Method and device for monitoring a nitrogen oxide trap

1. A method for monitoring a nitrogen oxide trap in an exhaust tract of a motor vehicle with an internal combustion engine, the method comprising:

immediately after performing a regeneration of the nitrogen oxide trap, determining a residual capacity of the nitrogen oxide trap;

if the residual capacity is below a predefined threshold, deactivating nitrogen oxide trap regeneration going forward;

implementing at least one remedial action selected from the group consisting of: filtering nitrogen oxide from the exhaust tract using an SCR catalytic converter and applying heat to the SCR catalytic converter; and

reactivating nitrogen oxide trap regeneration upon detection of a refueling event.

2. The method as claimed in claim 1 , the method further comprising comparing a second threshold value with a storage capacity value before adding fuel to a fuel tank of the motor vehicle; and

only deactivating the nitrogen oxide trap regeneration if the storage capacity value is at least twice the second threshold value.

3. The method as claimed in claim 1 , wherein:

determining a reduction rate of the storage capacity;

determining a sulfur content in a fuel as a function of the reduction rate;

comparing the sulfur content with a predefined sulfur threshold value; and

if the sulfur threshold value is exceeded, deactivating the nitrogen oxide trap regeneration.

4. The method as claimed in claim 3 , wherein the sulfur content in the fuel is determined by means of a predefined sulfur model as a function of an injected quantity of fuel over time.

5. The method as claimed in claim 3 , wherein the sulfur threshold value is 200 ppm.

6. The method as claimed in claim 1 , wherein the refueling event includes refueling the motor vehicle with at least a predefined quantity of fuel.

7. The method as claimed in claim 6 , wherein the predefined quantity of fuel is four times a residual quantity of fuel stored in a fuel tank of the motor vehicle.

8. The method as claimed in claim 3 , further comprising signaling to a driver of the motor vehicle that refueling has been carried out with a sulfur-rich fuel in response to exceeding the sulfur threshold value.

9. The method as claimed in claim 3 , further comprising:

after reactivating nitrogen oxide trap regeneration, determining the sulfur content in the fuel again;

comparing the re-determined sulfur content with a second sulfur threshold value; and

if the second sulfur threshold value is exceeded, deactivating nitrogen oxide trap regeneration again.

10. The method as claimed in claim 9 , further comprising deactivating a signal to a driver of a vehicle associated with the nitrogen oxide trap in response to undershooting the second sulfur threshold value; and

continuing the signal in response to overshooting the second sulfur threshold value.

11. The method as claimed in claim 9 , wherein the second sulfur threshold value is 50 ppm.

12. A motor vehicle comprising:

a combustion chamber;

an exhaust tract for gasses leaving the combustion chamber;

a nitrogen oxide trap disposed to remove nitrogen oxide from gasses flowing through the exhaust tract; and

a controller monitoring the nitrogen oxide trap, the controller programmed to:

immediately after performing a regeneration of the nitrogen oxide trap, determine a residual capacity of the nitrogen oxide trap;

if the residual capacity is below a predefined threshold, deactivate nitrogen oxide trap regeneration going forward;

implement at least one remedial action selected from the group consisting of: filtering nitrogen oxide from the exhaust tract using an SCR catalytic converter and applying heat to the SCR catalytic converter; and

reactivate nitrogen oxide trap regeneration upon detection of a refueling event.