the exhaust gas from said exhaust gas aftertreatment device; subsequently controllably dividing the exhaust gas discharged from the exhaust gas aftertreatment device into principal and subordinate portions; directing the principal portion of said exhaust gas through an exhaust gas recirculation cooler; directing the principal portion of said exhaust gas through an exhaust gas recirculation flow control valve; discharging the principal portion of said exhaust gas into an intake conduit in fluid communication with the intake port of the compressor stage of said turbocharger; controllably mixing the principal portion of the exhaust gas with air; directing the mixed principal portion of the exhaust gas and air into the intake port of the compressor stage of said turbocharger; compressing the mixed principal portion of the exhaust gas and air; passing at least a portion of said compressed mixture of the principal portion of exhaust gas and air through an intercooler wherein the temperature of said portion is controlled so that when subsequently remixed with any remaining portion of the compressed mixture of the principal portion of exhaust gas and air, the resultant mixture will have a temperature below a temperature at which significant soot is formed when said engine is operating in said defined medium to high load portion of the engine operating regime; remixing said portion of said compressed mixture of the principal portion of exhaust gas and air passed through said intercooler with any remaining portion of said compressed mixture of the principal portion of exhaust gas and air; introducing the remixed compressed mixture of the principal portion of the exhaust gas and air into the intake manifold of said engine; inducting the compressed mixture of the principal portion of the exhaust gas and air into said at least one combustion chamber of the engine; and discharging the subordinate portion of said exhaust gas into the ambient environment. 2. The method for operating a Diesel engine in two exhaust gas recirculation modes, as set forth in claim 1, wherein said sensing at least one contemporaneous engine operating parameter includes sensing at least one parameter selected from the group consisting of engine speed, crank angle, engine load, intake manifold temperature, engine coolant temperature, exhaust gas temperature, exhaust gas aftertreatment device temperature, fuel injection volume, accelerator angle, and cylinder pressure. 3. The method for operating a Diesel engine in two exhaust gas recirculation modes, as set forth in claim 1, wherein said determining a desirable one of said first and second defined exhaust gas recirculation modes in response to a sensed value of said at least one contemporary engine operating parameter includes determining the desirable exhaust gas recirculation mode based on the sensed value of the coolant temperature. 4. The method for operating a Diesel engine in two exhaust gas recirculation modes, as set forth in claim 1, wherein said determining a desirable one of said first and second defined exhaust gas recirculation modes in response to a sensed value of said at least one contemporary engine operating parameter includes determining the desirable exhaust gas recirculation mode based on the sensed value of the intake manifold temperature. 5. The method for operating a Diesel engine in two exhaust gas recirculation modes, as set forth in claim 1, wherein said determining a desirable one of said first and second defined exhaust gas recirculation modes in response to a sensed value of said at least one contemporary engine operating parameter includes determining the desirable exhaust gas recirculation mode based on the sensed value of one of exhaust gas temperature and exhaust gas aftertreatment device temperature. 6. The method for operating a Diesel engine in two exhaust gas recirculation modes, as set forth in claim 1, wherein said determining a desirable one of said first and second defined exhaust gas recirculation modes in response to a sensed value of said at least one contemporary engine operating parameter includes determining the desirable exhaust gas recirculation mode based on the sensed value of the maximum pressure sensed in said at least one combustion chamber during a combustion cycle of the engine. 7. The method for operating a Diesel engine in two exhaust gas recirculation modes, as set forth in claim 1, wherein said determining a desirable one of said first and second defined exhaust gas recirculation modes in response to a sensed value of said at least one contemporary engine operating parameter includes determining the desirable exhaust gas recirculation mode based on the sensed value of the rate of change in pressure within said at least one combustion chamber with respect to a change in crank angle. 8. The method for operating a Diesel engine in two exhaust gas recirculation modes, as set forth in claim 1, wherein said determining a desirable one of said first and second defined exhaust gas recirculation modes in response to a sensed value of said at least one contemporary engine operating parameter includes determining the desirable exhaust gas recirculation mode based on the sensed value of a change in the heat transfer rate within said at least one combustion chamber with respect to crank angle. 