INTRO: English Welsh & Scottish Railway is due to begin operations this month with four-piece Swing Motion¨ bogies using a common secondary suspension for both axles. The aim is to reduce purchase and maintenance costs while meeting European ride quality standards

BYLINE: Steve Becker

Executive Vice President, NACO Technology

In its search for dependable bogies with a low purchase price and reduced life-cycle costs, Britain’s principal rail freight operator English Welsh & Scottish Railway has decided to adopt the Swing Motion bogie from NACO of the USA.

The first bogies were shipped in June, to be fitted to 310 steel coil wagons being built for EWS at Thrall Europa’s new plant in York. The first of these was handed over on July 27 (below), and is expected to enter service shortly.

Later this month, EWS will decide whether to order up to 1 000 further sets of Swing Motion bogies for retrofitting to its existing wagons. The final decision awaits a periodic inspection of the prototype bogies undergoing revenue service trials under two steel carriers operating in northeast England.

EWS expects the Swing Motion design to produce substantial savings in maintenance costs - to the extent that retrofitting will be cheaper than overhauling its existing bogies. The company’s intention is to retrofit vehicles as and when their bogies fall due for a full overhaul, starting with the heavily-worked steel carrier fleet.

Design development

The four-piece Swing Motion bogie was originally developed for North American applications, and to date 47 different variants have been put into service under more than 100 wagon types around the world. Adaptation to EWS requirements was carried out by NACO’s design and research development centre using Advanced Vehicle Dynamics¨ technology.

In contrast to the single axle per spring group primary suspension that prevails in Europe, the near-universal standard for North American bogies is for both axles to share a coil spring secondary suspension. Unlike the basic three-piece design, where the transverse bolster rests on the side frames directly through the secondary suspension, the Swing Motion bogie incorporates a separate transom. The swing bolster rests on two pairs of triple coil springs, which are carried by the lower transom. Each coil spring is nested to provide a two rate suspension to meet loaded and tare ride requirements.

A patented swing hanger design decouples the wheelsets from the wagon body, thus abating the damaging forces between the wheel/rail interface and the wagon. This gives increased lateral stability at speeds up to 176 km/h for some US applications.The swing hanger configuration also reduces wheel and track wear, improving fuel efficiency and reducing stress and fatigue on the wagon structure.

The pivotal issue in developing the EWS design has been engineering a balance between cost and ride quality. The Y25 primary suspension bogies in use throughout Europe meet International Union of Railways standards in terms of ride quality and track impact, but they are expensive. Our challenge has been to produce a bogie that is not only substantially less expensive to buy and maintain, but also meets stringent British ride quality standards.

The Swing Motion design for EWS has undergone months of testing by Railtrack, with empty and loaded vehicles measured in operation for lateral and vertical forces on the wagon body against the standard Freight Acceptance Curve. Tests have been conducted on jointed and continuous welded rail. The wagons met all performance criteria at controlled speeds during the first phase of testing, and the bogie was subsequently cleared for operation at speeds up to 125 km/h.

The new Thrall Europa steel carrier has also passed its ride tests as part of the Railtrack vehicle acceptance process. According to EWS, the Swing Motion bogie configuration produced significantly lower than predicted lateral track forces. Vertical ride results were described as ’comfortably within’ Railtrack’s criteria in loaded running and on the specification for the tare condition.

Lower costs, higher axleloads

The Swing Motion design will reduce life-cycle costs, and through its lower weight will also allow higher payloads. The lower life-cycle costs should afford EWS significant savings over the Y25. NACO expects to supply a minimum of several hundred bogies per year over the next few years.

Fatigue problems with some existing European bogie designs can require extensive reconditioning at frequent intervals. The Swing Motion bogie has proved in North American service that it can provide 10 years or 2·4million km of service without scheduled maintenance, in contrast to an average of four years for the Y25 primary suspension unit.

The first tests for EWS were conducted on steel carrier wagons with a payload of 102 tonnes, but the Swing Motion design allows axleloads up to 35·7 tonnes. EWS, infrastructure owner Railtrack, Thrall Europa and NACO are currently at the early stages of a test programme for higher axleloads in Britain, but in early 1998 Swedish State Railways completed testing with NACO’s Axle Motion II bogie. This has allowed an increase in axleloads to 30 tonnes with lower track forces than 22·5 and 25 tonne UIC bogies. This will boost payloads by up to 50% - in some cases without the need to reinforce the infrastructure.

However, reduced purchase and life-cycle costs, rather than an immediate requirement for lower track forces or higher speeds and axleloads, have been the driving force behind the decision by EWS to adopt North American bogie technology in Britain.

Designed for Europe

NACO has studied the complex dynamics of wagons in motion and has applied new technologies in designing bogies from the track up to meet the particular needs of European railways. In contrast to the fabricated steel bogies common in Europe such as the Y25 with its welded frame, the swing motion bogie has a four-piece cast steel frame. Computer-aided design and precision manufacturing give the Swing Motion design a longer fatigue life.

The rugged secondary suspension, specifically designed for a long service life, has larger friction surface areas with low wear rates that are shared by two axles. This is measurably different from the suspension of the Y25, which requires high levels of maintenance. Due to its design and manufacture, we believe that the NACO Swing Motion suspension will outlast any bogie design in use throughout Europe today. o

CAPTION: Computer-aided design was used extensively in the adaptation of the Swing Motion bogie to suit European conditions

CAPTION: The first Thrall Europa 102 tonne steel carrier with Swing Motion bogies for EWS has already passed its Railtrack ride quality trials