Patent ID: 6325041
Filing Date: 2001-12-04
Classification: F01N,F02B,F02D,Y02T

Abstract:
A control apparatus for a spark ignition type direct injection engine, which comprises:a fuel injection valve for directly injecting and supplying fuel into a combustion chamber in each cylinder of an engine; anda NOx adsorbing catalyst which is inserted in an exhaust path communicating with the combustion chamber, adsorbs NOx in an excess oxygen atmosphere with high oxygen concentration in exhaust gas, and releases the adsorbed NOx when the oxygen concentration decreases, andwhich controls an air-fuel ratio of the combustion chamber to stay lean with excessive air ratio .lambda..gtoreq.1.3 when the engine falls to a low-load range after the NOx adsorbing catalyst has been warmed up, comprising:exhaust gas recirculation means for recirculating some portion of exhaust gas from the exhaust path to an intake system of the engine;determination means for determining if a NOx release timing from the NOx adsorbing catalyst is reached;air-fuel ratio control means for controlling the air-fuel ratio of the combustion chamber to fall within a range 1<.lambda..ltoreq.1.1 when said determination means determines that the NOx release period has been reached;injection timing control means for controlling the fuel injection valve to divisionally inject fuel in two injections including leasing injection which falls within a range from an intake stroke to a former period of a compression stroke of the cylinder, and trailing injection which is set after a middle period of the compression stroke and before an ignition period, when said determination means determines that the NOx release period has been reached; andexhaust gas recirculation control means for controlling said exhaust gas recirculation means to recirculate a predetermined amount of exhaust gas, when said determination means determines that the NOx release period has been reached,wherein said exhaust gas recirculation control means controls said exhaust gas recirculation means to recirculate exhaust gas to the intake system to achieve a recirculation ratio of not less than 30%, and the recirculation ratio of exhaust gas is given by:(carbon dioxide concentration in intake path-carbon dioxide concentration in air)/(carbon dioxide concentration in exhaust path-carbon dioxide concentration in intake path).