Method for purifying exhaust gas of an internal combustion engine

A method for purifying the exhaust gas from an internal combustion engine which is operated under lambda-based closed loop control and which has an exhaust gas tract in which a catalytic converter is located, comprising:

• continuously sensing a lambda value for the exhaust gas upstream of the catalytic converter, from which a pre-converter lambda signal is generated;
• using the pre-converter signal as a reference variable for the lambda control loop;
• generating a binary post-converter lambda signal by continuously sensing a post-converter lambda value for the exhaust gas downstream from the converter by a binary lambda probe, the binary post-converter lambda signal being a monotonically decreasing function of the lambda value for the exhaust gas downstream from the catalytic converter and having a two-point type graph around lambda=1;
• and
• applying a correction to the lambda control loop by using a trimming controller,
• wherein
• a broadband lambda probe is used to generate a linear post-converter lambda signal which is a strictly monotonic increasing function of the lambda value of the exhaust gas downstream from the catalytic converter,
• the linear post-converter lambda signal is used for trimming control, and
• if the binary post-converter lambda signal has a defined level the actual signal level for the linear post-converter lambda signal is simultaneously determined, the lambda value which has been assigned to the defined binary post-converter signal level is used to determine a corresponding set level for the linear post-converter signal and the trimming control takes into account any difference between the actual signal level and the set signal level as a correction factor.

A method for purifying the exhaust gas from an internal combustion engine which is operated under lambda-based closed loop control and which has an exhaust gas tract in which a catalytic converter is located, comprising:

• continuously sensing a pre-converter lambda value for the exhaust gas upstream of the catalytic converter, from which a pre-converter lambda signal is generated;
• using this pre-converter signal as a reference variable for the lambda control loop;
• continuously sensing a lambda value for the exhaust gas downstream from the converter, from which a post-converter lambda signal is generated, this being a monotonically decreasing function of the lambda value (λ) for the exhaust gas downstream from the catalytic converter;
• and
• applying a correction to the lambda control loop by using this post-converter lambda signal in a trimming control loop, wherein
• a measurement signal is generated which, at least below a certain value of lambda close to lambda=1, is a strictly monotonically increasing or monotonically decreasing function of the lambda value for the exhaust gas downstream from the catalytic converter,
• for levels of the post-converter lambda signal which are above a threshold value, this supplementary measurement signal is used for trimming control, and for levels of the post-converter lambda signal which are below this threshold value, the post-converter lambda signal itself is used for trimming control,
• the post-converter lambda signal is obtained using a binary lambda probe,
• the measurement signal is obtained using a broadband lambda probe and on both sides of lambda=1 is a strictly monotonic increasing function of the lambda value for the exhaust gas,
• the threshold value for the post-converter lambda signal corresponds to a defined lambda value close to lambda=1,
• at the point in time at which the post-converter lambda signal is equal to the threshold value, the difference between the lambda value indicated by the measurement signal and the defined lambda value is determined, and
• this difference is taken into account in the trimming controller if the measurement signal is being used by the trimming controller.