System and method for determining a NOx storage capacity of a catalytic device

Abstract

In an apparatus having an internal combustion engine, a method of operating the engine including operating the engine at a first non-stoichiometric relative air/fuel ratio for a first duration; operating the engine at a second non-stoichiometric relative air/fuel ratio for a second duration, wherein the second relative air/fuel ratio is on an opposite side of a stoichiometric relative air/fuel ratio as the first relative air/fuel ratio, and wherein the second duration is of sufficient length to allow at least one of one of a substantial saturation of oxygen storage sites in the catalytic device and a substantial regeneration of oxygen storage sites in the catalytic device; and operating the engine at a third non-stoichiometric relative air/fuel ratio for a third duration, wherein the third relative air/fuel ratio is on a same side of the stoichiometric relative air/fuel ratio as the second relative air/fuel ratio and is further from the stoichiometric relative air/fuel ratio than the second relative air/fuel ratio.

1 . In an apparatus having an internal combustion engine, a catalytic device for treating emissions from the engine, an upstream oxygen sensor positioned upstream of the catalytic device, a downstream oxygen sensor positioned downstream of the catalytic device, and a controller configured to measure an oxygen storage capacity of the catalytic device from a difference between a signal received from the upstream oxygen sensor and a signal received from the downstream oxygen sensor, a method of operating the engine, comprising: 
 operating the engine at a first non-stoichiometric relative air/fuel ratio for a first duration;    operating the engine at a second non-stoichiometric relative air/fuel ratio for a second duration, wherein the second non-stoichiometric relative air/fuel ratio is on an opposite side of a stoichiometric relative air/fuel ratio as the first non-stoichiometric relative air/fuel ratio, and wherein the second duration is of sufficient length to allow at least one of one of a substantial saturation of oxygen storage sites in the catalytic device and a substantial regeneration of oxygen storage sites in the catalytic device; and    operating the engine at a third non-stoichiometric relative air/fuel ratio for a third duration, wherein the third non-stoichiometric relative air/fuel ratio is on a same side of the stoichiometric relative air/fuel ratio as the second non-stoichiometric relative air/fuel ratio and is further from the stoichiometric relative air/fuel ratio than the second non-stoichiometric relative air/fuel ratio.    
   
   
       2 . The method of  claim 1 , wherein the first non-stoichiometric relative air/fuel ratio is rich, and wherein the second and third non-stoichiometric relative air/fuel ratios are lean.  
   
   
       3 . The method of  claim 1 , wherein the second non-stoichiometric relative air/fuel ratio is approximately 1.03, and wherein the third non-stoichiometric relative air/fuel ratio is greater than approximately 1.2.  
   
   
       4 . The method of  claim 1 , further comprising determining a difference between a signal received from the upstream oxygen sensor while operating the engine at the second non-stoichiometric relative air/fuel ratio and a signal received from the downstream oxygen sensor while operating the engine at the second non-stoichiometric relative air/fuel ratio.  
   
   
       5 . The method of  claim 1 , further comprising integrating a difference between an output from the upstream oxygen sensor and an output from the downstream oxygen sensor while operating the engine at the second non-stoichiometric relative air/fuel ratio.  
   
   
       6 . The method of  claim 5 , wherein the first non-stoichiometric relative air/fuel ratio is rich, and wherein the second and third non-stoichiometric relative air/fuel ratios are lean, further comprising setting the output from the downstream oxygen sensor to be no more rich than the output from the upstream oxygen sensor for a period of at least between a starting of integrating the difference between the outputs from the upstream and downstream oxygen sensors and a detecting of a lean exhaust mixture at the upstream oxygen sensor.  
   
   
       7 . The method of  claim 5 , further comprising determining a NO x  storage capacity of the catalytic device from the difference between the outputs from the upstream and downstream oxygen sensors.  
   
   
       8 . The method of  claim 5 , further comprising adjusting a temperature of the catalytic device to at least one of a diagnostic temperature and a diagnostic temperature range for integrating the difference between the outputs from the upstream oxygen sensor and the downstream oxygen sensor.  
   
   
       9 . The method of  claim 8 , wherein the diagnostic temperature is equal to or above a temperature of approximately 400 degrees Celsius.  
   
   
       10 . The method of  claim 9 , wherein the diagnostic temperature is within a range of approximately 400-700 degrees Celsius.  
   
   
       11 . The method of  claim 1 , wherein the catalytic device is a NO x  trap.  
   
   
       12 . In an apparatus having an internal combustion engine, a catalytic device, an upstream oxygen sensor positioned upstream of the catalytic device, a downstream oxygen sensor positioned downstream of the catalytic device, and a controller configured to measure an oxygen storage capacity of the catalytic device from a difference between a signal from the upstream oxygen sensor and a signal from the downstream oxygen sensor after a rich-to-lean relative air/fuel ratio transition, a method of operating the engine, comprising: 
 operating the engine for a first duration at a rich relative air/fuel ratio to remove stored NO x  from the catalytic device;    operating the engine for a second duration at a first lean relative air/fuel ratio, wherein the second duration has a duration sufficient to allow saturation of the catalytic device with oxygen; and    operating the engine for a third duration at a second lean relative air/fuel ratio, wherein the first lean relative air/fuel ratio is more lean than the second lean relative air/fuel ratio.    
   
