Method for load transient control between lean and stoichiometric combustion modes of direct-injection engines with controlled auto-ignition combustion
View Patent ↗A method is provided for control of a direct-injection engine operated with controlled auto-ignition (HCCI) during load transient operations between modes of lean combustion low load (HCCI/Lean) and stiochiometric combustion medium load (HCCI/Stoich.). The method includes 1) operating the engine at steady state, within a homogeneous charge compression-ignition (HCCI) load range, with fuel-air-exhaust gas mixtures at predetermined conditions, for each speed and load, and controlling the engine during changes of operating mode between one to another of the HCCI/Stoich. medium load mode and the HCCI/Lean lower load mode by synchronizing change rates of predetermined controlled inputs to the current engine fueling change rate.
1. Method for control of a direct-injection engine operated with controlled auto-ignition during load transient operations between modes of lean combustion low load (HCCI/Lean) and stiochiometric combustion medium load (HCCI/Stoich.), the method comprising:
operating the engine at steady state, within a homogeneous charge compression-ignition (HCCI) load range, with fuel-air-exhaust gas mixtures at predetermined conditions, for each speed and load, of fueling mass flow rate (fueling rate), injection timing (FI), spark timing (SI), throttle position, exhaust gas recirculation (EGR) valve setting, and exhaust recompression obtained by negative valve overlap (NVO) between closing of the exhaust valves and opening of the intake valves in each cylinder; and
controlling the engine during changes of operating mode between one to an other of HCCI/Stoich. medium load mode and HCCI/Lean lower load mode by synchronizing change rates of predetermined controlled inputs to the current engine fueling change rate, the predetermined controlled inputs including at least three of FI, SI, throttle position, EGR valve setting and NVO.
2. Method as in claim 1 and adjusting at least one of FI, SI, NVO, throttle and EGR valve position to control cylinder maximum rate of pressure rise, partial burns and misfires, the method including:
measuring engine intake oxygen percentage and exhaust air-fuel ratio; and
adjusting at least one of FI, SI, NVO, throttle and EGR valve position so that measured intake oxygen percentage and exhaust air-fuel ratio closely follow predetermined values during transition between modes of lean combustion low load (HCCI/Lean) and stoichiometric combustion medium load (HCCI/Stoich.).
3. Method as in claim 1 wherein the engine inputs are synchronized by a feed forward control that maintains predetermined relationships between instantaneous fueling rate values and corresponding values of related engine inputs during load transient operations.
4. Method as in claim 3 wherein said predetermined relationships are provided by lookup tables accessible by a computer control system.
5. Method as in claim 3 wherein a feedback control adjusts the feed forward control based on measured values of engine performance to minimize errors in the controlled output values and more closely align the output values to the predetermined relationships.
6. Method as in claim 5 wherein said predetermined relationships are provided by lookup tables accessible by a computer control system.