9. The method for operating a Diesel engine in two exhaust gas recirculation modes, as set forth in claim 1, wherein said engine includes an air intake system extending between the inlet port of said compressor stage of the turbocharger and said source of ambient air, said air intake system being adapted to control the flow of ambient air from said source to said inlet port of the compressor stage, and said method includes controllably regulating the amount of ambient air provided to the inlet port of said compressor stage. 10. The method for operating a Diesel engine in two exhaust gas recirculation modes, as set forth in claim 1, wherein said air intake system includes an air flow meter and said method includes measuring the flow rate of ambient air provided to said inlet port of the compressor stage. 11. The method for operating a Diesel engine in two exhaust gas recirculation modes, as set forth in claim 1, wherein said engine includes an intercooler interposed between the discharge port of the compressor stage of the turbocharger and the intake manifold of the engine, and said method includes controllably directing at least a portion of the compressed mixture of the principal portion of the exhaust gas and air through the intercooler after discharge from the compressor stage of the turbocharger and prior to discharge into the intake manifold of the engine. 12. A dual loop exhaust gas recirculation system for a diesel engine having at least one combustion chamber, an intake manifold and an exhaust manifold in respective fluid communication with the combustion chamber, and a turbocharger having a turbine stage and a compressor stage, said turbine stage having an inlet port in fluid communication with said exhaust manifold and a discharge port, and said compressor stage having an inlet port in fluid communication with a source of ambient air and a discharge port in fluid communication with said intake manifold, said dual loop exhaust gas recirculation system comprising: a high pressure exhaust gas recirculation loop having an oxidation catalyst with opposed intake and discharge ports, said intake port of the oxidation catalyst being in controlled fluid communication with said exhaust manifold of the engine, and an exhaust gas recirculation flow control valve interposed between said discharge port of the oxidation catalyst and said intake manifold of the engine; a low pressure exhaust gas recirculation loop having an exhaust gas aftertreatment device with opposed intake and discharge ports, said intake port of the exhaust gas aftertreatment device being in direct fluid communication with the discharge port of the turbine section of said turbocharger, said discharge port of the exhaust gas aftertreatment device being in fluid communication with an exhaust conduit providing fluid communication with an ambient environment, and exhaust gas recirculation cooler having opposed intake and discharge ports, said intake port of the exhaust gas recirculation cooler being in controlled fluid communication with the discharge port of said exhaust gas aftertreatment device, and an exhaust gas recirculation flow control valve interposed between the discharge port of said exhaust gas recirculation cooler and the inlet port of the compressor stage of said turbocharger; and a control unit adapted to control intake manifold temperature by modulating the operation of said exhaust gas recirculation flow control valves in said high pressure and said low pressure exhaust gas recirculation loops to lower the temperature of a compressed mixture of recirculated exhaust gas and air prior to introduction into said intake manifold to a temperature at which soot formation is minimized during operation of said engine in predefined medium to high load operating regime and to maintain the temperature of recirculated exhaust gas introduced into said intake manifold at a temperature at which stable combustion is enabled during operation of said engine in a predefined low load operating regime. 13. The dual loop exhaust gas recirculation system, as set forth in claim 1, wherein said engine has an ambient air intake system, said ambient air intake system having an airflow meter in fluid communication with said source of ambient air and an airflow throttle valve interposed between said airflow meter and the inlet port of the compressor stage of said turbocharger. 14. The dual loop exhaust gas recirculation system, as set forth in claim 1, wherein said low pressure exhaust gas recirculation loop includes an intercooler interposed between the discharge port of the compressor stage of said turbocharger and said intake manifold of the engine. 15. The dual loop exhaust gas recirculation system, as set forth in claim 14, wherein said intercooler is adapted to selectively bypass at least a portion of fluid discharged from the discharge port of said compressor stage around a heat transfer portion of the intercooler and into the intake manifold of the engine without significantly altering the temperature of the bypassed fluid.