Method of controlling an internal combustion engine with a turbocharger

Abstract

An engine assembly comprising an internal combustion engine having a combustion chamber; an intake manifold for supplying air to the combustion chamber; a fuel injector for supplying fuel to the combustion chamber; an exhaust manifold for receiving exhaust gas released from the combustion chamber and a rotatable drive shaft, wherein combustion of fuel in air within the combustion chamber results in rotation of the drive shaft. The engine assembly further comprises a turbocharger system comprising a turbine and a compressor, wherein the turbine is configured to receive exhaust gas from the exhaust manifold, to recover energy from the exhaust gas, and to release the exhaust gas via a turbine outlet; and wherein the compressor is configured to receive energy from the turbine and thereby to compress air for use in combustion of fuel in the combustion chamber. An intake throttle valve is configured to selectively control a boost pressure by controlling supply of air to the intake manifold; and a bypass valve is configured to selectively divert exhaust gas from the exhaust manifold away from the turbine, wherein the bypass valve is controlled by the boost pressure. A controller is configured (a) to provide an intermediate value for desired valve position of the intake throttle valve based on a desired oxygen to fuel ratio; and (b) to output a final value for desired valve position of the intake throttle valve based on the intermediate value for desired valve position and an engine speed value.