Diagnostic apparatus for variable valve control system

An apparatus that diagnoses an abnormality of a variable valve lift control system having variable valve lift devices of a plurality of systems, the variable valve lift devices of the plurality of systems varying the valve lift characteristics of at least one of an intake valve and an exhaust valve of each cylinder in an internal combustion engine, the apparatus comprising:

• a cylinder-by-cylinder air-fuel ratio estimation means that estimates an air-fuel ratio of each cylinder;
• and
• an abnormality diagnosis means that diagnoses presence or absence of an abnormality in the variable valve lift devices on the basis of an air-fuel ratio estimate value of each cylinder and controlled states of the variable valve lift devices,
• wherein the air-fuel ratio estimate value of each cylinder is estimated by the cylinder-by-cylinder air-fuel ratio estimation means.

An apparatus that diagnoses an abnormality of an internal combustion engine having a plurality of intake air efficiency varying means for varying intake air efficiency, the apparatus comprising:

• an operating-state detection means that detects an operating state of the internal combustion engine;
• a first abnormality determination means that determines whether a state of intake air efficiency varying control, which is performed by the plurality of intake air efficiency varying means, is abnormal on the basis of an operating state detected by the operating-state detection means;
• and
• a second abnormality determination means that forcedly drives the plurality of intake air efficiency varying means one by one when the first abnormality determination means determines that a state of the intake air efficiency varying control is abnormal,
• wherein the second abnormality determination means determines the intake air efficiency varying means, which is abnormal, depending upon whether the operating state detected by the operating-state detection means changes corresponding to forced driving of the intake air efficiency varying means.

A method of diagnosing an abnormality of an internal combustion engine having a plurality of intake air efficiency varying mechanisms for varying intake air efficiency, the method comprising:

• detecting an operating state of the internal combustion engine;
• determining whether a state of intake air efficiency control, which is performed by the plurality of intake air efficiency varying mechanisms, is abnormal on the basis of the detected operating state;
• forcedly driving the plurality of intake air efficiency varying mechanisms one by one when a determination has been made that a state of the intake air efficiency varying control is abnormal;
• and
• determining which of the intake air efficiency varying mechanisms is abnormal, depending upon changes in the detected operating state in response to the forcedly driving of the intake air efficiency varying mechanisms.