Abstract: An exhaust purification system that includes a selective catalytic reduction to purify NOx contained in an exhaust gas by using ammonia produced from urea water and an NOx sensor to acquire a value of the NOx contained in the exhaust gas, and the exhaust purification system includes: a reach time measurement unit that measures a reach time of the NOx value acquired by the NOx sensor, the reach time being a required time for the NOx value to reach, from a first predetermined determinative NOx value, a second predetermined determinative NOx value, which is higher than the first determinative NOx value; and a determination unit that determines that malfunction occurs in the NOx sensor when the reach time measured by the reach time measurement unit is equal to or shorter than a first predetermined determinative time.

Abstract: An exhaust purification system that includes a selective catalytic reduction to purify NOx contained in an exhaust gas by using ammonia produced from urea water and an NOx sensor to acquire a value of the NOx contained in the exhaust gas, and the exhaust purification system includes: a reach time measurement unit that measures a reach time of the NOx value acquired by the NOx sensor, the reach time being a required time for the NOx value to reach, from a first predetermined determinative NOx value, a second predetermined determinative NOx value, which is higher than the first determinative NOx value; and a determination unit that determines that malfunction occurs in the NOx sensor when the reach time measured by the reach time measurement unit is equal to or shorter than a first predetermined determinative time.

Abstract: A selective catalytic reduction system (SCR) that reduces a burden on a battery resulting from energization of a heater and a decrease in time during which an NOx concentration cannot be detected. The SCR system includes: an SCR device; a dosing valve; NOx sensors; an urea solution injection control unit; electric heaters for raising respective temperatures of the NOx sensors to a sensor operating temperature; and an energization permission unit that prohibits energization of the heaters at the time of a start of an engine and permits energization of the heaters when engine revolutions become equal to or exceed a preset energization permission threshold value and such state lasts for a period of time equal to or exceeding a preset stabilization wait time.

Abstract: A selective catalytic reduction system (SCR) that reduces a burden on a battery resulting from energization of a heater and a decrease in time during which an NOx concentration cannot be detected. The SCR system includes: an SCR device; a dosing valve; NOx sensors; an urea solution injection control unit; electric heaters for raising respective temperatures of the NOx sensors to a sensor operating temperature; and an energization permission unit that prohibits energization of the heaters at the time of a start of an engine and permits energization of the heaters when engine revolutions become equal to or exceed a preset energization permission threshold value and such state lasts for a period of time equal to or exceeding a preset stabilization wait time.