CLOSED LOOP EXHAUST GAS RECIRCULATION CONTROL SYSTEM

摘要

CLOSED LOOP EXHAUST GAS RECIRCULATION CONTROL SYSTEM A closed loop exhaust gas recirculation (EGR) control system for an internal combustion engine having an intake system, an exhaust system, a throttle disposed within the intake system for controlling air flow therein, a conduit coupling the exhaust system to the intake system for supplying exhaust gas back to the intake system for controlling the generation and emission of oxides of nitrogen and for improving drivability and avoiding engine roughness. The EGR control system of the present invention includes a first memory preprogrammed with a look-up table of optimal EGR values indicative of EGR valve position or the like determined as a function of engine speed and throttle position and a second memory pre-programmed with the look-up table of optimal EGR values determined as a function of engine speed and absolute manifold pressure The actual operating parameters of engine speed, throttle position and absolute manifold pressure are accurately sensed and stored as multi-bit binary numbers or words indicative thereof. The most significant bits (MSB) of the words are used to address the first and second memory while the least significant bits(LSB) of the words are used to perform a double linear interpolation of the accessed values to compute accurate first and second EGR values. The second EGR value is substracted from the first EGR value to determine a difference indicative of the current EGR valve error. A previously computed and stored EGR error value used to determine the last valve position adjustment is then substracted from the current EGR error value to determine the total change in error value required to correct the EGR valve position at the next adjustment. A fractional portion of the total change in EGR error value is then applied to the previously stored EGR error value to update same so as to avoid rapid or abrupt adjustments in the valve position so as to avoid engine roughness etc. The updated EGR error value is converted into a control signal which is used to adjust the position of the EGR valve at the next scheduled valve adjustment time so as to regulate EGR flow as desired.