In this study, the various influences on backpressure based DPF monitoring have been investigated. A number of inputs are influenced by tolerances that negatively affect measured pressure, modelled volume flow and modelled backpressure. A simulation has been performed to evaluate the influence of those tolerances on the final diagnostic robustness. For some of the tolerances, state-of-the-art tolerance values have been defined. Based on the simulation, upper limits were defined for the remaining tolerances. In a series application, if the defined tolerances can be met, a robust monitoring of a DPF using just the pressure sensor appears to be possible. In this case, no other monitoring strategy, e.g. a PM sensor, is needed.The defined numbers are assumed for vehicles with engine-out soot emissions around 40 mg/km. If above defined tolerances cannot be reached, it is helpful to reduce engine- out soot emissions. The correlation is roughly linear, at least if changes are not too large: A 20 % increase in tolerances must be countered by a 20 % decrease of raw emissions.The simulation has been performed using average DPF characteristics. For vehicles with different characteristics, e.g. higher or lower backpressure, the relative impact of the individual tolerances may change.
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- System influence and requirements for monitoring diesel particulate filters without particulate matter sensors
Dr. Holger Pieta
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