EXHAUST GAS RECIRCULATION CONTROL SYSTEM

A control system for controlling exhaust gas recirculation in an internal combustion engine. The output of a throttle position sensor is used as an input to two parallel filters. The first filter is a lag-lead compensated filter which functions as a differentiator, producing an output proportional to the instantaneous rate of change of the throttle position.. The second filter is a fixed-rate tracking filter which generates a tracking signal that tracks the input signal. The tracking signal, however, cannot vary by more than a maximum predetermined rate. The output of the second filter is the difference between the input signal and the tracking signal. The outputs of the two filters are summed and applied to a hysteretic comparator, which turns the EGR valve off when the sum exceeds an upper threshold and turns the EGR valve back on when the sum has decayed below a lower threshold. As a result, the first filter output is largely responsible for triggering the EGR valve to turn off, while the second filter output is largely responsible for determining how long the EGR valve remains off.