Exhaust after-treatment system for a motor vehicle

摘要

The system includes two exhaust gas treatment devices (14,26) and a parallel path, continuous flow, flow rate sensitive exhaust temperature modification circuit (16,18) for conducting exhaust gases from the first treatment device to the second treatment device. Preferred Features: The temperature modification circuit has a number of parallel flow paths, with at least one thermally insulated exhaust conduit (16) having a relatively lower restriction to flow at lower mass flow rates and a relatively greater restriction to flow at higher mass flow rates, and at least one exhaust conduit (18) without thermal insulation and having a relatively greater restriction to flow at lower mass flow rates and a relatively lower restriction to flow at higher mass flow rates. The circuit conserves a higher percentage of heat within the exhaust stream at lower mass flow rates, while rejecting a higher percentage of heat at a higher mass flow rate. The exhaust conduit conducts the exhaust gas through a heat exchanger so to increase the heat transfer to ambient. The heat exchanger has a laminar flow element (20) having a monolithic exhaust treatment substrate without an active wash coat.