System and Methods for Skip Fire Engine with a Lean NOx Trap

Abstract

Systems and methods for skip fire spark ignition engine operation with a lean NOx trap after-treatment are provided. This system includes engine control circuitry capable of fueling and firing subsets of the engine's cylinders. Other cylinders are not provided fuel and are not fired (i.e. “skip fired”). The system includes an exhaust manifold for channeling the exhaust from at least some cylinders through a multistage catalytic converter. This may include a standard two-way or three-way catalytic converter. From the catalytic converter the exhaust may be channeled through a lean NOx trap. The lean NOx trap is able to chemically absorb the NOx emissions for regeneration according to a regeneration protocol. Lean NOx traps may include a substrate, an absorption material (also referred to as a ‘sorbent’) and a catalyst. The regeneration protocol may include monitoring NOx emissions downstream from the lean NOx trap, and comparing them against either a threshold or a lean NOx trap saturation model. Once the NOx emissions reach the threshold, or deviate from the model, a regeneration cycle may be performed.

What is claimed is: 
     
         1 . A method for operating a spark ignition internal combustion engine, wherein the internal combustion engine includes a plurality of cylinders, each of the plurality of cylinders being capable of operating in a succession of combustion cycles, the method comprising:
 substantially regulating the control of fuel to and firing an activated subset of the plurality of cylinders according to a firing pattern;   substantially deactivating the fueling and firing of a deactivated subset of the plurality of cylinders;   channeling exhaust emissions from at least one of the cylinders of the deactivated subset of the plurality of cylinders and at least one of the activated subset of the plurality of cylinders through a lean NOx trap, wherein the lean NOx trap chemically absorbs NOx emissions within the exhaust emissions; and   regenerating the lean NOx trap in accordance to an NOx regeneration protocol.   
     
     
         2 . The method for operating the spark ignition internal combustion engine, as recited in  claim 1  wherein the NOx regeneration protocol includes:
 monitoring NOx emissions downstream from the lean NOx trap; 
 comparing the monitored NOx emissions to a threshold; and 
 regenerating the lean NOx trap when the monitored NOx emissions are higher than the threshold. 
 
     
     
         3 . The method for operating the spark ignition internal combustion engine, as recited in  claim 1  wherein the NOx regeneration protocol includes regenerating the lean NOx trap periodically. 
     
     
         4 . The method for operating the spark ignition internal combustion engine, as recited in  claim 1  wherein the NOx regeneration protocol includes regenerating the lean NOx trap in accordance with a lean NOx trap saturation model. 
     
     
         5 . The method for operating the spark ignition internal combustion engine, as recited in  claim 1  wherein the NOx regeneration protocol includes:
 monitoring NOx emissions downstream from the lean NOx trap; 
 comparing the monitored NOx emissions to a lean NOx trap saturation model; and 
 regenerating the lean NOx trap according to the comparison of the lean NOx trap saturation model and the monitored NOx emissions. 
 
     
     
         6 . The method for operating the spark ignition internal combustion engine, as recited in  claim 1 , wherein the regeneration of the lean NOx trap includes injecting a rich fuel mixture into at least one of the activated subset of firing cylinders. 
     
     
         7 . The method for operating the spark ignition internal combustion engine, as recited in  claim 1 , wherein the regeneration of the lean NOx trap includes introduction of a reducing agent to the lean NOx trap. 
     
     
         8 . The method for operating the spark ignition internal combustion engine, as recited in  claim 2 f, wherein the reducing agent includes at least one of fuel, hydrogen gas, and a urea solution. 
     
     
         9 . The method for operating the spark ignition internal combustion engine, as recited in  claim 1 , wherein regeneration of the lean NOx trap occurs a minimum of thirty seconds after the previous regeneration cycle. 
     
     
         10 . The method for operating the spark ignition internal combustion engine, as recited in  claim 1 , wherein the spark ignition internal combustion engine is one of a port injection engine, a direct injection engine and a carbureted engine. 
     
     
         11 . The method for operating the spark ignition internal combustion engine as recited in  claim 1 , wherein at least one of the plurality of cylinders includes valves that can be independently controlled. 
     
