Exhaust gas recirculation system

Method of controlling a stepper motor driven EGR valve to control the rate of exhaust gas recirculation in an internal combustion engine, comprising determining a desired EGR mass flow rate value that is equivalent to a desired EGR percent mass flow rate value as a function comprising a rotational speed value and an air-charge value of said engine, determining a pressure ratio value across an EGR orifice associated with said valve, and determining a required number of steps for said stepper motor as a function of said EGR mass flow rate value and said pressure ratio value under subsonic exhaust gas flow conditions and as function of said EGR mass flow rate value under sonic exhaust gas flow conditions to achieve the desired EGR percent mass flow rate value.

Method of controlling a stepper motor driven EGR valve to control the rate of exhaust gas recirculation in an internal combustion engine, comprising determining a desired EGR mass flow rate value that is equivalent to a desired EGR percent mass flow rate value as a function comprising a rotational speed value and an air-charge value of said engine, determining a pressure ratio value across an EGR orifice associated with said valve, determining a required number of steps for said stepper motor as a function of said EGR mass flow rate value and said pressure ratio value to achieve the desired EGR percent mass flow rate value, and limiting said EGR percent mass flow rate value as a function of manifold absolute pressure as it approaches a peak manifold absolute pressure value at a current engine speed, said function being expressed as

• pct.sub.-- load=MAP/[bp-FNxxg(am)*29.92/bp*sqrt((act+460)/560))]
• where pct.sub.-- load is percent of peak air flow, MAP is an absolute manifold pressure value, bp is a baormetric pressure value, FNxxg(am) is a pressure drop function across a throttle and air cleaner assembly at wide open throttle at standard barometric pressure, sqrt is a square root, act is an air charge temperature value on a fresh air side of an engine throttle plate.

EGR system for an internal combustion engine, comprising a stepper motor driven EGR valve to control the rate of exhaust gas recirculation in said engine and an electroniccontroller programmed to determine a desired EGR mass flow rate value that is equivalent to a desired EGR percent mass flow rate value as a function comprising a rotational speed value and an air-charge value of said engine, determining a pressure ratio value across an EGR orifice controlled by said EGR valve, and determining a required number of steps for said stepper motor as a function of said EGR mass flow rate value and said pressure ratio value to achieve the desired EGR percent mass flow rate value.

EGR system for an internal combustion engine, comprising a stepper motor driven EGR valve to control the rate of exhaust gas recirculation in said engine and an electronic controller programmed to determine a desired EGR mass flow rate value that is equivalent to a desired EGR percent mass flow rate value as a function comprising a rotational speed value and an air-charge value of said engine, determining a pressure ratio value across an EGR orifice associated with said valve, and determining a required number of steps for said stepper motor as a function of said EGR mass flow rate value and said pressure ratio value under subsonic exhaust gas flow conditions and as function of said EGR mass flow rate value under sonic exhaust gas flow conditions to achieve the desired EGR percent mass flow rate value.

Method of estimating air-charge temperature to an intake manifold of an internal combustion engine having an exhaust gas recirculation system with an EGR valve, comprising:

• a) determining a manifold charge temperature value using a temperature sensor in said intake manifold,
• b) determining an ambient air temperature value using a temperature sensor located external of an air cleaner assembly of said engine,
• c) estimating said air-charge temperature from at least one of the ambient air temperature value and the manifold charge temperature value depending on position of said EGR valve.

EGR system having an EGR valve for an internal combustion engine, comprising

• a) a temperature sensor in an intake manifold of said engine for determining a manifold charge temperature value,
• b) a temperature sensor located external of an air cleaner assembly of said engine for determining an ambient air temperature value,
• c) an electronic controller programmed to estimate an air-charge temperature from at least one of the ambient air temperature value and the manifold charge temperature value depending on position of said EGR valve.