Failure determination system, failure determination method and engine control unit for variable-cylinder internal combustion engine

摘要

There is provided a failure determination system for a variable-cylinder internal combustion engine which is capable of promptly and accurately carrying out failure determination of the valve-actuating system for cylinders for being made idle during a partial-cylinder operation mode. The failure determination system is capable of switching a cylinder operation mode between an all-cylinder operation mode in which all the cylinders are operated, and a partial-cylinder operation mode in which part of the cylinders are made idle. The failure determination system includes an ECU which executes a failure-determining operation mode for causing a valve-actuating mechanism to resume actuation of intake valves and exhaust valves of the part of the cylinders in a state in which fuel supply to the part of the cylinders is stopped, when the cylinder operation mode is shifted from the partial-cylinder operation mode to the all-cylinder operation mode. The ECU determines whether or not the valve-actuating system including the valve-actuating mechanism has failed, based on an oxygen concentration detected when the failure-determining operation mode is executed.