5 Questions to Paul Hofbauer, Product Manager Hydraulics

1. Mr Hofbauer, Liebherr-Transportation is applying electrohydraulic actuators from the aviation industry for railway use – why?

In aviation, our colleagues of the Liebherr-Aerospace branch have been on the market with electrohydraulic actuators for over 30 years. Weight plays a very important role here. The corresponding actuators are therefore very compact and lightweight. The great advantage of this is that both the hydraulic and the electric power are housed decentrally in the electrohydraulic actuator. Without these decentralised units, hydraulic lines previously had to be laid throughout the entire aircraft. Today, hydraulics are positioned in the actuator and controlled centrally. This makes it easy to replace the unit. We have been using this technology for railway applications since 2011.

2. Where exactly are the electrohydraulic actuators used in the railway sector?

Around 800 electrohydraulic actuators are used, for example, in the Italian high-speed train Frecciarossa (Zefiro). These enable active lateral damping and thus ensure greater travel comfort at high speeds.

Our actuators are also on board in Twindexx Swiss Express trains on the Basel-Lausanne route. This is where Bombardier’s roll compensation technology is used, enabling a scheduled travel time of less than 60 minutes on this route. With active control by the actuators as part of the roll compensation, curves can be driven through more quickly without passengers feeling uncomfortable or even sick.

3. With regards to accessibility: are actuators also used for lifting carriage bodies to align them to the platform level?

Yes, and our actuators are mainly used in North America. A directive there prescribes such a level control system.

Our hydraulic level actuators compensate for the loading condition of the train and thus lower the vehicle until the exit edge exactly matches the height of the platform. Our technology is used, for example, in urban railways and trams in Boston, Chicago, Cincinnati, Houston, Kansas and Toronto. However, this level control system is not a decentralised system: the actuators are connected to a central hydraulic pump unit.

4. Accessibility is now also mandatory in Europe. Are level control systems already being integrated into rail vehicles?

Not yet. Implementation will still take a while. But, of course, carriage manufacturers are thinking about solutions.

5. Some trains “screech” very loudly when driving through curves. Does Liebherr also have a solution for this at the ready?

Yes we do. Our active radius steering system (eCAS), which is currently under development, has the advantage that the wheel adjusts tangentially to the rail curve. This results in reduction of unwanted forces between wheel and rail and ultimately less wear. Simulations show that the lower friction between wheel and rail also reduces screeching when driving through curves. However, this has not yet been tested in practice. Up to now, the system has mainly been in demand because of the associated track protection.

One of our new projects is active yaw damping. This increases the traction of locomotives. Up to 17 kN more tensile force is possible with up to 10 kN less lateral forces between wheel and rail. This technology is particularly interesting for countries with winding railway lines. In this context, we were very pleased last year to receive an order from Siemens AG for the supply of active rotary damper systems for Vectron locomotives. With this order, our systems will be used as standard equipment in locomotives for the first time.