   
       13 . The method of  claim 12 , wherein the first lean relative air/fuel ratio is approximately 15, and wherein the second lean relative air/fuel ratio is approximately 17-100.  
   
   
       14 . The method of  claim 12 , further comprising determining a difference between a signal received from the upstream oxygen sensor while operating the engine at the first lean relative air/fuel ratio and a signal received from the downstream oxygen sensor while operating the engine at the first lean relative air/fuel ratio.  
   
   
       15 . The method of  claim 12 , further comprising integrating a difference between an output from the upstream oxygen sensor and an output from the downstream oxygen sensor while operating the engine at the first lean relative air/fuel ratio.  
   
   
       16 . The method of  claim 15 , further comprising setting the output from the downstream oxygen sensor to be no more rich than the output from the upstream oxygen sensor for a period of at least between a starting of integrating the difference between the outputs from the upstream and downstream oxygen sensors and a detecting of a lean exhaust mixture at the upstream oxygen sensor.  
   
   
       17 . The method of  claim 15 , further comprising determining a NO x  storage capacity of the catalytic device from the difference between the outputs from the upstream and downstream oxygen sensors.  
   
   
       18 . The method of  claim 15 , further comprising adjusting a temperature of the catalytic device to at least one of a diagnostic temperature and a diagnostic temperature range for integrating the difference between the outputs from the upstream oxygen sensor and the downstream oxygen sensor.  
   
   
       19 . The method of  claim 18 , wherein the diagnostic temperature is equal to or above approximately 400 degrees Celsius.  
   
   
       20 . The method of  claim 19 , wherein the diagnostic temperature is within a range of approximately 400-700 degrees Celsius.  
   
   
       21 . The method of  claim 12 , wherein the catalytic device is a NO x  trap.  
   
   
       22 . An apparatus, comprising: 
 an internal combustion engine;    a catalytic device for treating emissions from the engine;    an upstream oxygen sensor positioned upstream of the catalytic device and downstream of the engine in a direction of emissions flow;    a downstream oxygen sensor positioned downstream of the catalytic device; and    a controller configured to enhance a sensitivity of a measurement of a difference between a signal received from the upstream oxygen sensor and a signal received from the downstream oxygen sensor by operating the engine at a first non-stoichiometric relative air/fuel ratio for a first duration; operating the engine at a second non-stoichiometric relative air/fuel ratio for a second duration, wherein the second non-stoichiometric relative air/fuel ratio is on an opposite side of a stoichiometric relative air/fuel ratio as the first non-stoichiometric relative air/fuel ratio, and wherein the second duration is of sufficient length to allow at least one of one of a substantial saturation of oxygen storage sites in the catalytic device and a substantial regeneration of oxygen storage sites in the catalytic device; and operating the engine at a third non-stoichiometric relative air/fuel ratio for a third duration, wherein the third non-stoichiometric relative air/fuel ratio is on a same side of the stoichiometric relative air/fuel ratio as the second non-stoichiometric relative air/fuel ratio and is further from the stoichiometric relative air/fuel ratio than the second non-stoichiometric relative air/fuel ratio.    
   
   
       23 . The apparatus of  claim 22 , wherein the first non-stoichiometric relative air/fuel ratio is rich, and wherein the second and third non-stoichiometric relative air/fuel ratios are lean.  
   
   
       24 . The apparatus of  claim 22 , wherein the second non-stoichiometric relative air/fuel ratio is approximately 15, and wherein the third non-stoichiometric relative air/fuel ratio is approximately 17-100.  
   
   
       25 . The apparatus of  claim 22 , wherein the controller is further configured to determine a difference detected between a signal received from the upstream oxygen sensor while operating the engine at the second non-stoichiometric relative air/fuel ratio and a signal received from the downstream oxygen sensor while operating the engine at the second non-stoichiometric relative air/fuel ratio.  
   
   
       26 . The apparatus of  claim 22 , wherein the controller is further configured to integrate a difference between an output from the upstream oxygen sensor and an output from the downstream oxygen sensor while operating the engine at the second non-stoichiometric relative air/fuel ratio.  
   
   
       27 . The apparatus of  claim 26 , wherein the first non-stoichiometric relative air/fuel ratio is rich and the second and third non-stoichiometric relative air/fuel ratios are lean, and wherein the controller is further configured to set the output from the downstream oxygen sensor to be no more rich than the output from the upstream oxygen sensor for a period of at least between a starting of integrating the difference between the outputs from the upstream and downstream oxygen sensors and a detecting of a lean exhaust mixture at the upstream oxygen sensor.  
   
   
       28 . The apparatus of  claim 26 , wherein the controller is further configured to determine a NO x  storage capacity of the catalytic device from the integrated difference between the outputs from the upstream and downstream oxygen sensors.  
   
   
       29 . The apparatus of  claim 26 , wherein the controller is further configured to adjust a temperature of the catalytic device to at least one of a diagnostic temperature and a diagnostic temperature range for integrating the difference between the outputs from the upstream oxygen sensor and the downstream oxygen sensor.  
   
   
       30 . The apparatus of  claim 29 , wherein the diagnostic temperature is equal to or above approximately 400 degrees Celsius.  
   
   
       31 . The apparatus of  claim 30 , wherein the diagnostic temperature is within a range of approximately 400-700 degrees Celsius.  
   
   
       32 . The apparatus of  claim 22 , wherein the catalytic device is a NO x  trap.