Trapped soot estimator

A diesel engine comprising:

• an exhaust system comprising a diesel particulate filter for trapping soot passing through the exhaust system as the engine operates;
• a trapped soot estimator for estimating soot trapped in the diesel particular filter comprising a processor for repeatedly executing an algorithm that calculates a data value for total soot trapped in the diesel particulate filter as the engine operates, wherein the algorithm is structured:
• a) to process data values for current engine speed and current engine torque for selecting from a steady-state soot estimation table containing data values of steady-state soot correlated with data values for engine speed and engine torque, a current data value for steady-state soot entering the diesel particulate filter, and for selecting from a transient soot estimation table containing data values of transient soot correlated with data values for engine speed and engine torque, a current data value for transient soot entering the diesel particulate filter;
• b) to calculate a current data value for a feed-forward instantaneous soot estimate by weighting the current data values for steady-state and transient soot as a function of changing engine operation, summing the weighted data values and subtracting a current data value for trapped soot being burned off by natural regeneration;
• c) and to repeatedly update a data value for a total soot estimate of soot trapped in the diesel particulate filter by adding to an existing data value for the total soot estimate the result of integrating a current data value for feed-forward instantaneous soot over a length of time since the prior update while also correcting the data value for total soot estimate by calculating a current data value for soot error between the current total soot estimate and a data value for trapped soot based on current exhaust flow and current differential pressure across the diesel particulate filter and processing the current data value for soot error by Kalman filter processing whose gain is controlled by at least one parameter related to engine operation.