TRACK SYSTEMSSUPPLEMENT 03


Network Rail runs, maintains and develops Britain’s rail tracks, signalling, bridges, level crossings, viaducts and 17 key stations


engineers to get a better understanding of how to manage track. It is also being used by a number of agencies outside Network Rail as a useful design tool since it can easily compare the likely rail life and most appropriate design (curvature, cant, rail section) and the likely maintenance and rail replacement frequencies for new schemes. Computer simulations also allow us to


explore the parameters which have most influence on the wheel/rail interface, indicating which factors will have the biggest impact on reducing wheel/rail forces under different operating conditions. In summary, the factors which have the most influence can be categorised into those which are features of the vehicles, the track, or a combination of the two. It is now well understood that the vehicle suspension characteristics, and particularly the


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stiffness of the primary yaw suspension, which controls the ‘steering’ ability of the wheelsets in the bogie, has a profound affect on the forces generated in the contact patch. Vehicles with ‘soft’ yaw suspensions are better able to negotiate curves than vehicles with stiffer suspensions since it is easier for the wheelsets to move relative to the bogie frame, steering the vehicle round the curve. This reduces the wheel/rail forces, reducing the risk of RCF damage or wear to both the wheel and rail. However, a vehicle with a soft suspension, although being kinder to the track during curving, is more likely to experience instability (‘hunting’) at speed on straight track, which can also be damaging to the vehicle and track and can lead to significant discomfort for the passenger. There is clearly an engineering compromise to be made here to ensure that


vehicles are designed for the routes and duty cycles that they will operate, with the softest suspension possible whilst maintaining stability and ride: a true systems issue. For the design of new vehicles, this understanding has been used to influence the vehicle suspension straight off the drawing board; it can be very difficult to modify the suspension after the vehicle has been built, much better to get the suspension right in the initial specification. For this reason, Network Rail has been working closely with the Department for Transport and vehicle manufacturers to ensure that wheel/rail forces are an important consideration in the design of the new vehicles for the IEP, Thameslink and Crossrail projects. In the case of modifying existing vehicles,


Network Rail has also worked closely with manufacturers of rubber suspension


European Railway Review Volume 18, Issue 2, 2012


Photo Credit: www.networkrail.co.uk


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