Importance

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Abstract

A method and apparatus for controlling the recirculation of exhaust gas in a diesel engine includes an EGR valve responsive to an EGR control signal for relatively opening and closing a recirculation duct to the passage of exhaust gas therethrough. A sensor provides a signal indicative of the level of particulates in the exhaust gas stream. Control circuitry responsive to various signals indicative of engine operating conditions, including the signal indicative of exhaust gas particulate level, provides an EGR control signal for regulating the EGR valve at least partly as a function of the sensed level of particulates in the exhaust gas stream. The engine operating condition signals typically are indicative of the speed of the engine or fuel injection pump, the engine load, and engine operating temperature. The particulate level signal is preferably provided by electrostatically sensing the passage of packets of charged particles by an electrically-passive, annular electrode positioned in or adjacent to the exhaust gas stream. The control circuitry includes storage of open loop EGR valve control signals as a function of speed and load, as well as particulate objective signals also as a function of speed and load. The sensed exhaust gas particulate level is compared with the appropriate particulate objective signal for the development of an error signal, which error signal is then used in an adaptive manner to adjust the open loop EGR control signal in a direction to diminish the particulate error signal. Such adaptive control of the EGR control signal as a function of the exhaust gas particulate level is further advantageous because a predeterminable relationship exists between exhaust particulate levels and NO.sub.x levels as a function of percent EGR. EGR control may be inhibited by depressed engine temperature.

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First Claim