Navistar International Transportation Corporation

Dale A Oehlerking

Terry G Wood

Titus J Iwaszkiewicz

James C McCandless

Milan E Zlock

An exhaust back pressure control system includes a valve in the exhaust outlet of a turbocharger of an internal combustion engine which is controlled by an engine control microcomputer. When the valve is moved toward a closed position, it restricts the exhaust flow, thereby increasing back pressure and friction within the engine by producing an artificial load thereon, and thus speeds up the warming process taking place within the engine upon starting thereof. The valve is moved by an actuating piston within a hydraulic cylinder using engine oil pressure controlled by an electrically operated valve receiving a pulse width modulated operating signal from the engine microcomputer, the operating signal being generated to provide a desired back pressure as a function of engine coolant temperature, engine speed, engine fuel comsumption, and actual back pressure. Operation of the system is enabled if the ambient air temperature is below 2.degree. C. and also for the period that the elapsed time since start of engine is less than thirty seconds, the latter enablement being provided to exercise the system during extended periods of warm weather operation when the system would otherwise be inactive.

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Des Plaines, IL, United States of America

Dale A Oehlerking