Abstract
Abstract
The driveline in on-highway vehicle is defined not just by the engine and axle system but most importantly, also by the transmission selected. The dominant transmission currently used in city buses is the automatic powershift transmission. In coaches, it is the automated transmissions, such as the ZF-ASTronic. The latter however is increasingly replacing manual transmissions which are still the most prevalent types of transmission on this market. The requirements placed on the transmission system are undergoing tremendous change: The main challenges that transmission development has to face up to are the further development of combustion engines with ever increasingly torque levels, but also rising coolant temperatures, and ever more stringent emissions’ and fuel economy requirements for the entire vehicle. Questions relating to economic viability, comfort, and safety have been and - of course – are still at the center of attention when it comes to “standard” requirements. The wishes of end customers, i.e. vehicle operators, are mostly but not in all regards identical with the requirements of vehicle manufacturers. This makes the creation of a generally valid recommendation for the selection of a transmission system much more difficult. This paper will firstly provide an overall illustration and the details of the origin of these requirements as well as the importance attached to them by vehicle manufacturers and vehicle operators respectively. Subsequently follows an overview of the types of transmissions presently available (manual transmissions, automated transmissions, powershift transmissions) and other interesting designs which may appear in the future (dual clutch transmissions, continuously variable transmissions [mechanical, electrical etc.]). To what extent do today’s transmissions and those of the future satisfy the relevant requirements? An assessment, differentiated for various applications, is presented in detail, trends and their meanings are evaluated and linked to recommendations for currently valid transmission selection criteria. A look into the future provides an insight into the extent to which alternative vehicle concepts and transmission systems are going to influence current developments.