Ammonia storage control

Abstract

Various methods for controlling ammonia levels stored in a catalyst by controlling exhaust gas temperatures are provided. In one embodiment, a temperature of a catalyst in an internal combustion engine is determined. If the temperature of the catalyst exceeds a first threshold at which an ammonia capacity of the catalyst for the temperature is below a current stored ammonia level in the catalyst, a load of the engine is reduced including adjusting a torque output of a motor operatively coupled to the engine.

1 . A method for operating an internal combustion engine, comprising:
 controlling a load of the internal combustion engine based on an exhaust gas temperature of the engine;   wherein an energy conversion device drivingly coupled to the engine is configured to absorb power from the engine and output additional power to the engine,   wherein the load of the engine is reduced if a temperature of at least one catalyst of the engine exceeds a maximum permissible temperature, and   wherein the energy conversion device is operated as a selectable auxiliary drive to satisfy a requested additional power demand.   
     
     
         2 . The method of  claim 1 , wherein the internal combustion engine is deactivated if the temperature of the at least one catalyst exceeds the maximum permissible temperature, and
 wherein the energy conversion device is operated to satisfy the requested additional power demand.   
     
     
         3 . The method of  claim 2 , wherein the energy conversion device is operated to drive the internal combustion engine in order to pump fresh air through the at least one catalyst. 
     
     
         4 . The method of  claim 1 , wherein the internal combustion engine is deactivated if the temperature of the at least one catalyst exceeds the maximum permissible temperature, and
 wherein the energy conversion device is operated to drive a secondary air pump in order to pump fresh air through the at least one catalyst.   
     
     
         5 . The method of  claim 1 , wherein the maximum permissible temperature is between 350° C. and 450° C. 
     
     
         6 . The method of  claim 1 , wherein the load of the internal combustion engine is increased in order to raise the exhaust gas temperature and hence the temperature of the at least one catalyst; and
 wherein the energy conversion device is operated as a selectable generator in order to absorb excess power provided by the engine.   
     
     
         7 . The method of  claim 1 , wherein the load of the internal combustion engine is increased if the temperature of the at least one catalyst falls below a minimum permissible temperature; and
 wherein the minimum permissible temperature is between 120° C. and 200° C.   
     
     
         8 . The method of  claim 1 , wherein the internal combustion engine is operated in a medium load range, the energy conversion device operated as a selectable auxiliary drive to satisfy the requested additional power demand if a high power is demanded; and
 wherein the energy conversion device operated as a selectable generator to absorb excess power provided by the engine if a low power is demanded.   
     
     
         9 . The method of  claim 8 , wherein the medium load range includes loads between 30% and 70% of a maximum load of the internal combustion engine at a given engine speed. 
     
     
         10 . The method of  claim 1 , wherein ammonia is used as a reductant; and
 wherein the internal combustion engine is operated such that a sufficiently large store of ammonia is built up in the at least one catalyst for restarting to reduce nitrogen oxides in a warm-up phase.   
     
     
         11 . A method, comprising:
 adjusting an amount of supplemental motor torque in response to an amount of ammonia stored relative to a storage capacity of an SCR catalyst coupled to an internal combustion engine.   
     
     
         12 . The method of  claim 11 , wherein the amount of supplemental motor torque is adjusted if a temperature of the SCR catalyst exceeds a first threshold at which the storage capacity of the catalyst for the temperature is below the amount of ammonia stored, while reducing a load of the engine. 
     
     
         13 . The method of  claim 12 , wherein the amount of supplemental motor torque is adjusted to supply additional torque if a driver-demanded torque is undershot after reducing the load of the engine; and
 wherein the amount of supplemental motor torque is adjusted to reduce torque if the driver-demanded torque is overshot after reducing the load of the engine.   
     
     
         14 . The method of  claim 12 , wherein reducing the load of the engine includes deactivating the engine. 
     
     
         15 . The method of  claim 12 , wherein reducing the load of the engine includes enleaning an air/fuel mixture. 
     
     
         16 . The method of  claim 11 , wherein the amount of supplemental motor torque is adjusted if a temperature of the SCR catalyst falls below a second threshold at which urea substantially evaporates, thereby increasing a load of the engine. 
     
     
         17 . The method of  claim 16 , wherein the amount of supplemental motor torque is adjusted to supply additional torque if a driver-demanded torque is undershot after increasing the load of the engine; and
 wherein the amount of supplemental motor torque is adjusted to reduce torque if a driver-demanded torque is overshot after increasing the load of the engine.   
     
     
         18 . The method of  claim 16 , further comprising, if the load of the engine is in a low region, and the amount of ammonia stored is below the storage capacity of the catalyst, injecting urea upstream of the catalyst. 
     
     
         19 . A method, comprising:
 reducing a load of an internal combustion engine in proportion to an amount of ammonia stored relative to a storage capacity of an SCR catalyst; while adjusting an amount of supplemental motor torque, based on exhaust temperature.   
     
     
         20 . The method of  claim 19 , wherein the load of the engine is reduced in proportion to the stored ammonia level in the catalyst such that stored ammonia level is maintained below the ammonia capacity.