Method and control assembly for operating an exhaust gas system
A method for operating an exhaust gas system is provided. The method includes determining an amount of a reducing agent to be supplied to the exhaust gas of an engine and evaluating measurements which indicate a content of nitrogen oxides in the exhaust gas downstream of a catalytic device adapted to diminish the content of nitrogen oxides. A magnitude and a frequency of the measurements are taken into account in determining the amount of the reducing agent to be supplied. A plurality of measurements is captured during a predetermined period of time. A magnitude of a measurement captured within this period of time is related to a quantity derived from the respective magnitudes of the plurality of measurements. The related measurement is utilized to determine the amount of the reducing agent to be supplied. A control assembly for operating an exhaust gas system is also provided.
1. A method for operating an exhaust gas system, the method comprising the steps of:
receiving a signal reading from a nitrogen oxide sensor over a total data sampling time period (τ), wherein the nitrogen oxide sensor measures a content of nitrogen oxides in exhaust gas flowing downstream of a catalytic device configured to diminish the content of nitrogen oxides in the exhaust gas;
obtaining a difference (x i −x s ) between a sampled tail pipe nitrogen oxide concentration (x i ) and a median tail pipe nitrogen oxide concentration (x s ) repeatedly over the total data sampling time period;
determining a lumped average relative magnitude frequency (LARMF) by way of a first relationship,
LARMF
=
1
τ
∫
0
τ
x
i
-
x
s
d
t
;
establishing a second relationship between the lumped average relative magnitude frequency and a reduction in percent of reducing agent relative to a normal supply of the reducing agent; and
adjusting said reduction of reducing agent relative to said normal supply in accordance with said second relationship.
2. The method according to claim 1 , wherein a moving median is utilized as the median tail pipe nitrogen oxide concentration (x s ), which takes into account a series of predetermined periods of time.
3. The method according to claim 1 , wherein a lower lumped average relative magnitude frequency threshold above zero and an upper lumped average relative magnitude frequency threshold are defined, and an amount of reducing agent to be supplied to the exhaust gas is varied if the total is below the lower threshold or above the upper threshold.
4. The method according to claim 3 , wherein the lower lumped average relative magnitude frequency threshold is between 0.1 and 1, and the upper lumped average relative magnitude frequency threshold is between 0.9 and 1.5.
5. The method according to claim 4 , wherein the lower lumped average relative magnitude frequency threshold is between 0.3 and 0.8, and the upper lumped average relative magnitude frequency threshold is between 1 and 1.4.
6. The method according to claim 4 , wherein the lower lumped average relative magnitude frequency threshold is between 0.4 and 0.6, and the upper lumped average relative magnitude frequency threshold is between 1.2 and 1.3.
7. The method according to claim 3 , wherein the amount of the reducing agent to be supplied to the exhaust gas is varied by a PID controller.
8. The method according to claim 1 , wherein receiving the signal reading from the nitrogen oxide sensor occurs repeatedly in a range of 5 seconds to 60 seconds.
9. The method according to claim 8 , wherein receiving the signal reading from the nitrogen oxide sensor occurs repeatedly in the range of 10 seconds to 30 seconds.
10. The method according to claim 8 , wherein receiving the signal reading from the nitrogen oxide sensor occurs repeatedly for 20 seconds.
11. The method according to claim 1 , wherein the total data sampling time period is in a range of 2 minutes to 20 minutes.
12. The method according to claim 1 , wherein the total data sampling time period is in a range of 5 minutes to 15 minutes.
13. The method according to claim 1 , wherein the total data sampling time period is 10 minutes.
14. The method according to claim 1 , wherein the exhaust gas system is of a vehicle.
15. A control assembly for operating an exhaust gas system comprising:
an injector to supply an amount of a reducing agent to exhaust gas of the exhaust gas system of an engine, and
a controller for executing stored instructions to:
receive a signal reading from a nitrogen oxide sensor over a total data sampling time period (τ), wherein the nitrogen oxide sensor measures a content of nitrogen oxides in exhaust gas flowing downstream of a catalytic device configured to diminish the content of nitrogen oxides in the exhaust gas,
determine a lumped average a relative magnitude frequency (LARMF) by way of a first relationship,
LARMF
=
1
τ
∫
0
τ
x
i
-
x
s
d
t
;
establish a second relationship between the lumped average relative magnitude frequency and a reduction in percent of reducing agent relative to a normal supply of the reducing agent; and
adjust said reduction of reducing agent relative to said normal supply in accordance with said second relationship.
16. The control assembly according to claim 15 , wherein the exhaust gas system is of a vehicle.