Method and device for determining the oxygen storage capacity of an emission control system

#The present application claims the benefit under 35 U.S.C. §119 of German Patent Application No. DE102013201228.4 filed on Jan. 25, 2013, which is hereby incorporated by reference in its entirety.

#The present invention relates to a method for determining the oxygen storage capacity of an emission control system in an exhaust duct of an internal combustion engine, having a first exhaust gas analyzer probe situated in front of the emission control system in a direction of flow and a second exhaust gas analyzer probe situated in back of the emission control system; in a first phase, the internal combustion engine being operated at an air-fuel mixture having a rich (λ<1) air-to-fuel ratio, and in a second phase, the engine being operated using a lean (λ>1) air-to-fuel ratio; and an oxygen storage capacity of the emission control system being determined from an oxygen input into the emission control system during the second phase; and/or in order to determine a hydrocarbon gas storage capacity, the internal combustion engine being operated during the first phase at a lean (λ>1) air-to-fuel ratio, and operated in the second phase at a rich (λ<1) air-to-fuel ratio; and the hydrocarbon gas storage capacity being determined from the oxygen discharge from the emission control system during the second phase.

#The present invention further relates to a device for determining the oxygen storage capacity of an emission control system in an exhaust duct of an internal combustion engine, having a first exhaust gas analyzer probe situated in front of the emission control system in a direction of flow, a second exhaust gas analyzer probe situated in back of the emission control system, and an engine control unit assigned to the internal combustion engine; the engine control unit including a circuit or a program sequence, with the aid of which the air-fuel mixture supplied to the engine is controlled in such a manner, that in a first phase, the engine is operated using an air-fuel mixture having a rich (λ<1) air-to-fuel ratio and having, and in a second phase, the engine is operated at a lean (λ>1) air-to-fuel ratio, and that an oxygen storage capacity of the emission control system is determined from an oxygen input into the emission control system during the second phase, and/or that to determine a hydrocarbon gas storage capacity, the engine is operated during the first phase at a lean (λ>1) air-to-fuel ratio, and operated in the second phase at a rich (λ<1) air-to-fuel ratio; and the engine control unit including a program sequence for determining the hydrocarbon gas storage capacity from the oxygen discharge from the emission control system during the second phase.

#FIG. 1 shows a schematic view of the technical field in which the example method of the present invention may be used.

#FIG. 2 shows a graph including signal characteristics in the case of a sudden change in lambda.

#Using an example of a spark ignition engine, FIG. 1 schematically shows the technical field in which the example method of the present invention for determining the oxygen storage capacity of an emission control system 17 may be used. An internal combustion engine 10 is fed air via an air supply line 11, and its mass is determined by an air mass meter 12. Air mass meter 12 may take the form of a hot-film air mass meter. The exhaust gas of the internal combustion engine 10 is removed via an exhaust duct 16; emission control system 17 being provided in back of internal combustion engine 10 in the direction of flow of the exhaust gas. In order to control internal combustion engine 10, an engine control unit 14 is provided, which, first of all, controls the amount of fuel supplied to internal combustion engine 10 via a fuel meter 13 and, secondly, is supplied the signals of air mass meter 12 and of a first exhaust gas analyzer probe 15 situated in exhaust duct 16, in front of emission control system 17, as well as of a second exhaust gas analyzer probe 18 situated in exhaust duct 16, in back of emission control system 17. Exhaust gas analyzer probe 15 determines an actual lambda value of a fuel-air mixture supplied to internal combustion engine 10 and is part of a lambda control loop assigned to internal combustion engine 10. It may take the form of a wide-range lambda probe or linear lambda probe. Second exhaust gas analyzer probe 18 determines the composition of the exhaust gas downstream from emission control system 17. Second exhaust gas analyzer probe 18 may take the form of a step change probe or binary probe.

#During a preconditioning, internal combustion engine 10 is driven at a rich air-to-fuel ratio (λ<1) to determine the oxygen storage capacity of emission control system 17. In this context, the oxygen is completely removed from emission control system 17. The end of the preconditioning is achieved, when second exhaust gas analyzer probe 18 indicates the breakthrough of rich exhaust gas. In a following measuring phase, internal combustion engine 10 is driven at a lean air-to-fuel ratio (λ>1). The lean exhaust gas arrives at emission control system 17 with a slight delay, and the oxygen contained in it is stored there. The end of the measuring phase is reached, when the second exhaust gas analyzer probe 18 situated in back of the catalytic converter signals the breakthrough of the lean mixture. The integrated oxygen input during the measuring phase corresponds to the oxygen storage capacity of emission control system 17 and may be used for monitoring the correct functioning of emission control system 17.

#In a graph 20, FIG. 2 shows signal characteristics at different dynamic responses of an oxygen sensor, such as one of the exhaust gas analyzer probes 15, 18 from FIG. 1. A lambda characteristic 23 including a step change from a low lambda value less than 1 to a high lambda value greater than 1 is drawn into diagram 20, along a time axis 31 and along a signal axis 21. For purposes of orientation, a line having a lambda=1 value 22 is drawn in. In response to the sudden change in the air-fuel mixture supplied to internal combustion engine 10 in accordance with lambda characteristic 23, a lambda characteristic subject to a path delay Tn and a path time constant τn is generated at the location of first oxygen sensor 15, in accordance with a first lambda signal 27. First lambda signal 27 increases as of a first time 24 and crosses lambda=1 value 22 at a third time 26. Both first-time 24 and third time 26 are situated after the sudden increase in lambda characteristic 23. The path of first lambda signal 27 may be described by the formula: