Selective catalytic reduction system

A selective catalytic reduction system comprising:

• a selective catalytic reduction device provided in an exhaust pipe for an engine;
• a dosing valve that injects urea solution into exhaust gas in the exhaust pipe on an upstream side of the selective catalytic reduction device;
• an NOx sensor that detects an NOx concentration in the exhaust gas;
• an electric heater for raising a temperature of the NOx sensor to a sensor operating temperature;
• and
• a dosing control device configured to—
• prohibit energization of the heater at a time of a start of the engine,
• permit the energization of the heater when engine revolutions become equal to or higher than a preset energization permission threshold value,
• wherein the energization of the heater is permitted to continue for a period of time equal to or exceeding a preset stabilization wait time, and
• wherein the preset stabilization wait time is a time from when the engine revolutions become equal to or higher than the preset energization permission threshold value to when supply of power from an alternating current generator becomes stabilized, and
• prohibit the energization of the heater when the engine revolutions become equal to or fall below a preset energization prohibition threshold value that is larger than 0, and
• permit the energization of the heater to continue for a period of time equal to or exceeding a preset recovery wait time during operation of the engine,
• wherein the energization of the heater continues when the engine revolutions become equal to or fall below the preset energization prohibition threshold value and the engine revolutions rise and exceed the preset energization prohibition threshold value before the energization is permitted to continue for a period of time equal to or exceeding the preset recovery wait time during operation of the engine, and
• wherein the preset recovery wait time is a time from when the engine revolutions become equal to or fall below the energization prohibition threshold value to when supply of power from a battery becomes unstabilized.