Method and device for adjustment of a fuel/air ratio for an internal combustion engine

Abstract

In a method for adjusting the fuel/air ratio in an internal combustion engine ( 1 ) comprising a converter ( 2 ) which is associated therewith, a composition of waste gas in the waste gas wing ( 3, 8 ) of the internal combustion engine ( 1 ) is detected by means of sensors ( 4, 5 ) and output signals from at least one of the sensors ( 4, 5 ) are used for producing a control signal in order to influence the fuel/air ratio. The fuel/air ratio is switched back and forth between a lean operating state with surplus oxygen and a rich operating state with an oxygen deficit by means of a characteristic line of the control signal. The characteristic line of the control signal is adapted to a current converter state. A characteristic curve contour of the characteristic line is adjusted according to the addition and/or desorption of an oxidation agent in the converter ( 2 ). The invention also relates to a device for carrying out said method.

1 . A method for adjustment of a fuel/air ratio for an internal combustion engine with an associated catalyst, comprising the steps of: 
 determining an exhaust composition in an exhaust system of the internal combustion engine by means of sensors,    generating a control signal to influence the fuel/air ratio as a function of output signals of at least one of the sensors, and    making by means of a characteristic curve of the control signal a switch back and forth between an operating state with oxygen excess and an operating state with oxygen deficiency of the catalyst, wherein a shape of the characteristic curve is adjusted as a function of an oxygen and/or NO x  addition and/or desorption capability of the catalyst.    
     
     
         2 . A method according to  claim 1 , wherein a course of a transition from operating state to another and/or a course of the characteristic curve within an operating state is adjusted as a function of oxygen and/or NO x  addition and/or desorption capability of the catalyst.  
     
     
         3 . A method according to  claim 1 , wherein the characteristic curve of the control signal is adjusted as a function of a catalyst temperature.  
     
     
         4 . A method according to  claim 1 , wherein the characteristic curve of the control signal is adjusted as a function of the degree of aging of the catalyst.  
     
     
         5 . A method according to  claim 1 , wherein adjustment of the characteristic curve of the control signal occurs as a function of the operating parameters of an internal combustion engine.  
     
     
         6 . A method according to  claim 1 , wherein the characteristic curve of the control signal is adjusted unsymmetrically to a stipulated lambda value over a time range that includes at least several periods of the control signal.  
     
     
         7 . A method according to  claim 1 , wherein the characteristic curve of the control signal is a sawtooth.  
     
     
         8 . A method according to  claim 1 , wherein the subsequent operating states are adjusted with different residence time of the control signal.  
     
     
         9 . A method according to  claim 1 , wherein the subsequent operating states are adjusted with different amplitude of the control signal.  
     
     
         10 . A method according to  claim 1 , wherein the characteristic curve of the control signal is nonlinear at least in a region.  
     
     
         11 . A method according to  claim 10 , wherein the characteristic curve of the control signal becomes leaner or richer degressively.  
     
     
         12 . A method according to  claim 11 , wherein the characteristic of the control signal initially becomes leaner around a stipulated amount or richer and then is degressively guided in the direction λ=1.00.  
     
     
         13 . A method according to  claim 1 , wherein the characteristic curve of the control signal is a rectangular curve with different amplitudes and/or residence times in the adjusted operating states.  
     
     
         14 . A method according to  claim 1 , wherein during fuel cutoff in the overrun or idle of the internal combustion engine, the internal combustion engine is operated more in the rich operating state than in the lean operating state.  
     
     
         15 . A method according to  claim 1 , wherein in a catalyst the control signal is adjusted so that increased incorporation of oxygen and/or NO x  in the catalyst occurs temporarily.  
     
     
         16 . A method according to  claim 1 , wherein in a catalyst after a stipulated operating time the control signal is adjusted so that a phase with increased lean operation follows a phase with at least two periods with mostly rich operation.  
     
     
         17 . A method according to  claim 1 , wherein before reaching an operating temperature of the catalyst the characteristic of the control signal deviates from the characteristic after surpassing the operating temperature.  
     
     
         18 . A method according to  claim 1 , wherein in a catalyst at almost operating temperature, the characteristic curve of the control signal has a sawtooth trend before reaching a stipulated operating temperature.  
     
     
         19 . A method according to  claim 1 , wherein the catalyst state and/or a state of the sensor upstream and/or downstream of the catalyst is determined from the control signal.  
     
     
         20 . A device for adjustment of a fuel/air ratio for an internal combustion engine with an associated catalyst, comprising: 
 exhaust composition sensors,    a control unit for generating a control signal to influence the fuel/air ratio as a function of output signals of at least one of the sensors, said control signal comprising a characteristic curve for switching back and forth between an operating state with oxygen excess and an operating state with oxygen deficiency of the catalyst, and    means for adjusting a form of a characteristic curve as a function of oxygen and/or NO x  addition and/or desorption in the catalyst.    
     
     
         21 . A device according to  claim 20 , wherein a sensor is arranged in the exhaust system of the internal combustion engine upstream and downstream of the catalyst.  
     
     
         22 . A device according to  claim 21 , wherein the sensor upstream of catalyst is a broadband lambda probe with a constant characteristic.  
     
     
         23 . A device according to  claim 22 , wherein the sensor upstream of the catalyst is a two-point lambda probe with a transfer characteristic.  
     
     
         24 . A device according to  claim 21 , wherein the sensor downstream of the catalyst is a two-point lambda probe with a transfer characteristic.  
     
     
         25 . A device according to  claim 21 , wherein the sensor downstream of the catalyst is a broadband lambda probe with a constant characteristic.  
     
     
         26 . A device according to  claim 20 , wherein the catalyst is a three-way catalyst.  
     
     
         27 . A device according to  claim 26 , wherein the catalyst has a noble metal content of less than 60 g/ft 3 , especially less than 40 g/ft 3 , preferably less than 30 g/ft 3 , optimally less than 20 g/ft 3 , ideally less than 10 g/ft 3 .  
     
     
         28 . A device according to  claim 20 , wherein the catalyst is an NO x  storage catalyst.  
     
     
         29 . A device according to  claim 28 , wherein the catalyst has a noble metal content of less than 80 g/ft 3 , especially less than 60 g/ft 3 .  
     
     
         30 . A device according to  claim 20 , wherein the internal combustion engine is a directly injected internal combustion engine capable of layered charging.