System and method for determining set point location for oxidant-based engine air/fuel control strategy

#The present invention relates generally to adjusting the air/fuel ratio in the cylinders of an internal combustion engine to control automotive emissions. More particularly, the present invention relates to a method and system for determining an oxidant set point location inside of a catalytic converter that is used in connection with a system that adjusts the air/fuel ratio in the cylinders based on the amount of oxidants stored in the catalytic converter.

#To minimize the amount of emissions exhausted into the atmosphere, modern automotive vehicles generally include one or more catalytic converters, or emission control devices, in the exhaust system of the vehicle. These emission control devices store oxygen and NOx (collectively, oxidants) from the vehicle exhaust stream when the engine is operated with a relatively lean air/fuel ratio. On the other hand, when the engine is operated with a relatively rich air/fuel ratio, they release the stored oxygen and NOx, which then react with the HC and CO produced by the engine. In this way, the emission of both NOx and hydrocarbons (HC and CO) into the atmosphere is minimized.

#The inventors have recognized a disadvantage with conventional air-fuel ratio control systems. In particular, the inventors have recognized that these systems attempt to maintain the engine at stoichiometry (or another desired air-fuel ratio). However, this has the disadvantage that engine air-fuel control is decoupled from the state of oxidant storage of the emission control device. The convention system relies on air-fuel feedback to compensate for this oversight.

#FIG. 1 is an illustrative block diagram of an internal combustion engine, according to a preferred embodiment of the invention.

#FIG. 2 is a schematic diagram illustrating the major functions of a preferred embodiment of the invented system and method.

#FIG. 3 is a flowchart that illustrates a preferred embodiment of the available oxidant storage estimator algorithm of the present invention.

#FIG. 1 illustrates an exemplary internal combustion engine according to a preferred embodiment of the invention. Fuel delivery system 11 of a conventional automotive internal combustion engine 13 is controlled by controller 15, such as an EEC or PCM. Engine 13 comprises fuel injectors 18, which are in fluid communication with fuel rail 22 to inject fuel into the cylinders (not shown) of engine 13, and temperature sensor 132 for sensing temperature of engine 13. Fuel delivery system 11 has fuel rail 22, fuel rail pressure sensor 33 connected to fuel rail 22, fuel line 40 coupled to fuel rail 22 via coupling 41, fuel delivery system 42, which is housed within fuel tank 44, to selectively deliver fuel to fuel rail 22 via fuel line 40.

#Engine 13 also comprises exhaust manifold 48 coupled to exhaust ports of the engine (not shown). Catalytic converter 52 is coupled to exhaust manifold 48. In the preferred embodiment, catalytic converter 52 is a multiple brick catalyst. FIG. 9 illustrates an exemplary multiple brick catalyst having three bricks, 52A, 52B, and 52C. Oxygen sensors 902, 904, and 906, preferably being EGO, UEGO or HEGO sensors, are positioned respectively behind bricks 52A, 52B, and 52C. Referring again to FIG. 1, a first conventional exhaust gas oxygen (EGO) sensor 54 is positioned upstream of catalytic converter 52 in exhaust manifold 48. A second conventional exhaust gas oxygen (EGO) sensor 53 is positioned downstream of catalytic converter 52 in exhaust manifold 48. EGO sensors 53 and 54 may comprise other known oxygen or air/fuel ratio sensors, such as HEGO or UEGO sensors. Engine 13 further comprises intake manifold 56 coupled to throttle body 58 having throttle plate 60 therein. Intake manifold 56 is also coupled to vapor recovery system 70.

#Vapor recovery system 70 comprises charcoal canister 72 coupled to fuel tank 44 via fuel tank connection line 74. Vapor recovery system 70 also comprises vapor control valve 78 positioned in intake vapor line 76 between intake manifold 56 and charcoal canister 72.