Method for diagnosing a plurality of lambda sensors

Abstract

A method for diagnosing a plurality of lambda sensors which are arranged upstream of an exhaust gas catalytic converter in a plurality of exhaust gas banks of a multi-flow exhaust gas system of an internal combustion engine. An opposite lambda offset of the lambda sensors is identified (54) when a difference (ΔT) between a measured exhaust gas temperature (T.sub.measure) and a modeled exhaust gas temperature (T.sub.mod) downstream of the exhaust gas catalytic converter overshoots a threshold value (S).

Claims

1. A method for diagnosing a plurality of lambda sensors (31, 32) which are arranged in a plurality of exhaust gas banks (21, 22) of a multi-flow exhaust gas system (20) of an internal combustion engine (10), the plurality of exhaust gas banks (21, 22) arranged upstream of an exhaust gas catalytic converter (25), the method comprising: modeling an exhaust gas temperature (T.sub.mod) downstream of the exhaust gas catalytic converter (25); measuring, via a temperature sensor, an exhaust gas temperature (T.sub.measure); identifying (54) an opposite lambda offset of the plurality of lambda sensors (31, 32) when a difference (.DELTA.T) between the measured exhaust gas temperature (T.sub.measure) and the modeled exhaust gas temperature (T.sub.mod) overshoots a threshold value (S), and performing opposite corrections of lambda setpoint values (.lamda..sub.set21, .lamda..sub.set22) of the plurality of exhaust gas banks (21, 22) during the identification (54) of the opposite lambda offset.

2. The method according to claim 1, further comprising ascertaining the difference (.DELTA.T) under stationary operating conditions of the internal combustion engine (10).

3. The method according to claim 1, wherein, the opposite corrections are performed (55) until a minimum (.DELTA.T.sub.min) of the difference (.DELTA.T) between the measured exhaust gas temperature (T.sub.measure) and the modeled exhaust gas temperature (T.sub.mod) is reached.

4. The method according to claim 3, wherein a conclusion is drawn (58) about individual lambda offsets (.lamda..sub.off31, .lamda..sub.off32) of the plurality of lambda sensors (31, 32) from corrected lambda setpoint values (.lamda..sub.set21, .lamda..sub.set22) at the minimum (.DELTA.T.sub.min).

5. The method according to claim 3, further comprising maintaining corrected lambda setpoint values (.lamda..sub.set21, .lamda..sub.set22) at the minimum (.DELTA.T.sub.min) during further operation of the internal combustion engine (10).

6. A non-transitory, computer-readable storage medium containing instructions that when executed on a computer cause the computer to control a multi-flow exhaust gas system (20) having a plurality of lambda sensors (31, 32) arranged in a plurality of exhaust gas banks (21, 22), the plurality of exhaust gas banks (21, 22) arranged upstream of an exhaust gas catalytic converter (25), the multi-flow exhaust gas system (20) being controlled to: model an exhaust gas temperature (T.sub.mod) downstream of the exhaust gas catalytic converter (25); measure, via a temperature sensor, an exhaust gas temperature (T.sub.measure); identify (54) an opposite lambda offset of the plurality of lambda sensors (31, 32) when a difference (.DELTA.T) between the measured exhaust gas temperature (T.sub.measure) and the modeled exhaust gas temperature (T.sub.mod) overshoots a threshold value (S), and perform opposite corrections of lambda setpoint values (.lamda..sub.set21, .lamda..sub.set22) of the plurality of exhaust gas banks (21, 22) during the identification (54) of the opposite lambda offset.

7. An electronic controller (40) for a multi-flow exhaust gas system (20) having a plurality of lambda sensors (31, 32) arranged in a plurality of exhaust gas banks (21, 22), the plurality of exhaust gas banks (21, 22) arranged upstream of an exhaust gas catalytic converter (25), the electronic controller (40) configured to: model an exhaust gas temperature (T.sub.mod) downstream of the exhaust gas catalytic converter (25); measure, via a temperature sensor, an exhaust gas temperature (T.sub.measure); identify (54) an opposite lambda offset of the plurality of lambda sensors (31, 32) when a difference (DELTA.T) between the measured exhaust gas temperature (T.sub.measure) and the modeled exhaust gas temperature (T.sub.mod) overshoots a threshold value (S)), and perform opposite corrections of lambda setpoint values (.lamda..sub.set21, .lamda..sub.set22) of the plurality of exhaust gas banks (21, 22) during the identification (54) of the opposite lambda offset.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) An exemplary embodiment of the invention is illustrated in the drawings and will be explained in greater detail in the following description.

(2) FIG. 1 schematically shows an exhaust gas system, the lambda sensors of which can be diagnosed by means of an exemplary embodiment of the method according to the invention.

