Patent ID: 7681442

Claim:
A throttle upstream pressure estimating apparatus for an internal combustion engine comprising: intake air pressure detecting means for detecting an intake air pressure Pm, which represents a pressure downstream of a throttle valve provided in an intake passage of the internal combustion engine; and throttle upstream pressure estimating means for repeatedly calculating a throttle upstream pressure, which represents a pressure upstream of the throttle valve, at a predetermined time intervals by using an equation of an intake system model which models behaviors of an intake air during a period where a change in the throttle upstream pressure and a change in a throttle opening degree cause a change in the intake air pressure Pm so as to cause a change in an actual cylinder charged air quantity, wherein the throttle upstream pressure estimating means substitutes a previous throttle upstream pressure Pthrup(i−1) for a part of a plurality of throttle upstream pressures included in the equation of the intake system model to calculate a present throttle upstream pressure Pthrup(i), and wherein the equation of the intake system model is represented by the following Equation: Gin = μ · A ⁢ Pthrup ⁡ ( i - 1 ) R · T · f ⁡ ( Pm ⁢ / ⁢ Pthrup ⁡ ( i ) ) Gin: throttled air quantity [kg/sec] μ: flow coefficient A: effective cross-sectional area of throttle opening [m 2 ] Pthrup(i−1): Previous throttle upstream pressure [Pa] Pthrup(i): Present throttle upstream pressure [Pa] Pm: intake air pressure [Pa] R: gas constant T: intake air temperature [K] f(Pm/Pthrup(i)): physical value determined based on Pm/Pthrup(i) A=πr 2 (1−cos 2 θ) r: radius of throttle valve [m] θ: throttle opening degree.