Patent ID: 8201396

Claim:
An exhaust gas cleaning apparatus for cleaning exhaust gas from an internal combustion engine, the engine including at least one cylinder and combustion in the cylinder has a lean-burn mode and a rich-burn mode, in the lean-burn mode the air/fuel mixture in the cylinder being lean, in the rich-burn mode the air/fuel mixture in the cylinder being rich, the exhaust gas cleaning apparatus comprising: a Lean NO x Trap (LNT) provided in an exhaust passage of the engine through which the exhaust gas flows, the LNT being configured to absorb NO x contained in the exhaust gas when the exhaust gas is lean and reduce the absorbed NO x when the exhaust gas turns to rich; and an electronic control unit configured, with executable programmed logic, to perform: a combustion mode shift to shift the combustion in the cylinder from the lean-burn mode to the rich-burn mode, thereby making the exhaust gas turn from lean to rich, the combustion mode shift comprising: a first estimation to estimate a torque-producing fuel quantity for a fuel injection which is made by a fuel injector into the cylinder when the combustion in the cylinder is in the lean-burn mode, the torque-producing fuel quantity representing the quantity of fuel which is injected into the cylinder through the fuel injection and burnt in the cylinder to produce torque of the engine; a second sing estimation to estimate an excess oxygen ratio for an upcoming fuel injection which is to be made by the fuel injector into the cylinder during a time period of shifting the combustion in the cylinder from the lean-burn mode to the rich-burn mode, the excess oxygen ratio being estimated based on a cylinder oxygen quantity, which represents the quantity of oxygen currently present in the cylinder, and a command injection quantity for a previous fuel injection made by the fuel injector; a third estimation to estimate a fuel burning percentage for the upcoming fuel injection based on the excess oxygen ratio estimated by the second estimation; set a command injection quantity for the upcoming fuel injection based on the torque-producing fuel quantity estimated by the first estimation and the fuel burning percentage estimated by the third estimation; and control the fuel injector to inject the command injection quantity, set by the setting unit, of the fuel into the cylinder in the upcoming fuel injection.