A control unit prevents overheating of a particulate filter in an exhaust path of an internal combustion engine during regeneration of the particulate filter if the regeneration deviates from prescribed conditions. Overheating is prevented using one of two engine operations: a first operation with a relatively lower exhaust temperature and relatively higher oxygen surplus (lean operation), or a second operation with a relatively higher exhaust temperature and a relatively lower oxygen surplus (rich operation). Based on the filter temperature and amount of particulate sediment, a heating value in the particulate filter (the heat quantity of an oxidation reaction of burning particulates in the particulate filter) is calculated for each operation. The operation with a lower heat budget, i.e., the difference between the heating value and heat released, is selected to cool the filter.