     
         12 . The method for operating the spark ignition internal combustion engine, as recited in  claim 1 , wherein the lean NOx trap includes a zeolite. 
     
     
         13 . The method for operating the spark ignition internal combustion engine, as recited in  claim 1 , wherein the lean NOx trap includes an alkali. 
     
     
         14 . The method for operating the spark ignition internal combustion engine, as recited in  claim 1 , wherein the lean NOx trap includes an alkaline earth material. 
     
     
         15 . The method for operating the spark ignition internal combustion engine, as recited in  claim 14 , wherein the lean NOx trap includes barium salt. 
     
     
         16 . The method for operating the spark ignition internal combustion engine, as recited in  claim 1 , wherein the lean NOx trap includes at least one of a platinum and a rhodium based catalyst. 
     
     
         17 . The method for operating the spark ignition internal combustion engine, as recited in  claim 14 , wherein the chemical absorption of the NOx emissions includes oxidation of the alkaline earth material. 
     
     
         18 . The method for operating the spark ignition internal combustion engine, as recited in  claim 1 , further comprising channeling exhaust emissions from at least one of the cylinders of the deactivated subset of the plurality of cylinders through a multistage catalytic converter prior to channeling the exhaust emissions through the lean NOx trap. 
     
     
         19 . The method for operating the spark ignition internal combustion engine, as recited in  claim 18 , wherein the multistage catalytic converter is proximally located to the lean NOx trap. 
     
     
         20 . The method for operating the spark ignition internal combustion engine, as recited in  claim 19 , wherein there is an absence of artificial cooling between the multistage catalytic converter and the lean NOx trap. 
     
     
         21 . The method for operating the spark ignition internal combustion engine, as recited in  claim 20 , wherein artificial cooling includes any of cooling loops, refrigeration and fluid cooling. 
     
     
         22 . The method for operating the spark ignition internal combustion engine, as recited in  claim 1 , wherein the deactivated subset of the plurality of cylinders add substantially non-combusted air into the exhaust emissions. 
     
     
         23 . The method for operating the spark ignition internal combustion engine, as recited in  claim 1 , wherein the firing pattern is generated by an engine control unit using an adaptive predictive controller. 
     
     
         24 . The method for operating the spark ignition internal combustion engine, as recited in  claim 23 , wherein the adaptive predictive controller includes a sigma delta controller. 
     
     
         25 . The method for operating the spark ignition internal combustion engine, as recited in  claim 24 , wherein the adaptive predictive controller includes feedback indicative of at least one of requested and actual working cycle firings. 
     
     
         26 . The method for operating the spark ignition internal combustion engine, as recited in  claim 1 , wherein an engine control unit determines the ratio of air and fuel provided to the activated subset of cylinders. 
     
     
         27 . The method for operating the spark ignition internal combustion engine, as recited in  claim 26 , wherein the ratio of air and fuel provided to the activated subset of cylinders varies between lean and rich of stoichiometry. 
     
     
         28 . The method for operating the spark ignition internal combustion engine, as recited in  claim 27 , wherein the duration the activated subset of cylinders is provided one of lean and rich fuel to air ratios is substantially longer than typical engine operation. 
     
     
         29 . The method for operating the spark ignition internal combustion engine, as recited in  claim 28 , wherein at least one oxygen sensor of the internal combustion engine is overridden. 
     
     
         30 . A method for operating an internal combustion engine, wherein the internal combustion engine includes a plurality of cylinders, each of the plurality of cylinders being capable of operating in a succession of combustion cycles, the method comprising:
 firing a subset of the plurality of cylinders during each combustion cycle, wherein at least one of the plurality of cylinders is skip fired, an wherein uncombusted air is passed through the at least one skip fired cylinder into the exhaust emissions;   channeling exhaust emissions from at least one of the cylinders through a lean NOx trap, wherein the lean NOx trap chemically absorbs NOx emissions within the exhaust emissions; and   regenerating the lean NOx trap in accordance to an NOx regeneration protocol.