Development of capacitor hybrid system for urban buses

The authors have developed a capacitor hybrid vehicle equipped with a newly developed capacitor system and a miller cycle CNG engine for low floor urban buses. The CNG engine drives a generator at over 40% thermal efficiency. The newly developed capacitor system, since it has high energy and power density, is able to regenerate almost all the braking energy of a 14-ton bus at over 90% charging efficiency. The internal resistance of the capacitor system is minimized by the capacitor itself and a new capacitor connection. Furthermore, the voltage dispersion of the capacitor cells is minimized by the capacitor charging control system. The fuel economy was improved by 166% compared with the CNG low-floor bus and the vehicle efficiency reached over 45% in the M15 mode test.