System and method for protecting a turbocharger in the event of a

Abstract

An engine control system for protecting a turbocharger of an internal combustion engine from an overspeed condition occurring as a result of a failure of the turbocharger wastegate device. In one embodiment of the invention, sensors provide signals for engine speed, ambient pressure and boost pressure between the turbocharger and the engine intake. Correction factors are added to the boost pressure and ambient pressure signals, and a turbocharger pressure ratio is calculated from these signals. A reduced fueling table maps turbocharger pressure ratio and engine speed to reduced fueling signal values. An engine control computer utilizes a nominal fueling table that maps engine speed and boost pressure to nominal fueling signal values. The control computer also includes a decision module that selects the lesser of the nominal fueling signal values and the reduced fueling signal values and provides the selected value to the engine fueling system. In the event of a wastegate failure, the turbocharger wheelspeed will increase, followed by an increase in boost pressure. However, not all boost pressure increases are detrimental to the turbocharger (i.e., lead to excessive speed), so the present invention evaluates the turbocharger pressure ratio to determine when an excessive speed condition exists. If such a condition exists, the engine control computer selects the lesser fueling signal value from the reduced fueling table to decrease fueling to the engine, and ultimately to decrease the engine speed and load. The decreased engine speed and load reduces the exhaust gas mass flow rate, which reduces the turbocharger rotational speed to an acceptable level.