Exhaust temperature raising apparatus and method for internal combustion engine

An exhaust temperature raising apparatus for an internal combustion engine, comprising:

• an exhaust passage connected to the internal combustion engine;
• an exhaust throttle valve that is provided in the exhaust passage and that adjusts an amount of flow of an exhaust gas flowing in the exhaust passage;
• valve control means for controlling the exhaust throttle valve to a substantially completely closed state at a time when an amount of an unburned fuel component contained in the exhaust gas is to be reduced;
• engine air-fuel ratio control means for operating the internal combustion engine at a theoretical air-fuel ratio or a fuel-excess air-fuel ratio when the exhaust throttle valve is controlled to the substantially completely closed state by the valve control means;
• and
• secondary air supply means for supplying a secondary air to an upstream portion of the exhaust passage when the exhaust throttle valve is controlled to the substantially completely closed state by the valve control means,
• wherein the time when the unburned fuel component contained in the exhaust gas is to be reduced is when the internal combustion engine is in a warm-up operation state following a cold start,
• wherein the internal combustion engine is a lean-burn direct-injection internal combustion engine that has fuel injection means for injecting a fuel directly into a cylinder and that is capable of switching between a stratified charge combustion operation and a homogeneous combustion operation, and
• wherein when the exhaust throttle valve is controlled to the substantially completely closed state by the valve control means, the engine air-fuel ratio control means causes the homogeneous combustion operation of the internal combustion engine and causes the fuel injection means to subsidiarily inject the fuel in addition to injection of a main amount of the fuel.