Active Control in Railway Vehicles

The most notable progress which has taken place in the design and development of railway rolling stock over the last few decades is the increasing integration of electronics and control in rail vehicles which used to be purely mechanical systems [1,2]. The aim of this paper is to survey the applications of active control and mechatronics in railway vehicles, providing an overview of active control technologies which have recently been brought to the level of revenue service, of ongoing research topics still under development that have already proven their potential through experimental demonstration, and of more "blue sky" oriented research which is likely to impact upon rail vehicles on a longer timescale. In particular, this review will cover the topics of active primary and secondary suspensions and active pantograph control. From the implementation point of view, it is noticeable that the introduction of active control remains fairly restricted: tilting of course is now an accepted, relatively mature technology with widespread use [3], but there is only one operational example of any other type of active secondary suspension [4]. Furthermore, although active primary suspension technology is offered by one manufacturer, at present this has not been incorporated into operational trains. With respect to active pantographs, few experimental versions exist (e.g. [5]), but again none have been applied in revenue operation. History shows, however, that there are inexorable trends toward better performance requirements, and it is likely that sooner or later various types of active technology will become standard within the railway industry: much as has already happened for aircraft and is happening for automobiles. It is not obvious in which way railways are so different from these other transportation modes that they should not follow the lead of these other industries. There are also significant economic and political pressures to reduce the cost of railways: not only the price of tickets for the passengers, but also the subsidies from national governments. However, the biggest cost reductions are likely to arise from active solutions that affect both sides of the vehicle/track interface, in which case, there are difficulties with realising such innovations when many train operations are financially separated from the infrastructure. In the longer term, consideration could be given to new configurations, in particular taking advantage of mechanical simplifications afforded by the use of control technology, and essentially trading off mechanical for electronic complexity in the true spirit of a mechatronic approach.