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A trap system has been developed that collects particulate using two small filters and regenerates alternately by electric heaters. This system contains a new idea in detection of the amount of particulate accumulation in the filters. The system counts the amount using a particulate accumulation rate map which is a function of the engine load and speed. In vehicle test with this trap system, the particulate collection efficiency and the regeneration efficiency were proved to be high enough for practical use. The test results also showed that the shutdown performance of the route switch valve greatly influenced the regeneration efficiency.

In response to stringent particulate matter (PM) emission regulations worldwide, developments of diesel particulate filter (DPF) continue apace in addition to engine modification for PM reduction. Particularly with buses used in urban areas, reduction methods in black smoke emissions are being researched in addition to the efforts to satisfy the aforementioned PM regulations. The system described in this paper was developed for use mainly with buses in large urban concentrations. The system described in this paper mainly consists of both wall-flow monolith filters for filtration of PM emissions and electric heaters for regeneration. A key feature of this system is that exhaust gas is used for effective combustion of PM during regeneration. With conventional systems, airpumps have been used to feed air for PM combustion during regeneration. With the new system, however, the use of an air pump was discontinued due to durability and cost considerations.