Exhaust purification system and catalyst regeneration method

An exhaust purification system comprising:

• a NOx-occlusion-reduction-type catalyst that is provided in an exhaust passage of an internal combustion engine, occludes NOx in exhaust when the exhaust is in a lean state, and reduces and purifies the occluded NOx when the exhaust is in a rich state, and
• a control unit,
• wherein the control unit operates so as to execute the following processing:
• catalyst regeneration processing of reducing and purifying the NOx occluded in the NOx-occlusion-reduction-type catalyst by controlling at least one of an intake flow rate and a fuel injection amount to set the exhaust in the rich state, and
• inhibition processing of inhibiting performance of the catalyst regeneration processing when the internal combustion engine becomes a motoring state in which fuel injection is stopped, and inhibiting, when the internal combustion engine has started the fuel injection during the inhibition, performance of the catalyst regeneration processing from start of the fuel injection until a predetermined time period has elapsed, and
• wherein when an increase rate in a fuel injection amount of the internal combustion engine exceeds a predetermined upper limit threshold value, the control unit inhibits performance of the catalyst regeneration processing, and when the increase rate in the fuel injection amount of the internal combustion engine decreases to the upper limit threshold value or smaller during the inhibition, the control unit inhibits performance of the catalyst regeneration processing from when the increase rate in the fuel injection amount of the internal combustion engine has decreased to the upper limit threshold value or smaller until a predetermined time period has elapsed.

A catalyst regeneration method in an exhaust purification system including:

• an internal combustion engine;
• and a NOx-occlusion-reduction-type catalyst that is provided in an exhaust passage of the internal combustion engine, occludes NOx in exhaust when the exhaust is in a lean state and reduces, and purifies the occluded NOx when the exhaust is in a rich state, the method comprising:
• catalyst regeneration processing of reducing and purifying the NOx occluded in the NOx-occlusion-reduction-type catalyst by setting the exhaust in the rich state, and
• inhibition processing of inhibiting performance of the catalyst regeneration processing when the internal combustion engine becomes a motoring state in which fuel injection is stopped, and inhibiting, when the internal combustion engine has started the fuel injection during the inhibition, performance of the catalyst regeneration processing from start of the fuel injection until a predetermined time period has elapsed,
• wherein when an increase rate in a fuel injection amount of the internal combustion engine exceeds a predetermined upper limit threshold value, the inhibition processing inhibits performance of the catalyst regeneration processing, and when the increase rate in the fuel injection amount of the internal combustion engine decreases to the upper limit threshold value or smaller during the inhibition, the inhibition processing inhibits performance of the catalyst regeneration processing from when the increase rate in the fuel injection amount of the internal combustion engine has decreased to the upper limit threshold value or smaller until a predetermined time period has elapsed.