Patent ID: 7457701

Claim:
An air quantity estimation apparatus for an internal combustion engine having an intake passage for introducing outside air into a cylinder and a turbocharger including a compressor disposed in the intake passage and compressing air within the intake passage, the air quantity estimation apparatus estimating a cylinder-interior air quantity which is a quantity of air having been introduced into the cylinder, and the air quantity estimation apparatus comprising: an air flowmeter disposed in the intake passage upstream of the compressor and converting a flow rate of air passing through the intake passage, the flow rate being an input quantity, to an electrical physical quantity being an output quantity, and outputting the electrical physical quantity; compressor-inflow-air-flow-rate estimation means including an inverse model which is a model inverse to a forward model of the air flowmeter, the forward model describing the relation between the input quantity and the output quantity of the air flowmeter, and is configured such that when an output quantity of the forward model is supplied to the inverse model as an input quantity, the inverse model outputs a corresponding input quantity of the forward model as an output quantity, wherein the compressor-inflow-air-flow-rate estimation means obtains the output quantity of the inverse model as a compressor-inflow-air flow rate which is a flow rate of air actually flowing into the compressor at a present time point by supplying the electrical physical quantity actually output from the air flowmeter to the inverse model as the input quantity of the inverse model; and cylinder-interior-air-quantity estimation means including an air model which describes, in accordance with physical laws, behavior of air within the intake passage downstream of the compressor by use of a compressor-outflow-air flow rate which is a flow rate of air flowing out of the compressor into the intake passage, wherein the cylinder-interior-air-quantity estimation means estimates the cylinder-interior air quantity by applying the obtained compressor-inflow-air flow rate at the present time point as the compressor-outflow-air flow rate at the present time point to the air model.