Failure determination system and method for internal combustion engine and engine control unit

A failure determination system for an internal combustion engine including a variable valve mechanism for inactivating a valve system associated with at least one of cylinders during a predetermined operation of the engine,

• the failure determination system comprising:
• a cylinder-discriminating module for discriminating a particular one of the cylinders;
• fuel injection valves for injecting fuel for the cylinders, on a cylinder-by-cylinder basis;
• an oxygen concentration-detecting module for detecting concentration of oxygen contained in exhaust gases exhausted from the engine;
• a misfire-detecting module for detecting a misfire condition of the engine, on a cylinder-by-cylinder basis;
• a fuel injection-stopping module for stopping fuel injection from said fuel injection valves to a cylinder of which occurrence of a misfire is detected by said misfire-detecting module;
• and
• a failure-determining module for determining that a failure of the variable valve mechanism has occurred, when an oxygen concentration parameter determined based on results of the detection by said oxygen concentration-detecting module assumes a value which indicates a richer value of an actual air-fuel ratio of the exhaust gases than a predetermined reference value does, under a condition of the stoppage of fuel injection being carried out by said fuel injection-stopping module.

A method of determining a failure of a variable valve mechanism of an internal combustion engine, the variable valve mechanism inactivating a valve system associated with at least one of cylinders during a predetermined operation of the engine,

• the method comprising the steps of:
• discriminating a particular one of the cylinders;
• injecting fuel for the cylinders, on a cylinder-by-cylinder basis;
• detecting concentration of oxygen contained in exhaust gases exhausted from the engine;
• detecting a misfire condition of the engine, on a cylinder-by-cylinder basis;
• stopping fuel injection from said fuel injection valves to a cylinder of which occurrence of a misfire is detected;
• and
• determining that a failure of the variable valve mechanism has occurred, when an oxygen concentration parameter determined based on results of the detection of oxygen concentration assumes a value which indicates a richer value of an actual air-fuel ratio of the exhaust gases than a predetermined reference value does, under a condition of the stoppage of fuel injection being carried out.