Abstract: An exhaust gas recirculation control system such that the throttle valve is controlled by two vacuum actuators through three stages of fully-opened, half-opened, and fully closed positions, in addition to the control of the exhaust gas recirculation control valve, in accordance with the engine operating conditions including engine load. The EGR valve is fully closed under a heavy engine load and fully opened under a medium and light engine load, and the throttle valve is fully opened under a heavy engine load, half opened under a medium engine load, and fully closed under a light engine load, under due consideration of engine speed.

Abstract: An EGR control system for a diesel engine, comprises an EGR passageway connecting an intake passageway and an exhaust passageway to recirculate engine exhaust gas back to the engine, an EGR control valve operatively disposed in the EGR passageway to control the flow of the recirculated exhaust gas passing through the EGR passageway, a detecting device for detecting at least one of engine speed, engine load and engine coolant temperature to produce at least a signal dependent thereon, and a control device for controlling the operation of the EGR control valve in response to the signal from the detecting device, thereby controlling the amount of the recirculated exhaust gas in accordance with engine operating conditions.

Abstract: In a diesel engine having a turbocharger for feeding supercharged air to the engine, an exhaust gas recirculation passage communicates between the exhaust passage from the engine and the intake passage to a compressor of the turbocharger. A first control valve closes the exhaust gas recirculation passage when the output pressure of the air leading from the compressor is lower than a first predetermined value or higher than a second predetermined value which is higher than the first predetermined value. A second control valve may be further provided within the exhaust gas recirculation passage so as to close the exhaust gas recirculation passage when the load applied to the engine is above a predetermined value.