Conventionally, a diesel particulate filter is well known which collects and oxidizes particle matters included in exhaust gas of a diesel engine so as to enable so-called continuous regeneration. An art of so-called forced regeneration is also well known in which the particle matters collected in the diesel particulate filter are oxidized forcedly by using an intake throttle controlling an intake air amount, a common rail system enabling one or a plurality times of fuel injection or the like.
However, the switching between the continuous regeneration mainly performed in a high output driving range in which the temperature of exhaust gas is high and the forced regeneration mainly performed in a low output driving range in which the temperature of exhaust gas is low is performed automatically corresponding to the driving state of the diesel engine and the accumulated amount of particle matters in the diesel particulate filter (for example, see the Patent Literature 1), whereby an operator may recognize sudden engine noise or change of output characteristics as abnormality.
Though there is a demand of reduction of fuel consumption of the diesel engine for improving the fuel economical efficiency, there is a problem in that the control for reducing the fuel consumption increases the noise of the diesel engine. On the other hand, though there is a demand of reduction of noise of the diesel engine for improving the silence, there is a problem in that the control for reducing the noise increases the fuel consumption amount of the diesel engine.
Patent Literature 1: the Japanese Patent Laid Open Gazette 2005-282545