Abstract
The hybrid buses the paper is concerned with, are the result of a spin-off from a research program developed at the University of Genova since 1987. The industrial product (Altrobus) became ready to market in 1994, and the vehicle started operating in regular service in 1996.
Later, feedback information from the field allowed for significant improvement in both reliability and energy-efficiency, and to a lesser extent driveability.
The energy chain consists of a DI diesel engine, an AC generator, a rectifier, a Pb-acid battery package, an inverter and an asyncronous AC motor.
The system can operate either in hybrid mode (diesel engine on) or electric mode (diesel engine off), hence it can be temporarily emission free (ZEO = zero emission operation).
After a brief survey of the drive-train main features, the control strategies will be described with a special concern for the diesel power on-off schedule. The optimal strategy must account for energy balance, battery life and the lowest emission: the latter being very close to the least fuel consumption condition.
Further considerations will be developed about the control of regenerative braking.
The reduced environmental impact of hybrids is compared to the potentials of other friendly vehicles, e.g. LPG, NG, trolley buses, etc. Unfortunately any means to improve the air quality in cities leads to extra costs: therefore an economic analysis is carried out, which determines the investment required by the different technologies, in order to reach an assigned level of emission decrease.