(3) FIG. 2 shows a flowchart of an exemplary embodiment of the method according to the invention.

DETAILED DESCRIPTION

(4) An internal combustion engine 10, which drives a motorcycle in the present exemplary embodiment, is illustrated in FIG. 1. The internal combustion engine has two cylinder banks. The exhaust gas system 20 of said internal combustion engine therefore has two exhaust gas banks 21, 22. On account of the limited installation space in the motorcycle, the first exhaust gas bank 21 is shorter than the second exhaust gas bank 22. The two exhaust gas banks 21, 22 of the initially two-flow exhaust gas system 20 are combined at a Y junction 23 to form a common exhaust gas section 24. An exhaust gas catalytic converter 25, which is embodied as a three-way catalytic converter, is arranged in said exhaust gas section. A first lambda sensor 31 is arranged in the first exhaust gas bank 21. A second lambda sensor 32 is arranged in the second exhaust gas bank 22. In the present exemplary embodiment, the two lambda sensors 31, 32 are embodied as broadband lambda sensors. A temperature sensor 33 is arranged in the exhaust gas section 24 downstream of the exhaust gas catalytic converter 25. An electronic controller 40, which controls the internal combustion engine 10, receives sensor data of the two lambda sensors 31, 32 and of the temperature sensor 33.

(5) As is illustrated in FIG. 2, after starting 50 of an exemplary embodiment of the method according to the invention, a check 51 is initially made in respect of whether the internal combustion engine 10 is under stationary operating conditions, this being the case when the motorcycle is under stationary driving conditions. If this condition is satisfied, a difference ΔT between a measured exhaust gas temperature T.sub.measure and a modeled exhaust gas temperature T.sub.mod is calculated 52 upstream of the exhaust gas catalytic converter 25. The measured exhaust gas temperature T.sub.measure is measured by means of the temperature sensor 33. The modeled exhaust gas temperature T.sub.mod is subtracted from said measured exhaust gas temperature. Said modeled exhaust gas temperature is taken from a temperature model which does not contain any information about possible lambda offsets of the two lambda sensors 31, 32. The difference ΔT is compared with a threshold value S which is 30 Kelvins in the present exemplary embodiment. If the difference ΔT overshoots the threshold value S, it is identified 54 that there is an opposite lambda offset between the two lambda sensors 31, 32. In the text which follows, it is assumed that there is a positive lambda offset of the first lambda sensor 31 and a negative lambda offset of the second lambda sensor 32.

(6) Opposite corrections 55 of the lambda setpoint value λ.sub.set21 of the first exhaust gas bank 21 and of the lambda setpoint value λ.sub.set22 of the second exhaust gas bank 22 of the internal combustion engine 10 are now performed several times. Opposite corrections are carried out here by way of one of the lambda setpoint values always being increased and the other lambda setpoint value being lowered. After each correction 55, recalculation 56 of the difference ΔT is performed in the same way as was also carried out in step 52. If a pair of corrected lambda setpoint values λ.sub.set21, λ.sub.set22 was found after several repetitions of the corrections 55, in which pair the difference ΔT reaches a minimum ΔT.sub.min in comparison to all other corrections which were carried out, a conclusion is drawn 58 about the individual lambda offsets λ.sub.off31, λ.sub.off32 of the two lambda sensors 31, 32 from the corrected lambda setpoint values λ.sub.set21, λ.sub.set22 at the minimum ΔT.sub.min. When the first lambda sensor 31 has a positive lambda offset and the second lambda sensor 32 has a negative lambda offset, the lambda setpoint value λ.sub.set21 of the first exhaust gas bank 21 then lies above its uncorrected value by the lambda offset λ.sub.off31 of the first lambda sensor 31 at the minimum ΔT.sub.min. The lambda setpoint value λ.sub.set22 of the second exhaust gas bank 22 then lies above the uncorrected lambda setpoint value of the second exhaust gas bank 22 by the lambda offset λ.sub.off32 of the second lambda sensor 32. The method is then ended 59 and the operation of the internal combustion engine 10 is continued with the corrected lambda setpoint values λ.sub.set21, λ.sub.set22. In this way, there are no longer any deviations in the fuel/air mixture formation of the two exhaust gas banks of the internal combustion engine 10, so that there are also no longer any undesired increases in temperature in the exhaust gas catalytic converter 25 due to chemical reactions between rich and lean exhaust gas constituents hereinafter. Since the lambda offsets λ.sub.off31, λ.sub.off32 are now known, these can also be taken into account in the temperature model, so that the measured exhaust gas temperature T.sub.measure no longer deviates from the modeled exhaust gas temperature T.sub.mod.