Exhaust gas recirculation flow control for reducing emissions with variable displacement internal combustion engines

Abstract

Managing firing fraction transitions of a variable displacement internal combustion engines by (a) avoiding transport delays in an Exhaust Gas Recirculation (EGR) feed by starting movement of an EGR valve position after a decision to transition to a new firing fraction has been made, but prior to the start of the transition and (b) adjusting the EGR valve as needed during the transition so as to maintain an EGR fraction within a predetermined range during the transition. By performing both (a) and (b), spikes of nitrous oxide (NO x ) and/or hydrocarbon emissions are reduced or altogether eliminated during the transition.

What is claimed is: 
     
         1 . A controller for directing operation of an engine in a vehicle, the controller configured to:
 operate the engine at a first firing fraction during a first engine cycle;   generate a command to operate the engine at a second firing fraction that is different than the first firing fraction;   ascertain a delay for starting the transition of operation of the engine from the first firing fraction to the second firing fraction, wherein the delay is ascertained based at least partially from an operational parameter of the engine;   ascertain when the delay has expired; and   start the transition of the operation of the engine from the first firing fraction to the second firing fraction after the delay has expired.   
     
     
         2 . The controller as recited in  claim 1 , wherein the operational parameter is a resetting of an accumulator to a select value and the delay is ascertained by a time required to wait for resetting the accumulator to the select value. 
     
     
         3 . The controller of  claim 1 , wherein the operational parameter is completion of a current engine cycle, and the delay is ascertained from a time required to complete the current engine cycle. 
     
     
         4 . The controller of  claim 1 , wherein the operational parameter is a turbo charger configuration, and the ascertained delay is an estimated amount of time needed to complete adjustment of the turbo charger configuration ahead of the transition of the engine from the first firing fraction to the second firing fraction. 
     
     
         5 . The controller of  claim 1 , wherein the operational parameter is a firing of a select cylinder positioned closer to an Exhaust Gas Recirculation (EGR) system relative to at least one other cylinder of the engine and the delay is ascertained from a time required for waiting for the select cylinder to be next fired. 
     
     
         6 . The controller of  claim 1 , wherein the operational parameter is a predetermined fire-skip pattern for a select cylinder of the engine and the delay is based on coordinating a timing needed to implement the predetermined fire-skip pattern for the one cylinder. 
     
     
         7 . The controller of  claim 1 , wherein the operational parameter is a predetermined trigger event and the delay is based on waiting for the trigger event to occur before starting the transition from the first firing fraction to the second firing fraction. 
     
     
         8 . The controller of  claim 1 , further configured to operate the engine in a variable displacement mode where a first group of one or more cylinders are continually fired and a second group of one or more cylinders are continually skipped when operating at the first firing fraction. 
     
     
         9 . The controller of  claim 1 , further configured to operate the engine in a skip fire mode where at least one cylinder is successively fired, skipped and either fired or skipped over three successive working cycles when operating at the first firing fraction respectively. 
     
     
         10 . A method for controlling operation of an engine in a vehicle comprising:
 ascertaining a delay, based at least partially on an operational parameter of the engine, for starting a transition of operation of the engine from a first firing fraction to a second firing fraction; and   starting the transition of the operation of the engine from the first firing fraction to the second firing fraction after the delay has expired.   
     
     
         11 . The method as recited in  claim 10 , wherein the operational parameter is a resetting of an accumulator to a select value and the delay is ascertained by a time required to wait for resetting the accumulator to the select value. 
     
     
         12 . The method as recited in  claim 10 , further comprising operating the engine in a skip-fire mode such that at least one cylinder is fired, skipped and either fired or skipped over successive working cycles while the engine is operating at the first firing fraction. 
     
     
         13 . The method of  claim 10 , wherein the operational parameter is completion of a current engine cycle and the delay is ascertained from a time required to complete the current engine cycle. 
     
     
         14 . The method of  claim 10 , wherein the operational parameter is a turbo charger configuration, and the ascertained delay is an estimated amount of time needed to complete adjustment of the turbo charger configuration ahead of the transition of the engine from the first firing fraction to the second firing fraction. 
     
     
         15 . The method of  claim 10 , wherein the operational parameter is a firing of a select cylinder positioned closer to an Exhaust Gas Recirculation (EGR) system relative to at least one other cylinder of the engine and the delay is ascertained from a time required for waiting for the select cylinder to be next fired. 
     
     
         16 . The method of  claim 10 , wherein the operational parameter is a predetermined trigger event, and the delay is based on waiting for the trigger event to occur before starting the transition from the first firing fraction to the second firing fraction. 
     
     
         17 . The method of  claim 10 , further comprising operating the engine in a variable displacement mode where a first group of one or more cylinders are continually fired and a second group of one or more cylinders are continually skipped when the engine is operating at the first firing fraction.