Patent ID: 7950225

Claim:
An exhaust control system for an internal combustion engine provided with an exhaust gas processing device and a NOx purifying catalyst which are arranged in series in an exhaust system, comprising: a first temperature detector for detecting a temperature of the exhaust gas processing device; a second temperature detector for detecting a temperature of the NOx purifying catalyst; a control means for controlling an exhaust temperature to conduct a regeneration process for removing sulfur contents trapped by the NOx purifying catalyst; a control mode selection means for selecting one of a plurality of exhaust temperature control modes according to a relationship between an output from the first temperature detector and an output from the second temperature detector, wherein the control means conducts exhaust temperature control according to the control mode selected by the control mode selection means, wherein the plurality of control modes comprise a main injection control mode in that an exhaust air fuel ratio (exhaust A/F) is controlled by controlling an amount of main fuel injection during combustion, and a supplemental injection control mode for controlling the exhaust A/F by controlling an amount of supplemental fuel injection performed after the main fuel injection; and a judgment means for judging whether or not the output from the first temperature detector is above a first predetermined temperature and whether or not the output from the second temperature detector is above a second predetermined temperature, wherein when the output from the first temperature detector is found to be above the first predetermined temperature and/or when the output from the second temperature detector is found to be above the second predetermined temperature, the control mode selection means selects an exhaust temperature control mode that lowers the exhaust temperature, and wherein when the output from the first temperature detector is found to be above the first temperature or when the output from the second temperature detector is found to be above the second temperature during when the supplemental injection control mode is selected, the control means stops the supplemental injection, and when the output from the first temperature detector is found to be beyond a third predetermined temperature that is higher than the first predetermined temperature or when the output from the second temperature detector is found to be higher than a fourth predetermined temperature that is higher than the second predetermined temperature after the stopping of the supplemental injection, the control mode selection means selects the main injection control mode to make the exhaust A/F rich.