DE102005056312A1 - Examination of conversion ability of catalyst of combustion engine, involves deriving conversion ability of catalyst from measured value deviation of probe signal of broadband lambda probe arranged downstream to catalyst - Google Patents

Abstract

The invention relates to a method for checking the convertibility of a catalytic converter of an internal combustion engine with regard to at least one pollutant component of a lean exhaust gas with lambda> 1. From a measured value deviation DELTAlambda of a probe signal lambda¶SONDE¶ of a broadband lambda probe arranged downstream of the catalytic converter from an actual lambda -Value lambda¶ist¶ of the exhaust gas downstream of the catalytic converter, the conversion capacity of the catalytic converter is derived.

Description

The The invention relates to a method for checking the conversion capability a catalytic converter of an internal combustion engine with regard to at least one Pollutant component of a lean exhaust gas with λ> 1.

In order to in a, an internal combustion engine downstream catalyst high Conversion rates of pollutants in the exhaust gas of the internal combustion engine can be achieved must in engine management for it be ensured that a lambda value is maintained within a narrow range becomes. The engine management needed for controlling the mixture composition and thus the exhaust gas composition a transmitter, with the help of which the residual oxygen content of the Exhaust gas can be measured before the catalyst. The transmitter is usually a lambda probe before the catalyst, which the Oxygen content in the exhaust gas by a comparative measurement with the Oxygen content of the outside air determined as reference value.

to Compliance with the ever stricter emission standards is also a monitoring of operability the catalyst necessary, since damage to the catalyst, the pollutant emission significantly increase can.

To monitor and diagnose the functionality of the catalysts of gasoline engines are from the DE 41 12 478 and the DE 42 09 136 Known method, the oxygen storage capacity, which correlates with the hydrocarbon conversion in the catalyst use. To determine whether the warm catalyst sufficiently converts the pollutants, a second lambda probe is installed as a monitor after the catalyst. Due to the continuous control of the mixture composition, oxygen scavenging occurs in front of the catalyst, which causes voltage jumps in the lambda probe upstream of the catalytic converter. With a high storage capacity of the catalyst is hardly oxygen in the exhaust gas and the monitor probe indicates a nearly constant voltage. If the condition of the catalyst deteriorates, the monitor probe also shows voltage jumps. The determined oxygen storage capacity is correlated with the catalyst conversion and the emission behavior. The diagnosis of the functionality of the catalysts from the sensor signals is thereby relatively complicated and tedious.

Around the pollutant emission and consumption of internal combustion engines To further reduce, so-called lean-burn engines are used. These work in contrast to usual Otto engines with an excess of oxygen (Lambda »1) when burning. The supervision the catalyst therefore requires a sensor, the oxygen components can still reliably detect up to 8% in the exhaust gas. The conventional binary Lambda probe is for the Optimized use in gasoline engine, in which a jump in oxygen content to detect many decades. For operation in lean lambda ranges with λ »1 is enough the accuracy of conventional binary Probes not because of the permanent oxygen content in the Exhaust gas no usable signal with sufficient resolution output becomes.

The The object of the invention is therefore a simple and reliable verification of the functionality of catalysts in a lean operation mode enable.

The The object is achieved by a Method according to claim 1 solved. Further advantageous embodiments are the dependent claims refer to.

In the method according to the invention, in order to check the conversion capability of a catalytic converter of an internal combustion engine with respect to at least one pollutant component of a lean exhaust gas with λ> 1, a measured value deviation Δλ of a probe signal λ _{PRODE of} a broadband lambda probe arranged downstream of the catalytic converter _results from an actual lambda value λ _is the exhaust gas downstream of the catalyst, the conversion capability of the catalyst derived.

With The broadband lambda probe can have lambda values be measured continuously between 0.8 and 2.5. This is possible because a nearly linear "pumping current" serves as a measured variable. The broadband probe has two cells, a pump cell and a Sensor cell. With the pumping current always so many oxygen ions pumped into the measuring chamber until it is between the electrodes in the reference air channel and in the measuring cell a concrete voltage value has set. The pumping current is the measured variable for the lambda value.

