Abstract
Keywords - Serial Hybrid, Low Floor Bus Axle, Efficiency Simulation, Vehicle Architecture, Liquid Cooled Asynchronous Machine
Introducing hybrid solutions is an important approach to reduce fuel consumption and improve environmental compatibility - for passenger cars as well as for commercial vehicles. For city busses there are designs traced with parallel hybrid configuration as well as with serial hybrid configuration. This paper presents the stage of development of a low-floor bus drive axle for serial hybrid systems, which features integrated liquid cooled asynchronous motors. The axle is designed for use in the hybrid-option of a city bus. The paper discusses the general advantages and possibilities of the serial hybrid drive - especially regarding articulated vehicles - and deals with the special challenges of the axle design and the compatibility between standard bus and hybrid option.
Regarding the general advantages of serial configurations, simulations of fuel consumption are touched. The high impact of application cycles on prediction results is presented. Focus is given to the questions of vehicle design architecture. It can be shown that the components in a serial system can be arranged in a very flexible way avoiding e. g. problems with weight distribution or traction.
The design features of the new axle are covered in the second part. Starting from a predecessor design it is explained, how it was possible to meet the narrow installation space in a low floor bus. The communality of major components with the proven standard axle is shown. Specific design problems are the portal offset in a high-ratio gear reduction and the integration of the electric motor. The former has been solved with an innovative set of spur gears within a ring gear, which provides a space saving power split at the same time with the offset. The latter required a very sophisticated layout of the motor, which features special internal forced air ventilation and an external cooling jacket. These details are discussed.