When controlling the valve characteristics of an intake valve and changing
the compression ratio, an upper variation limit compression ratio, which
is the upper limit of the variation of compression ratio, is determined
according to the actual valve characteristics of the intake valve
characteristics control. The upper variation limit compression ratio is
set to a valve at which the intake valve does not collide with the
piston. When a target compression ratio corresponding to the operation
state of the engine is larger than the upper variation limit compression
ratio, the compression ratio is set to the upper variation limit
compression ratio that is smaller than the target compression ratio.
Thus, collision between the intake valve and the piston can be prevented
while allowing the compression ratio to be increased up to the maximum
compression ratio of the range where the collision does not occur.