Diesel engine exhaust gas recirculation control system

Claim 1

For a diesel engine for a vehicle, comprising an air intake passage, an exhaust passage, and an exhaust gas recirculation passage whose upstream end is communicated to an intermediate point of said exhaust passage and whose downstream end is communicated to an intermediate point of said air intake passage. an exhaust gas recirculation control system, comprising: (a) a fluid pressure operated exhaust gas recirculation control valve which controls the flow resistance of said exhaust gas recirculation passage according to a control fluid pressure supplied thereto so as to increase the flow resistance to a maximum substantially infinite valve as the control fluid pressure approaches atmospheric pressure; (b) an electrically operated switching over valve which, when actuated, changes over said control fluid pressure supplied to said exhaust gas recirculation control valve to atmospheric pressure; and (c) an exhaust gas recirculation control signal generating system, including a means for detecting engine load and jerk, which outputs a first fluid pressure control signal which is supplied to said exhaust gas recirculation control valve as said control fluid pressure so as to provide an appropriate amount of exhaust gas recirculation according to engine load, and a second electric control signal which actuates said switching over valve when the rate of change of engine load is greater than a certain predetermined value.