VVA CONTROL OF NOx IN A LOW AP AREA OF AN ENGINE OPERATING MAP

An internal combustion engine which comprises,

• engine structure comprising engine cylinders within which fuel is combusted to operate the engine,
• a turbocharger comprising at least one turbine for operating at least one compressor,
• an exhaust system comprising an exhaust manifold through which engine exhaust leaves the engine cylinders and is subsequently conveyed to an exhaust outlet,
• the at least one turbine being in downstream flow relation to the exhaust manifold and operated by engine exhaust,
• an intake system comprising an air inlet through which an air component for supporting combustion of fuel enters the intake system and an intake manifold through which a mixture comprising the air component and an engine exhaust component diverted from a point of diversion in the exhaust system to a point of mixing in the intake system enters the engine cylinders, the at least one compressor being in downstream flow relationship to the air inlet for causing pressure of the mixture in the intake manifold to be superatmospheric,
• cylinder intake valves for controlling admission of the mixture from the intake manifold into the engine cylinders,
• an EGR system for conveying the engine exhaust component of the mixture from the point of diversion to the point of mixing,
• an intake valve operating mechanism for varying the timing of operation of the cylinder intake valves during engine cycles, and
• a controller which, when the difference by which pressure in the exhaust manifold exceeds pressure in the intake manifold becomes less than a selected difference while the intake valve operating mechanism is closing the cylinder intake valves at a selected time in the engine cycle, while the EGR system is conveying the engine exhaust component of the mixture from the point of diversion to the point of mixing, and while a certain quantity of NOx is present in engine exhaust entering the exhaust manifold from the engine cylinders, then reduces the quantity of NOx present in engine exhaust entering the exhaust manifold below that certain quantity by causing the intake valve operating mechanism to close the cylinder intake valves earlier in the engine cycle than the selected time.

An internal combustion engine which comprises,

• engine structure comprising engine cylinders within which fuel is combusted to operate the engine,
• a turbocharger comprising at least one turbine for operating at least one compressor,
• an exhaust system comprising an exhaust manifold through which engine exhaust leaves the engine cylinders and is subsequently conveyed to an exhaust outlet,
• the at least one turbine being in downstream flow relation to the exhaust manifold and operated by engine exhaust,
• an intake system comprising an air inlet through which an air component for supporting combustion of fuel enters the intake system and an intake manifold through which a mixture comprising the air component and an engine exhaust component diverted from a point of diversion in the exhaust system to a point of mixing in the intake system enters the engine cylinders, the at least one compressor being in downstream flow relationship to the air inlet for causing pressure of the mixture in the intake manifold to be superatmospheric,
• cylinder intake valves for controlling admission of the mixture from the intake manifold into the engine cylinders,
• a camshaft having fixed cams set to open and close the cylinder intake valves at fixed times during an engine cycle;
• an EGR system for conveying the engine exhaust component of the mixture from the point of diversion to the point of mixing,
• a variable valve actuating mechanism which interacts with the fixed cams and the cylinder intake valves for advancing the closing time of the cylinder intake valves from the fixed closing time set by the fixed cams, and
• a controller which, when the difference by which pressure in the exhaust manifold exceeds pressure in the intake manifold becomes less than a selected difference while the variable valve actuating mechanism is idle and the cylinder intake valves close at the closing time set by the fixed cams, while the EGR system is conveying the engine exhaust component of the mixture from the point of diversion to the point of mixing, and while a certain quantity of NOx is present in engine exhaust entering the exhaust manifold from the engine cylinders, then reduces the quantity of NOx present in engine exhaust entering the exhaust manifold below that certain quantity by operating the variable valve actuating mechanism to cause the closing time of the cylinder intake valves to be advanced from the fixed closing time set by the fixed cams.