The Development Of The Control Unit For CNG/Gasoline Bi-Fuel Vehicle

Because of low emissions and low fuel cost, Natural Gas had receivedconsiderable attention worldwide as alternative fuel. While the key technology wasowned by foreign suppliers. The native company can not provide highly costeffective control units. In this paper, a third generation Bi-fuel Control Unit whichhad much higher performance price ratio was developed.MC9S12XET256supplied by motorola was the controller. Bi-fuel ControlUnit devlopmented in this paper, in master-slave archtecture, was able to matchdeferent types engines with3to8cylinders. With the help of calibration software,the construction parameters and sensors parameters can be changed in CNG-ECU,according to vehicle matched.Closed-loop air/fuel ratio feedback control which mantances the air-fuel rationear stoichiometric, and Adaptive Learn Programming (ALP) were designed forthis system. This ALP adjusts for hardware variation, long term changes inoperating conditions, degradation in the engine or the system, and changes in fuelcomposition.A prominent feature for this Bi-fuel Control Unit was the simulative-EGO-singal module. In part load, engine operated on lean mixture and this module senta simulative EGO singal to gasoline ECU, preventing it detecting the EGO sensorfault.With the BootLoader stored in a special address, the CNG-ECU could beupdated by calibration interface without any disassembly. The fault diagnosis andupdating online functions made the maintenance and repairs greatly convenient.The codes was tested on an IC engine produced by Jianghuai Automobile Co.Ltd．Then a JETTA vehicle was converted. The road test showed that: the Bi-fuelautomobile has a good acceleration performance and idle steady. The switch fromgasoline to CNG and CNG to gasoline was smooth.