After five years of development, the prototype Korean Tilting Train is now under construction. Taking to the tracks at the end of this year, it promises a significant enhancement in service quality on Korail's conventional network

Seo Sung-Il
Director, Conventional Rail Engineering Corps, Korea Railroad Research Institute

NOW TAKING shape in the Rotem plant at Changwon in South Korea is a prototype trainset that offers the prospect of major improvements to conventional passenger services on the country's rail network.

Due to roll out at the end of this year and start test running in early 2007, the six-car TTX tilting trainset is the result of more than five years of research and development.

As around 70% of South Korea's land area is occupied by hills and mountains, most routes on the national rail network have a high proportion of curves, which constrain train speeds. This is being overcome on the principal Seoul - Taejong - Taegu - Pusan corridor by the construction of a new high speed line. But a policy of balanced national development means that citizens in other regions need improved rail services where new line construction cannot be justified. Hence the drive to develop a train that can improve speeds on the conventional lines.

Since April 1 2004 KTX trainsets derived from French TGV technology have been running at up to 300 km/h on the first section of the high speed line. They have now been joined by the prototype Korean High Speed Train 350X, which has achieved its target speed of 350 km/h on test and is expected to enter commercial service in 2009. Developed by Korean researchers and the domestic rolling stock industry, KHST350X has already completed 130000 km of reliability test running.

But the fastest trains on the conventional network are the Saemaul diesel units which have now been running for 20 years at a maximum of 140 km/h. We needed to develop a fast electric train to plug the huge speed gap between Saemaul and the KTX. Thus the Korean Tilting Train TTX is designed to operate at speeds up to 200 km/h.

The TTX (Tilting Train eXpress) has been under development since 2001 by KRRI and a consortium of Korean manufacturers. Because of growing concern over air pollution and noise emissions, we decided to move from the diesel-powered Saemaul trainsets to an electric train, which has a reduced impact on the environment.

Work is currently underway on electrifying a number of main lines across South Korea where the TTX will operate. Work has already been completed on the route from Taegu to Pusan, which is being used by KTX trains pending completion of the second phase of the high speed line. Wiring is now in progress on the Joongang Line from Seoul to Andong and the Kyungbu Line between Seoul and Taegu.

The prototype trainset is formed of four motor cars and two trailers. All vehicles are 23·6m long, and the maximum axleload is 14 tonnes. There are eight motor bogies, with 16 axles powered by 250 kW motors giving a total continuous rating of 4 000 kW. Performance simulations suggest that TTX will be able to cut journey times on principal conventional lines by around 20%.

Composite bodyshell

TTX has been designed for light weight, enhanced reliability and safety, easy maintenance, and a high quality of passenger service.

Running faster on conventional routes will require improved track maintenance. To minimise the impact of increased track forces when running through curves at higher speeds, and reduce the risk of overturning, the tilting train must be as light as possible, with a low centre of gravity to ensure stability in curves.

To meet these requirements, we developed the concept of a hybrid carbody structure. The upper part of the bodyshell is made of a lightweight composite material and the underframe is fabricated from stainless steel to give strength and ensure a low centre of gravity. Hybrid bodyshells have been tried in other countries, but only on a small scale. Composite bodyshells have been built for EMUs, LRVs and high speed trains. But to date we do not believe that anyone has built an entire carbody from composites.

The upper body of the TTX is composed of carbon fibre composite skins with a honeycomb core. It has been fabricated at high pressure and high temperature in a large-scale autoclave. The use of this composite honeycomb plate has reduced the overall weight of the bodyshell by around 30% compared to existing trains.

Because of the innovative nature of this composite bodyshell, extensive testing was needed to to verify the safety of the design. Fatigue load tests were carried out on an actual body on our large-scale test facility, together with the usual static load tests.

Other tests included fire testing using a simulated incendiary scenario, together with vibration and sound transmission tests. Overall, the results of this testing programme confirmed the validity and safety of the hybrid composite bodyshell design.

