Catalyst deterioration diagnosis device

A catalyst deterioration diagnosis device (10) for an engine-including device (1) including:

• an engine (21) having a combustion chamber (22) that exhausts exhaust gas;
• a catalyst (12) which is configured to purify the exhaust gas from the combustion chamber (22) of the engine (21);
• an upstream oxygen concentration sensor (13) provided upstream of the catalyst (12) in a flow direction of the exhaust gas, and configured to output a signal that varies in value depending on whether an air-fuel ratio of an air-fuel mixture is rich or lean and that does not gradually vary when the air-fuel ratio of the air-fuel mixture gradually varies;
• and
• a downstream oxygen concentration sensor (14) provided downstream of the catalyst (12) in the flow direction of the exhaust gas,
• the catalyst deterioration diagnosis device (10) being configured to diagnose a state of deterioration of the catalyst (12) in accordance with an output signal of the downstream oxygen concentration sensor (14) when the engine (21) is driven so that reversal between increasing and decreasing of a fuel amount supplied to the engine (21) is performed based on reversal of a rich/lean state of an output signal of the upstream oxygen concentration sensor (13), the catalyst deterioration diagnosis device comprising:
• a processor (31);
• and
• a non-transitory storage medium (32) having program instructions stored thereon, when, because a cycle of reversal of the rich/lean state of the output signal of the upstream oxygen concentration sensor (13) is disturbed such that the rich/lean state of the output signal of the upstream oxygen concentration sensor (13) is reversed three or more times in a period that is identical in length with a period in which the rich/lean state of the output signal of the upstream oxygen concentration sensor (13) is reversed twice when the cycle of reversal of the rich/lean state of the output signal of the upstream oxygen concentration sensor (13) is normal, a cycle of reversal between increasing and decreasing of the fuel amount is disturbed such that an increasing/decreasing of the fuel amount is reversed three or more times in a period that is identical in length with a period in which the increasing/decreasing of the fuel amount is reversed twice when the reversal between increasing and decreasing of the fuel amount is normal,
• the processor (31) being configured to execute at least a diagnosis process of diagnosing the deterioration state of the catalyst (12) based on plural sets of data of the output signal of the downstream oxygen concentration sensor (14) obtained in each unit period during a diagnosis period, the diagnosis period being a duration in which the rich/lean state of the output signal of the upstream oxygen concentration sensor (13) is reversed at least twice when the cycle of reversal of the rich/lean state of the output signal of the upstream oxygen concentration sensor (13) is normal, the diagnosis period having a length with which one driving cycle includes plural diagnosis periods, the sets of data obtained in each unit period during the diagnosis period being not susceptible to an influence of variations including both increase and decrease of the output signal of the downstream oxygen concentration sensor (14), and the output signal of the downstream oxygen concentration sensor (14) being influenced by disturbance of the reversal between increasing and decreasing of the fuel amount.