Mass air flow meter

Claim 1

A closed throttle air flow meter for an internal combustion engine having an intake manifold, an induction passage opening from the atmosphere to the intake manifold and including a throttle bore and a variable position throttle in the throttle bore for varying the effective area of the induction passage to regulate the air flow into the intake manifold and further including a throttle bypass passage opening from the atmosphere to the intake manifold and including a variable position valve for varying the effective area of the bypass passage to regulate the air flow into the intake manifold bypassing the throttle, the air flow meter comprising, in combination: means for controlling the position of the valve in the bypass passage to control the engine idle speed to a predetermined value during an idle speed operating mode of the engine, the total air flow into the intake manifold at the desired engine idle speed having a predetermined value so that the air flow through the throttle bore is equal to the predetermined value less the air flow through the bypass passage; means for storing the position of the variable position valve when the engine is at the predetermined idle speed value during the engine idle speed operating mode, the stored value representing the air flow value through the bypass passage and therefore the flow value and effective area of the induction passage opening defined by the closed throttle; means for storing a schedule of values of the effective area A 1 of the induction passage opening defined by the closed throttle as a function of the position of the variable position valve when the engine is at the predetermined idle speed; means for storing a schedule of values of the effective area A 2 of the bypass passage defined by the position of the variable position valve; means for measuring the value P 0 of the barometric pressure; means for measuring the value P 1 of the intake manifold; means for measuring the value T of the manifold air temperature; means responsive to the scheduled values of A 1 and A 2 corresponding to the stored position of the variable position valve and the present value of the variable position valve, respectively, and the values P 0 of the barometric pressure, P 1 of the intake manifold and T of the manifold air temperature for determining the total air flow into the engine during closed throttle position in accord with the expression AIR FLOW =(A 1 +A 2 ) F(P 0 ) F(P 1 /P 0 ) F(T) where F(P 0 ), F(P 1 /P 0 ) and F(T) are predetermined functions of the pressure P O , the pressure ratio P 1 /P 0 and the temperature T.