Device and method of determining deterioration of catalyst

1. A catalyst determining device comprising:

an oxidation catalyst disposed in an outlet passage in an engine, the oxidation catalyst comprising an adsorption substance for adsorbing and desorbing an exhaust component in exhaust and a catalytic substance capable of oxidizing the exhaust component;

a calculating unit for calculating a difference in oxygen concentration between upstream and downstream of the oxidation catalyst; and

a determination unit for determining deterioration of the oxidation catalyst through comparison of a plurality of the differences in oxygen concentration obtained at different temperatures of the oxidation catalyst by calculating unit.

2. The catalyst determining device according to claim 1 , wherein the determination unit determines the deterioration of the adsorption substance based on the plurality of differences in oxygen concentration at the different temperatures of the oxidation catalyst within a range equal to or lower than an oxidation initiation temperature at which oxidation of the exhaust component is initiated in the oxidation catalyst.

3. The catalyst determining device according to claim 2 , wherein the determination unit determines the deterioration of the adsorption substance through comparison of the difference in oxygen concentration obtained by the calculating unit at a temperature of the oxidation catalyst lower than a desorption initiation temperature at which the exhaust component initiates desorption from the adsorption component with the difference in oxygen concentration obtained by the calculating unit at another temperature of the oxidation catalyst within a range from the desorption initiation temperature to the oxidation initiation temperature.

4. The catalyst determining device according to claim 3 , wherein the determination unit determines the deterioration of the catalytic substance based on the difference in oxygen concentration at a temperature of the oxidation catalyst higher than the oxidation initiation temperature after the determination of deterioration of the adsorption substance, and distinguishes factors causing the deterioration of the oxidation catalyst based on the result of the determination of deterioration of the adsorption substance and the result of the determination of deterioration of the catalytic substance.

5. The catalyst determining device according to claim 1 , wherein the determination unit determines the deterioration of the oxidation catalyst if a difference between the plurality of differences in oxygen concentration is lower than a threshold.

6. The catalyst determining device according to claim 5 , wherein the determination unit comprises a provisional determination unit for provisionally determining possible deterioration of the oxidation catalyst if the difference in oxygen concentration obtained by the calculating unit is lower than a first prescribed value at a temperature of the oxidation catalyst lower than a desorption initiation temperature at which the exhaust component initiates desorption from the adsorption component.

7. The catalyst determining device according to claim 6 , wherein the determination unit changes the threshold for the difference between the plurality of differences in oxygen concentration with respect to the determination of deterioration of the oxidation catalyst in response to the result of the provisional determination by the provisional determination unit.

8. The catalyst determining device according to claim 7 , further comprising a temperature acquiring unit for acquiring the temperature of the oxidation catalyst, wherein the determination unit differentiates the states of the oxidation catalyst at different temperatures according to the temperature (T) acquired by the temperature acquiring unit.

9. A method of determining deterioration of an oxidation catalyst disposed in an outlet passage in an engine, the oxidation catalyst including an adsorption substance for adsorbing and desorbing an exhaust component in exhaust and a catalytic substance capable of oxidizing the exhaust component, the method comprising:

calculating a difference in oxygen concentration between upstream and downstream of the oxidation catalyst as a first difference in oxygen concentration if a temperature of the oxidation catalyst is a first temperature;

calculating a difference in oxygen concentration between upstream and downstream of the oxidation catalyst as a second difference in oxygen concentration if the temperature of the oxidation catalyst is a second temperature higher than the first temperature; and

performing the determination of deterioration of the oxidation catalyst by comparing the first difference in oxygen concentration with the second difference in oxygen concentration.