AFR Control System Using TWC Outlet Oxygen Sensor

Abstract

The utilisation of the oxygen storage capacity of TWC is recently focused on for the improvement of emission purification and the purification of an engine exhaust gas is achieved fairly high level. However, the control system is seemed to be complicated to use such ability. For the simple utilisation of this ability, a new air fuel ratio control system and algorithm was investigated. The fuel injection mass was modulated periodically and the air excess ratio was detected at the TWC outlet by an oxygen sensor. As the output signal of an oxygen sensor was switching type, the signal value was filtered by a moving average method for translation to an analog value and the moving average value was used for the periodic modulation control as the control value. Furthermore, the two feed forward control system were equipped for fast response and stability of the fuel control. This simple control system was operated at transient state in many driving conditions, and compared with other control systems. The proposed control system can cut the emissions of NOx and THC concurrently and the reduced amount were larger than other control system.