Patent ID: 8388712

Claim:
A method of operating a particulate matter retaining system coupled to an engine exhaust and an engine intake, the particulate matter retaining system comprising at least a first and a second filter, the method comprising: during a first condition, operating in a first mode with the first filter storing particulate matter and the second filter releasing stored particulate matter into the engine intake, with exhaust gas flowing in a first direction through the filters, where flowing in the first direction comprises flowing through the first filter before flowing through the second filter, and where during the first mode, at least some tailpipe gas is drawn from between the first and second filters for expulsion to the atmosphere; and operating in a second mode with the first filter releasing stored particulate matter into the engine intake and the second filter storing particulate matter, the exhaust gas flowing in a second, opposite, direction through the filters, where flowing in the second direction comprises flowing through the second filter before flowing through the first filter, and where during the second mode, at least some tailpipe gas is drawn from between the first and second filters for expulsion to the atmosphere.