Method and system for controlling EGR rate in diesel engines

摘要

A method and system for controlling EGR rate of an internal combustion engine. The engine has an intake throttle for controlling mass flow to an intake of the engine and an EGR valve for controlling flow from the exhaust of the engine back to the intake of the engine along with air passing through the intake throttle. The method includes measuring a mass air flow passing to the intake throttle and a desired mass air flow. An error signal is produced representative of a difference between the measure mass air flow and the desired mass air flow. A pair of control signals is produced in response to such produced error signal. One of the pair of control signals is used to adjust the intake throttle to control mass air flow through such intake throttle. The other one of the pair of control signals is used to adjust EGR flow through the EGR valve. The pair of control signals operate the intake throttle and the EGR valve to drive the error signal towards a null. In one embodiment, the one of the control signals used to adjust the EGR valve is used to provide such adjustment only when the intake throttle is in a position to provide substantially maximum mass air flow through such intake throttle to the intake of the engine. In one embodiment the pair of control signals operate to drive the throttle to a closed position only when such error signal is unable to be driven towards the null solely from adjustment by the EGR valve. In one embodiment, the engine includes a turbocharger having a compressor and a turbine coupled to the compressor. A portion of engine exhaust is directed to the EGR valve and another portion of the engine exhaust is directed to the turbine. The one of the control signals adjusting the EGR valve adjusts such portions. The portion of the engine exhaust to the turbine contributes to the mass air flow via the compressor. The mass air flow from the compressor passes to the intake throttle and wherein the intake throttle adjustment adjusts the mass air flow.