A controller restricts an operation amount of the variable valve actuation mechanism
of a fluid pressure operated type such that increase in the valve overlap amount
of an engine is restrained when the engine is in a transient operation state in
which the output of the engine increases. When the controller determines that the
variable valve actuation mechanism is in the locked state, the controller relaxes
the restriction imposed on the operation amount of the variable valve actuation
mechanism. Hence, a decrease in follow-up performance of valve properties to desired
properties is restrained while restraining temporary stagnation of increase in
engine rotational speed caused by vehicle acceleration.
