In order to meet increasingly strict PM legislation, diesel particulate filter systems (DPF) with a conversion rate of about 90% particulate matter (PM) are an essential after-treatment technology. Recently a filtering method using a catalyst has been proposed, which is called the “Continuously Regenerating DPF System[1],” and one can expect a significant degree of system simplification and cost reduction. In the previous report [2] basic characteristics about this continuously regenerating DPF were investigated. Results showed that in city mode driving, where exhaust temperatures are relatively low, continuous regeneration did not occur. Therefore, to “Continuously Regenerating DPF System,” active regeneration control system to oxidize and remove PM is necessary[3]. Then DPF system with higher reliability and active regeneration control method was proposed. This DPF system was fitted to a vehicle and tested at conditions typical of city traffic, when active regeneration is most needed.
In this report, the DPF system proposed in previous report was further developed and advanced with primary focus on driving condition was in need of active regeneration, those for which the average vehicle speed is very low. At the same time, a method to minimize fuel consumption in active regeneration was determined. First, the driving conditions of light-duty trucks actually drive in urban areas including cities and suburbs was carefully studied. Due to frequent and severe traffic congestion, it was understood that the average vehicle speed was very low (below about 12km/h) and as the average vehicle speed decreased, accelerator-off driving condition (idling and deceleration) increased, which consequently prevented the DPF from ever reaching the temperature required for active regeneration. Therefore, heat-up performance during accelerator-off driving condition improved, making active regeneration possible at average vehicle speeds below 12km/h. Next, optimization of the regeneration duration was investigated, leading to a method using the total oxygen passing through the filter during regeneration as a Judgment method of ending time of active regeneration. Compared to a method using a constant time, the fuel quantity required for active regeneration was reduced by about 20% in transient driving pattern.
These improvements led to development of a DPF system for commercial vehicles that is effective, efficient, and robust.