Electronic control system for an engine and the method thereof

Claim 1

An electronic control system for an engine having, an intake manifold connected to said engine for inducing air and fuel mixture, an airflow meter mounted on said intake manifold via a throttle valve for measuring an amount of air induced thereof and for generating an air amount signal, an exhaust manifold connected to said engine for exhausting burnt gases, a nitrogen oxide concentration sensor inserted in said exhaust manifold for detecting a nitrogen oxide amount in said burnt gases and for producing a nitrogen oxide signal, a crank angle sensor mounted on said engine for sensing an engine speed and for generating an engine speed signal, a pressure sensor mounted on said engine for detecting a combustion pressure in a cylinder and for outputting a pressure signal, an EGR valve communicated to said exhaust manifold for recirculating exhaust gases to said intake manifold and mode setting means for switching an engine operating mode from an economy mode to a power mode or vise versa, the system comprising: driving condition determining means, responsive to said engine speed and pressure signals, for deciding an operating condition of said engine and for generating an operating condition signal; combustion fluctuating rate calculating means, responsive to said pressure signal, for calculating an actual combustion fluctuating rate and for generating a fluctuating rate signal; combustion fluctuating rate comparing means, responsive to said operating condition and said fluctuating rate signals, for deriving an optimum air-fuel ratio by comparing said fluctuating rate signal with a standard value stored in a map and for producing a first control signal; nitrogen oxide gas calculating means, responsive to said nitrogen oxide signal, for calculating an actual nitrogen oxide gas amount and for generating a nitrogen oxide signal; exhaust gas comparing means, responsive to said operating condition signal and said nitrogen oxide exhaust signals, for judging said optimum air-fuel ratio by comparing said actual nitrogen oxide gas amount with a desired nitrogen oxide value stored in a memory and for producing a second control signal; and emission gas recirculation rate setting means, responsive to said first and second control signals, for deciding an optimum EGR rate by referring a target EGR rate corresponded to each engine operating condition stored in an EGR map so as to accurately operate said EGR valve in both said economy and power modes.