Method for on-board diagnosis of an oxidation catalyst in an exhaust-gas system of an internal combustion engine of a vehicle

Abstract

A method for on-board diagnosis of an oxidation catalyst in an exhaust-gas system of an internal combustion engine of a vehicle having an engine control device and a temperature sensor in the exhaust gas system upstream from a downstream side of said oxidation catalyst. The method includes operating the internal combustion engine is in an overrun mode, and injecting a quantity of fuel upstream from the oxidation catalyst. The change of temperature values over time is measured by the temperature sensor, and at least one physical quantity that characterizes the heat release in said oxidation catalyst is calculated on the basis of said amount of injected fuel. The method further includes ascertaining whether the calculated quantity falls within a set of values, and, if so, declaring that said oxidation catalyst is considered to be defective.

1 . A method for on-board diagnosis of an oxidation catalyst in an exhaust-gas system of an internal combustion engine of a vehicle, wherein the vehicle has an engine control device and a temperature sensor located in the exhaust gas system upstream from a downstream side of said oxidation catalyst, said method comprising the following steps:
 operating said internal combustion engine in an overrun mode;   injecting an amount of fuel upstream from said oxidation catalyst;   measuring, via said temperature sensor, a change of temperature values over time;   calculating, via said engine control device, at least one physical quantity that characterizes a heat release in said oxidation catalyst on the basis of said amount of injected fuel;   determining, via said engine control device, whether the calculated quantity falls within a set of values; and   declaring, via said engine control device, that said oxidation catalyst is defective if the calculated quantity falls within the set of values.   
     
     
         2 . The method for the on-board diagnosis of an oxidation catalyst according to  claim 1 , whereby declaring that said oxidation catalyst is defective comprises generating an error signal in said engine control device. 
     
     
         3 . The method for the on-board diagnosis of an oxidation catalyst according to  claim 1 , wherein measuring the change of temperature values comprises measuring the change at a predetermined location in the oxidation catalyst. 
     
     
         4 . The method for the on-board diagnosis of an oxidation catalyst according to  claim 1 , wherein said at least one physical quantity is a measure of a thermal energy released in said oxidation catalyst corresponding to said amount of injected fuel. 
     
     
         5 . The method for the on-board diagnosis of an oxidation catalyst according to  claim 4 , further comprising, determining, during the calculation of said physical quantity, differences between the measured temperature values and reference temperature values. 
     
     
         6 . The method for the on-board diagnosis of an oxidation catalyst according to  claim 1 , wherein said at least one physical quantity is a measure of a temperature gradient, or said at least one physical quantity is a quantity change that is a measure of a change of values of temperature gradients. 
     
     
         7 . The method for the on-board diagnosis of an oxidation catalyst according to  claim 1 , wherein a temperature threshold is prescribed for a measured temperature, and further comprising determining a time span until the measured temperature exceeds the temperature threshold, wherein the determined time span is said at least one physical quantity. 
     
     
         8 . The method for the on-board diagnosis of an oxidation catalyst according to  claim 1 ,
 wherein calculating at least one physical quantity comprises calculating a plurality of physical quantities, and   wherein each physical quantity constitutes a measure of a physical quantity of a chemical conversion, and the plurality of physical quantities are mutually different from one another.   
     
     
         9 . The method for the on-board diagnosis of an oxidation catalyst according to  claim 8 , wherein the plurality of physical quantities comprises one, several or all of the physical quantities selected from the group consisting of: a measure of thermal energy released in said oxidation catalyst on the basis of said amount of injected fuel, a measure of a temperature gradient, a measure of a change of values of temperature gradients, and a measure of a time span until a measured temperature has exceeded a temperature threshold. 
     
     
         10 . A vehicle having
 an internal combustion engine,   an exhaust-gas system with an oxidation catalyst, and   an engine control device comprising at least one computer and at least one memory element, wherein said engine control device is configured to carry out the method for the on-board diagnosis of the oxidation catalyst according to  claim 1  during at least a partial execution of said computer.