The interior has been designed to be luxurious and comfortable, with rotating seats that face the direction of travel. The luggage racks have been replaced by enclosed bins with latching doors, to prevent luggage from falling out when the train is tilting. Amongst the other features being provided for the passenger is a small LCD monitor on each seat for on-train entertainment, and wireless internet connections are available in each vehicle. Around 20% of the interior space is devoted to passenger facilities.

Tilting technology

The TTX carbody is supported on a tilting bolster, which is connected to the bogie frame through a linkage. Electro-mechanical actuators on the bogie can tilt the body on the bolster by up to 8í. Gyroscopic sensors and accelerometers detect each curve in conjunction with GPS to verify the train location.

When a curve is detected, the Tilt Train Processor triggers the actuators, which move the links and tilt the carbody. The tilting angle is calculated on the basis of train speed, lateral acceleration, curve radius and cant deficiency. The TTP issues the tilting commands to each car with a time delay, so as to tilt the carbodies sequentially as each vehicle enters the curve.

A self-steering mechanism on the bogie mitigates the lateral forces exerted by the wheels when running faster through curves. The running safety of the bogie system has been verified by roller rig tests at simulated speeds up to 240 km/h.

As the train tilts through a curve, the pantograph must tilt in the opposite direction in order to maintain contact with the overhead line. The pantograph is mounted on a sledge on the roof, which is supported by rollers and guide rails. Tilting commands for the pantograph are issued by the TTP simultaneously with those for the tilting bolster.

To minimise weight at roof level, the sledge assembly has been designed to be as light as possible. The single arm of the pantograph is fabricated from an aluminum tube to reduce its weight. The span of the contact pan has been made wider than usual to insure that it does not lose contact with the catenary during tilting.

TTX is powered by asynchronous three-phase traction motors, with an IGBT converter-inverter pack feeding each pair of motors. These are cooled by natural convection. The converters use pulse width modulation, and the inverters control the motors using VVVF.

Regenerative braking is fitted, and this is the primary braking mode at speeds above 50 km/h. Wheel-mounted brake discs are fitted to save space in the motor bogies, but conventional axle-mounted discs are used on the trailer bogies. The braking control unit blends regenerative and air braking to ensure optimum performance at all points on the speed curve. The air compressor module has been designed as a single compact unit to save space and permit easy maintenance.

On-board ATP

The standard ATS cab signalling equipment used on conventional lines in South Korea is not suitable for operation at speeds above 160 km/h. To permit operation at the planned 200 km/h, TTX is being equipped with onboard ATP. Because of the short timescale available for development, lineside ATP equipment being installed on the test route between Gwangju and Mokpo uses European standard components, in the form of ETCS Level 1 with Eurobalises.

An integrated Train Monitoring System links all onboard devices, monitoring their performance and feeding a display on the driver's desk. The TMS also monitors the tilt control system and advises the driver of the responses required to deal with any equipment failures.

To verify the performance of TTX, the prototype train is being fitted with a comprehensive instrumentation and measurement system. Sensors on each device will transmit additional information back to the main processor unit for further analysis. Separate monitors are being installed in one of the passenger saloons for use by the testing and commissioning team.

We expect to start testing the prototype TTX for performance and reliability on the conventional network from the beginning of 2007. Once these tests have been completed, the train will be put into commercial service to assess the passenger reaction.

Following these trials, we expect Korail to decide in early 2009 whether to place orders for a series build of TTX. This would see the trains entering service in 2010.

  • CAPTION: Artist's impression of the Korean Tilting Train, which is due to start test running next year
  • CAPTION: Fatigue load testing was carried out to confirm the structural validity of the hybrid composite bodyshell
  • CAPTION: The lightweight pantograph is carried on a roof-mounted sledge which compensates for body tilt when passing through curves
  • CAPTION: The TTX motor bogie has two 250 kW motors. Wheel-mounted brake discs free up space inside the bogie for the tilt bolster and the electro-mechanical tilt actuators