Exhaust gas purifying device for engine

An exhaust gas purifying device for an engine having an exhaust passage through which exhaust gas including excess oxygen flows, comprising:

• a catalyst arranged in the exhaust passage to purify the exhaust gas, the catalyst having an oxidizing ability;
• a feeding device that feeds a reducing agent to the catalyst to make the air-fuel ratio of the exhaust gas flowing into the catalyst rich when sulfate adsorbed in the catalyst is to be desorbed and reduced;
• a judging device that obtains an amount of sulfate adsorbed in the catalyst and judges whether the adsorbed sulfate amount is larger than a predetermined amount;
• and
• a controller that controls the feeding device to feed the reducing agent to the catalyst temporarily to desorb the adsorbed sulfate from the catalyst and to reduce the sulfate when the adsorbed sulfate amount is judged to be larger than the predetermined amount;
• wherein a degree of richness of the air-fuel ratio of the exhaust gas flowing into the catalyst when the sulfate adsorbed in the catalyst is to be desorbed and reduced, is controlled in accordance with an engine operating condition.

An exhaust gas purifying device for an engine having an exhaust passage through which exhaust gas including excess oxygen flows, comprising:

• a catalyst arranged in the exhaust passage to purify the exhaust gas, the catalyst having an oxidizing ability, the catalyst having an optimum temperature range for sulfate reduction;
• a feeding device that feeds a reducing agent to the catalyst;
• a judging device that obtains an amount of sulfate adsorbed in the catalyst and judges whether the adsorbed sulfate amount is larger than a predetermined amount;
• a controller that controls the feeding device to feed the reducing agent to the catalyst temporarily to desorb the adsorbed sulfate from the catalyst and to reduce the sulfate when the adsorbed sulfate amount is judged to be larger than the predetermined amount;
• and
• a determination device that determines whether the catalyst temperature is within the optimum temperature range for sulfate reduction, wherein the reducing agent is fed to the catalyst when the adsorbed sulfate amount is judged to be larger than the predetermined amount and the catalyst temperature is determined to be within the optimum temperature range for sulfate reduction, to desorb and reduce sulfate adsorbed in the catalyst.

An exhaust gas purifying device for an engine having an exhaust passage through which exhaust gas including excess oxygen flows, comprising:

• a catalyst arranged in the exhaust passage to purify the exhaust gas, the catalyst having an oxidizing ability;
• a feeding device that feeds a reducing agent to the catalyst;
• a judging device that obtains an amount of sulfate adsorbed in the catalyst and judges whether the adsorbed sulfate amount is larger than a predetermined amount;
• a controller that controls the feeding device to feed the reducing agent to the catalyst temporarily to desorb the adsorbed sulfate from the catalyst and to reduce the sulfate when the adsorbed sulfate amount is judged to be larger than the predetermined amount;
• and
• wherein the feeding device feeds the reducing agent to the catalyst continuously while sulfate reduction is stopped to reduce NOx in the catalyst.

An exhaust gas purifying device for an engine having an exhaust passage through which exhaust gas including excess oxygen flows, comprising:

• a catalyst arranged in the exhaust passage to purify the exhaust gas, the catalyst having an oxidizing ability;
• a feeding device that feeds a reducing agent to the catalyst;
• a judging device that obtains an amount of sulfate adsorbed in the catalyst and judges whether the adsorbed sulfate amount is larger than a predetermined amount;
• a controller that controls the feeding device to feed the reducing agent to the catalyst temporarily to desorb the adsorbed sulfate from the catalyst and to reduce the sulfate when the adsorbed sulfate amount is judged to be larger than the predetermined amount;
• and
• wherein a concentration of the reducing agent in the exhaust gas flowing into the catalyst is set to keep the concentration of the reducing agent in the exhaust gas discharged from the catalyst lower than an allowable value.

An exhaust gas purifying device for an engine having an exhaust passage through which exhaust gas including excess oxygen flows, comprising:

• a catalyst arranged in the exhaust passage to purify the exhaust gas, the catalyst having an oxidizing ability;
• a feeding device that feeds a reducing agent to the catalyst;
• a judging device that obtains an amount of sulfate adsorbed in the catalyst and judges whether the adsorbed sulfate amount is larger than a predetermined amount;
• a controller that controls the feeding device to feed the reducing agent to the catalyst temporarily to desorb the adsorbed sulfate from the catalyst and to reduce the sulfate when the adsorbed sulfate amount is judged to be larger than the predetermined amount;
• and
• wherein the reducing agent is fed to the catalyst intermittently when the sulfate adsorbed in the catalyst is to be desorbed and reduced.