Method and system for diagnosing an aftertreatment system

1. A method for diagnosing aftertreatment of exhaust gases resulting from combustion, wherein at least a first substance resulting from said combustion is reduced by supplying additive to an exhaust gas stream resulting from said combustion and use of a first reduction catalytic converter, the method comprising:

estimating an accumulated expected reduction of said first substance during a first period of time on the basis of a measure of quality of said additive, said measure of quality being determined by means of a quality sensor being subjected to said additive;

determining an accumulated actual reduction of said first substance during a period of time at least substantially overlapping said first period of time; and

generating a signal indicating a fault in said reduction of said first substance when said accumulated actual reduction differs from said accumulated expected reduction by a predetermined difference in occurrence of said first substance.

2. A method according to claim 1 , further comprising:

determining a first accumulated supply of additive during said first period of time; and

estimating said accumulated expected reduction of said first substance further on the basis of said first accumulated supply of additive.

3. A method according to claim 1 , further comprising:

determining said accumulated reductions as accumulated quantities of said first substance.

4. A method according to claim 3 , further comprising:

determining said accumulated reductions as quantities being reduced or quantities remaining in the exhaust gas stream following reduction.

5. A method according to claim 2 , further comprising determining said first accumulated supply of additive by determining a decrease in a degree of filling in a tank containing said additive.

6. A method according to claim 2 , further comprising determining said first accumulated supply of additive from injection pressure and opening time of an injection nozzle injecting said additive into said exhaust gas stream.

7. A method according to claim 1 , further comprising:

determining said accumulated actual reduction by determining the presence or occurrence of the substance to be reduced upstream the supply of additive; and

comparing this occurrence with a measured occurrence downstream the supply of additive.

8. A method according to claim 7 , further comprising determining said presence or occurrence of the substance to be reduced upstream the supply of additive by means of a model and/or use of a sensor located upstream the supply of additive.

9. A method according to claim 7 , further comprising determining said presence or occurrence of the substance to be reduced while additive is supplied to said exhaust gas stream.

10. A method according to claim 7 , further comprising determining said presence or occurrence of the substance to be reduced continuously during the period of time for which the actual reduction is accumulated.

11. A method according to claim 1 , further comprising generating a signal indicating a fault when said comparison indicates that an actual occurrence of said first substance following said reduction exceeds said accumulated expected occurrence of said first substance following said reduction by a predetermined difference in occurrence.

12. A method according to claim 1 , further including accumulating said reduction at least during a time period in the interval 2 minutes to four hours.

13. A method according to claim 1 , further comprising:

determining said first accumulated supply of additive from injection pressures and opening times of an injection nozzle injecting said additive into said exhaust gas stream;

when said accumulated actual reduction deviates from said accumulated expected reduction by said predetermined difference in occurrence of said first substance,

determining a second accumulated supply of additive by determining a reduction of a degree of filling in a tank containing said additive during a second period of time, said second period of time being longer than said first period of time; and

generating said signal indicating a fault in the reduction when, following said second period of time, said accumulated actual reduction deviates from said accumulated expected reduction by said predetermined difference in occurrence of said first substance.

14. A method according to claim 1 , further comprising determining said actual reduction of said first substance by means of a measure of said occurrence of said first substance downstream said reduction catalytic converter, said measure being determined by means of sensor means.

15. A method according to claim 1 , further comprising, when said signal indicating a fault in the reduction is generated:

performing a first test of sensor means measuring said occurrence of said first substance in said exhaust gas stream to evaluate operation of said sensor means; and

generating a signal indicating sensor means fault when said evaluation of the operation of said sensor means indicates improper operation of said sensor means.

16. A method according to claim 1 , further comprising, when said signal indicating a fault in the reduction is generated:

performing a test of consumption of additive, including:

determining a further accumulated supply of additive from injection time and injection pressure of an injection nozzle; and

comparing said further accumulated supply of additive with a consumption of additive determined by measurement means arranged in a tank containing said additive; and

generating a signal indicating a fault in consumption of additive when said further accumulated supply of additive and said consumption of additive determined by said measurement means differs by a predetermined amount of additive.

17. A computer program product stored on a non-transitory computer-readable medium, said computer program product for diagnosing aftertreatment of exhaust gases resulting from combustion, wherein at least a first substance resulting from said combustion is reduced by supplying additive to an exhaust gas stream resulting from said combustion and use of a first reduction catalytic converter, said computer program product comprising computer instructions to cause one or more electronic control units or computers to perform the following operations:

estimating an accumulated expected reduction of said first substance during a first period of time on the basis of a measure of quality of said additive, said measure of quality being determined by means of a quality sensor being subjected to said additive;

determining an accumulated actual reduction of said first substance during a period of time at least substantially overlapping said first period of time; and

generating a signal indicating a fault in said reduction of said first substance when said accumulated actual reduction differs from said accumulated expected reduction by a predetermined difference in occurrence of said first substance.

18. A system for diagnosing aftertreatment of exhaust gases resulting from combustion, wherein at least a first substance resulting from said combustion is reduced by supplying additive to an exhaust gas stream resulting from said combustion and use of a first reduction catalytic converter, the system comprising:

means for estimating an accumulated expected reduction of said first substance during a first period of time on the basis of a measure of quality of said additive, said measure of quality being determined by means of a quality sensor being subjected to said additive;

means for determining an accumulated actual reduction of said first substance during a period of time at least substantially overlapping said first period of time; and

means for generating a signal indicating a fault in said reduction of said first substance when said accumulated actual reduction differs from said accumulated expected reduction by a predetermined difference in occurrence of said first substance.

19. A vehicle comprising a system for diagnosing aftertreatment of exhaust gases resulting from combustion, wherein at least a first substance resulting from said combustion is reduced by supplying additive to an exhaust gas stream resulting from said combustion and use of a first reduction catalytic converter, the system comprising:

means for estimating an accumulated expected reduction of said first substance during a first period of time on the basis of a measure of quality of said additive, said measure of quality being determined by means of a quality sensor being subjected to said additive;

means for determining an accumulated actual reduction of said first substance during a period of time at least substantially overlapping said first period of time; and

means for generating a signal indicating a fault in said reduction of said first substance when said accumulated actual reduction differs from said accumulated expected reduction by a predetermined difference in occurrence of said first substance.