An intake-air quantity estimation apparatus for an internal combustion
engine, including an intake-air quantity estimation device that includes
a cylinder pressure estimation device that estimates pressure within a
cylinder through calculation using a model of the cylinder obtained based
on a law of conservation of energy, the intake-air quantity estimation
device estimates a cylinder intake-air quantity based on the estimated
pressure within the cylinder, the cylinder intake-air quantity
representing the amount of air flowing into the cylinder.