Exhaust purification device of engine

An exhaust purification device of an engine comprising:

• an exhaust passage through which an exhaust gas discharged from an engine body flows;
• a urea injector which supplies urea water into the exhaust passage;
• a urea tank for storing the urea water;
• a supply pipe connecting the urea injector and the urea tank to each other;
• a pressurizing pump incorporated in the supply pipe, the pressurizing pump capable of supplying the urea water stored in the urea tank to the urea injector by generating a predetermined pressurizing force, and capable of performing a recovery operation of recovering the urea water supplied to the urea injector to the urea tank when the pressurizing force is stopped;
• an SCR catalyst which is disposed in the exhaust passage downstream of the urea injector and purifies NOx in the exhaust gas by a reduction action of ammonium generated from urea;
• and
• a controller for controlling an operation of the urea injector and an operation of the pressurizing pump, wherein
• the controller is configured to control the pressurizing pump such that the supply of the urea water to the urea injector is stopped, and the controller is configured to control the pressurizing pump to perform the recovery operation for recovering the urea water supplied to the urea injector to the urea tank in a case where an amount of ammonium adsorbed by the SCR catalyst is larger than a target adsorption amount, which is set such that the amount of ammonium adsorbed by the SCR catalyst becomes smaller as a temperature of the SCR catalyst is higher, under a condition where an internal temperature of the urea injector reaches a predetermined high temperature immediately before the urea water is boiled, and
• the target adsorption amount is preset based on an amount of ammonium adsorbable by the SCR catalyst, and the controller is configured to control the operation of the urea injector and the operation of the pressurizing pump such that the amount of ammonium adsorbed by the SCR catalyst becomes the target adsorption amount.

An exhaust purification method using an exhaust purification device of an engine which includes:

• an exhaust passage through which an exhaust gas discharged from an engine body flows;
• a urea injector which supplies urea water into the exhaust passage;
• a pump device which supplies urea water stored in a urea tank to the urea injector, the pump device capable of performing a recovery operation of recovering the urea water supplied to the urea injector to the urea tank;
• and
• an SCR catalyst which is disposed in the exhaust passage downstream of the urea injector and purifies NOx in the exhaust gas by a reduction action of ammonium produced from urea, the method comprising the steps of:
• determining whether or not an amount of ammonium adsorbed by the SCR catalyst is larger than a predetermined reference adsorption amount under a condition where an internal temperature of the urea injector reaches a predetermined high temperature, wherein the predetermined reference adsorption amount is a target adsorption amount preset based on an amount of ammonium adsorbable by the SCR catalyst;
• causing the pump device to stop the supply of the urea water to the urea injector and perform the recovery operation for recovering the urea water supplied to the urea injector to the urea tank in a case where the amount of ammonium adsorbed by the SCR catalyst is larger than the target adsorption amount under the condition where the internal temperature of the urea injector reaches the predetermined high temperature;
• and
• controlling an operation of the urea injector and an operation of the pump device such that the amount of ammonium adsorbed by the SCR catalyst becomes the target adsorption amount.