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This paper discusses whether it is possible to improve the motor efficiency by a two-speed transmission in an electric bus, and if so, to what extent. Based on the China Bus Urban Cycle, an 8-meter electric bus was studied via simulation in Matlab/Simulink. The comparison of motor efficiency between two different configurations was made: direct drive and drive through a two-speed transmission. In the first part of the simulation, the speed ratios of the two-speed transmission were chosen as 1.5 and 3.5. The motor efficiency was improved by 1.22% for driving and 1.66% for generation. To find out the maximum improvement and corresponding optimal speed ratio combination, scanning experiment of the lower ratio and upper ratio was conducted in the second part. As much as 1.66% improvement of driving efficiency and 2.20% of regenerating efficiency was achieved.

This paper studies a control algorithm for fuel cell/battery city buses. The output power of the fuel cell is controlled by a D.C. converter, and the output ports of the converter and the battery are connected in parallel to supply power for the electric motor. One way to prolong service life is to have the fuel cell system to deliver a steady-state power. However, because of fluctuations in the bus voltage and uncertainness in the D.C. converter, the output power of the fuel cell system changes drastically. A closed-loop control algorithm is necessary to eliminate the errors between the output and target power of the fuel cell system. The algorithm is composed of two parts, the feed forward one and the feedback one. Influences of the bus voltage and D.C. efficiency are compensated automatically in the feedback algorithm by using a PI algorithm. The stability and robustness of the algorithm is analyzed.

In-cylinder pressure sensor, which provides the means for precise combustion control to achieve improved fuel economy, lower emissions, higher comfort, additional diagnostic functions etc., is becoming a necessity in future diesel engines, especially for chemical-kinetics dominated PCCI (Premixed Charge Compression Ignition) or LTC (Low Temperature Combustion) engines. In this paper, new control strategy is investigated to utilize in-cylinder pressure information into engine start process, in order to guarantee the success of engine start and in the meantime prevent penalty of fuel economy or pollutant emissions due to excessive fuel injection. An engine start acceleration model is established to analyze the engine start process. “In-cylinder Combustion Analysis Tool” (i-CAT), is used to acquire and process the in-cylinder pressure data and deliver the combustion indices to ECU (Engine Control Unit). Feedback control is accomplished in ECU based on this information.