Reducing agent supply device and method for controlling reducing agent supply device

A control method of a reduction-causing agent supply device comprising:

• a tank configured to store a reduction-causing agent to be supplied into an exhaust pipe of an engine;
• a pumping unit comprising a pump configured to pump the reduction-causing agent stored in the tank;
• a reduction-causing agent supply passage configured to supply the pumped reduction-causing agent;
• an injection nozzle configured to inject the reduction-causing agent supplied through the reduction-causing agent supply passage into the exhaust pipe;
• a drawing-back unit comprising the pump and a switching valve and being configured to draw back the reduction-causing agent present inside the reduction-causing agent supply passage toward the tank,
• the control method comprising:
• after the engine is stopped,
• operating the drawing-back unit, while a valve of the injection nozzle is closed, to draw back the reduction-causing agent present inside the reduction-causing agent supply passage toward the tank;
• operating the drawing-back unit, while the valve of the injection nozzle is open, to introduce gas present inside the exhaust pipe into the injection nozzle and the reduction-causing agent supply passage;
• operating the pumping unit, while the valve of the injection nozzle is closed, to supply the reduction-causing agent into the reduction-causing agent supply passage to compress the gas introduced in the reduction-causing agent supply passage;
• opening the valve of the injection nozzle to discharge the compressed gas into the exhaust pipe through the injection nozzle, and
• closing the valve of the injection nozzle before the reduction-causing agent present inside the reduction-causing agent supply passage reaches the injection nozzle while the pump is kept in operation.

A reduction-causing agent supply device, comprising:

• a tank configured to store a reduction-causing agent to be supplied into an exhaust pipe of an engine;
• a pumping unit comprising a discharging pump configured to pump the reduction-causing agent stored in the tank;
• a reduction-causing agent supply passage configured to supply the pumped reduction-causing agent;
• an injection nozzle configured to inject the reduction-causing agent supplied through the reduction-causing agent supply passage into the exhaust pipe;
• a drawing-back unit comprising a drawing-back pump configured to draw back the reduction-causing agent present inside the reduction-causing agent supply passage toward the tank;
• and
• a controller configured to control an operation of each of the pumping unit, the injection nozzle and the drawing-back unit, wherein
• the controller is configured to perform a reduction-causing agent drawing-back process and a compressed gas discharge process, after the engine is stopped, wherein
• in the reduction-causing agent drawing-back process;
• the controller is configured to
• operate the drawing-back unit, while a valve of the injection nozzle is closed, to draw back the reduction-causing agent present inside the reduction-causing agent supply passage toward the tank;
• and
• operate the drawing-back unit, while the valve of the injection nozzle is open, to introduce gas present inside the exhaust pipe into the injection nozzle and the reduction-causing agent supply passage, and
• in the compressed gas discharge process;
• the controller is configured to
• operate the pumping unit, while the valve of the injection nozzle is closed, to supply the reduction-causing agent into the reduction-causing agent supply passage to compress the gas introduced in the reduction-causing agent supply passage;
• open the valve of the injection nozzle to discharge the compressed gas into the exhaust pipe through the injection nozzle;
• and
• close the valve of the injection nozzle before the reduction-causing agent present inside the reduction-causing agent supply passage reaches the injection nozzle while the discharging pump is kept in operation.