According to the invention, the limited reaction kinetics of a broadband lambda probe is used to check the conversion capability of a catalyst. In a catalyst having reduced conversational ability, the exhaust gas still contains a large amount of hydrocarbons after passing through the catalyst. Since the hydrocarbons on the probe surface are not oxidized fast enough, an excess of oxygen remains at the probe surface, which is detected. As a result, the probe signal λ _{probe shows} more oxygen in the exhaust gas than is actually present. From the measured value deviation Δλ λ of the probe signal _PROBE from the actual lambda actual value λ of the _exhaust gas is on the conversion efficiency the catalyst is closed.

The lambda actual value λ _is the exhaust gas is preferably by means of a probe which detects the oxygen content in the exhaust gas with a different measuring principle as the broadband lambda probe, measured or calculated from models.

The method preferably checks the conversion ability of an oxidation catalyst. In the oxidation catalytic converter, the pollutants HC and CO are converted into H ₂ O and CO ₂ with the residual oxygen or with additional air introduced into the exhaust gas. A reduction of the nitrogen oxides takes place in a downstream NO _x adsorber. The case downstream of the catalyst or NO _x adsorber arranged NO _x sensor is preferably the same for detecting the lambda actual value λ of the exhaust gas _is used. Since the NO _x sensor is a dual-chamber sensor, it measures the lambda value of the exhaust gas on the one hand and the nitrogen oxide reduction on the other.

In a further advantageous embodiment of the method, the lambda actual value λ _{ist of} the exhaust gas is detected with an amperometric oxygen sensor. Amperometric oxygen sensors are gas diffusion limit current probes and are based on an electrochemical. Oxygen pumping cell, preferably zirconium oxide. When a voltage is applied to the cells, oxygen ions are pumped from the cathode to the anode. If, in addition, the cathode is covered with a gas diffusion barrier, as the voltage is increased, a saturation current is established, which is a measure of the oxygen concentration in the exhaust gas.

In a further advantageous embodiment of the method, the lambda actual value λ _is the exhaust gas with an oxygen sensor with a metal oxide sensor layer whose conductivity is dependent on the oxygen content in the exhaust detected. Preferably, oxygen sensors are used with a metal oxide sensor layer based on copper or on the basis of erdalkalidotierter Lanthanferrite, since they have a low temperature dependence.

Alternatively or additionally, the lambda actual value λ _{ist of} the exhaust gas can preferably be calculated from a model. For this purpose, known model calculations, for example, can be used.

The The invention will be further explained with reference to an embodiment.

It should the conversion ability with regard to the pollutants HC and CO of an oxidation catalyst be checked under an OBD. to Making the measurement conditions can be a short-term exhaust gas deterioration by HC feed be set.

Downstream of the oxidation catalytic converter, a broadband lambda sensor of the LSU type is arranged, from which the probe signal λ _{PROBE is} detected as the value for the oxygen concentration in the exhaust gas and forwarded to the engine controller.

As a reference value for determining the measurement deviation Δλ of the probe signal λ _probe, a lambda actual value _is λ from the signal from a NO _x probe detected with integrated oxygen measurement capability of the type NGK and forwarded to the engine control.

For the comparability of the lambda value from the probe signal λ _{PROBE of} the broadband lambda probe with the lambda actual value λ _, the NO _x probe, the values are adjusted by means of calibration curves stored in the engine control.

By Difference formation is determined from the calibrated values Measurement deviation Δλ calculated and the conversion ability derived in terms of pollutants HC and CO.

Claims (6)

Method for checking the conversion capability of a catalytic converter of an internal combustion engine with respect to at least one pollutant component of a lean exhaust gas with λ> 1, characterized in that from a measured value deviation Δλ a probe signal λ _PROBE a wide- _band lambda probe arranged downstream of the catalyst of an actual lambda value λ _is the exhaust gas. downstream of the catalyst, the conversion capability of the catalyst is derived. A method according to claim 1, characterized in that the lambda actual value λ _is detected of the exhaust gas with a NO _x sensor. A method according to claim 1, characterized in that the lambda actual value λ _is detected in the exhaust gas with an amperometric oxygen sensor. A method according to claim 1, characterized in that the lambda actual value λ _is the exhaust gas with an oxygen sensor with a metal oxide sensor layer whose conductivity is dependent on the oxygen content in the exhaust gas is detected. Method according to one of the preceding claims, characterized in that the lambda actual _value λ of the exhaust gas is calculated from a model. Method according to one of the preceding claims, characterized characterized in that the conversion ability of an oxidation catalyst is checked.