Exhaust Gas Purification System for Working Machine

Abstract

Disclosed is an exhaust gas purification system for a working machine. The system is provided with a filter for capturing particulate matter contained in exhaust gas from an engine, a differential pressure sensor for detecting a differential pressure between an exhaust upstream side and an exhaust downstream side of the filter, and a controller having a regeneration determination unit for determining whether or not a time, at which forced regeneration is needed, has been reached. The controller includes one that has a variation determination unit for determining whether or not a state quantity relevant to an operation of the engine, for example, an engine speed has varied abruptly and that, when the state quantity is determined to have abruptly varied, performs processing to invalidate the determination by the regeneration determination unit during a predetermined time in which an effect of the state quantity is considered to diminish.

1 . An exhaust gas purification system for a working machine provided with working equipment, a main body with the working equipment attached thereto, and an engine arranged on the main body to drive the working equipment, said exhaust gas purification system being provided with a filter for capturing particulate matter, which is contained in exhaust gas from the engine, on an exhaust downstream side, a differential pressure sensor for detecting a differential pressure between an exhaust upstream side and the exhaust downstream side of the filter, and a controller having a regeneration determination unit for determining, by a comparison between the differential pressure detected at the differential pressure sensor and a determinative differential pressure as a threshold level for determination, whether or not a time, at which forced regeneration is needed to burn the particulate matter captured on the filter, has been reached, wherein:
 the controller comprises one that has a variation determination unit for determining whether or not a state quantity relevant to an operation of the engine has varied abruptly and that, when the state quantity is determined to have abruptly varied by the variation determination unit, performs processing to invalidate the determination by the regeneration determination unit during a predetermined time in which an effect of the state quantity is considered to diminish to a negligible extent.   
     
     
         2 . The exhaust gas purification system according to  claim 1 , wherein:
 the controller has a first computing unit for computing a flow rate of exhaust gas, and a second computing unit for computing the determinative differential pressure based on the flow rate of exhaust gas as computed at the first computing unit and a map preset in the controller and indicating correlations between flow rates of exhaust gas and determinative differential pressures.   
     
     
         3 . The exhaust gas purification system according to  claim 2 , wherein:
 the exhaust gas purification system is further provided with:   a fuel control unit for controlling an injection quantity of fuel to be fed to the engine,   an intake air volume sensor for detecting a volume of intake air to be fed to the engine and outputting a detection signal to the controller,   an intake air temperature sensor for detecting a temperature of intake air and outputting a detection signal to the controller, and   an exhaust gas temperature sensor for detecting a temperature of exhaust gas from the engine and outputting a detection signal to the controller;   the controller further comprises:   a fuel injection quantity instruction unit for outputting an instruction signal to instruct the injection quantity of fuel to the fuel control unit, and   an intake air weight computing unit for computing a weight of intake air based on a density of intake air, which is determined according to the temperature of intake air as detected at the intake air temperature sensor and a map preset in the controller and indicating correlations between intake air temperatures and intake air densities, and the volume of intake air as detected at the intake air volume sensor;   an exhaust gas weight computing unit for computing a weight of exhaust gas based on the weight of intake air as computed at the intake air weight computing unit and the injection quantity of fuel as instructed by the fuel injection quantity instruction unit; and   the first computing unit of the controller performs processing to compute a flow rate of exhaust gas based on a density of exhaust gas, which is determined according to the temperature of exhaust gas as detected at the exhaust gas temperature sensor and a map preset in the controller and indicating correlations between exhaust gas temperatures and exhaust gas densities, and the weight of exhaust gas as computed at the exhaust gas weight computing unit.   
     
     
         4 . The exhaust gas purification system according to  claim 3 , wherein:
 the exhaust gas purification system is further provided with:   an engine speed sensor for detecting a revolution speed of the engine and outputting a detection signal to the controller; and   the state quantity relevant to the operation of the engine is at least one of the revolution speed of the engine as detected at the engine speed sensor, the injection quantity of fuel as instructed by the fuel injection quantity instruction unit, the volume of intake air as detected at the intake air volume sensor, and the flow rate of exhaust gas as computed at the first computing unit of the controller.