Method for regenerating an NOx storage catalyst

A method of regenerating a NOx storage catalyst of the type arranged in an exhaust tract of an internal combustion engine operated with air excess, wherein a NOx measurement transducer is disposed downstream of the Nox storage catalyst in an exhaust gas flow direction, the method which comprises:

• during a regeneration phase, briefly operating the internal combustion engine with a rich air/fuel mixture to produce a reducing agent and converting NOx stored in the Nox storage catalyst with the addition of the reducing agent;
• providing an amperometric NOx measurement transducer formed with a solid-state electrolyte and having a first measuring cell, a second measuring cell, a reference electrode exposed to ambient air, a first electrode, a second electrode, and an outer electrode;
• measuring an oxygen concentration in the first measuring cell via a first Nernst voltage between the first electrode and the reference electrode and regulating the oxygen concentration with a first oxygen-ion pumping current between the first electrode and the outer electrode;
• measuring an oxygen concentration in the second measuring cell via a second Nernst voltage between the second electrode and the reference electrode;
• and
• with the first and second measuring cells connected in series, picking off a voltage between the outer electrode and the reference electrode, and detecting an output signal dependent on the oxygen concentration and exhibiting two-position behavior during the regeneration phase;
• and
• deriving from a time profile of the output signal a criterion as to whether the quantity of regeneration agent must be changed in order to achieve optimum regeneration of the NOx storage catalyst.