Fuel cell cars will probably hit the road in series volumes only by 2015, but Röchling Automotive in Laives has been working since years on the first prototype models. For example, the Mercedes Benz F-Cell A-class fleet is equipped with containers of the South Tirol team. GM-Opel also is relying on the expert knowledge of the engineering center south of Bolzano regarding its fuel cell fleet which has been tested since a long time.

"Everybody always likes to visit us," says Ludwig Huber, chief of 150 engineers located on site. In the middle of the mountain scenery visitors are shown future technical solutions from single components up to complete systems for automotive applications.

Product manager Dr. Matteo Piazzi offers a wrap up of the current development: "Fuel cell cars cook only with water, too! A fuel cell power train needs more heat to be transferred via the cooling system than an up to date internal combustion engine powered by gasoline or diesel. This is why the new power train comprises a cooling circle as well and therefore also an expansion container. Thus our coolant expansion containers are a key component. They represent real high tech products with multi chamber system, several safety valves and safety caps as well as a ion filter. The chambers are assigned for the high and low temperature cycle."

The container is a system relevant component for flawless operation of a fuel cell, because temperature and humidity management is decisive for electric conductivity of the cells membrane. Based on this an electric current is generated within the membrane stack adding up to energy for the electric propulsion.

Separation of the aggregate state by container geometry

The fuel cell principle depends on a coolant without any conductivity. Therefore the ions must be filtered out of the fluid. This is achieved by a ion filter. It is directly accessible and exchangeable with a few touches. Against this backdrop it is enormously important that no particles come off from the containers inner surface, the opening sections and the assembly parts. The ion exchanger is placed in a way that it is passed by a maximum volume of the reflowing coolant.

To degas the reflowing coolant is one of the main tasks of the container. "What we are especially well-known for, that is the separation of gases and fluids within the smallest package and with the easiest approach", explains Piazzi. "No matter, if rain water separation at fresh air intake or at raw air intake for the engine, or just the separation of vapour and fluid within a coolant container.

Thus there are measurements by design to separate aggregate states. They enable a balance of fluid levels without bubbles. Furthermore a special outlet allows for gas probes for evaluation purposes.

Container flooding as a routine measurement

In order to avoid that any hydrogen escapes into the surrounding, the container is flooded with nitrogen before it is opened. Two openings are dedicated to this. “Because it can never be excluded that an inflammable gas mix accumulates in the upper chambers, the service manual demands a mandatory squeeze out of all the air from the cavities before the caps are opened”, describes Piazzi. "We call this a flooding. It is accomplished by a harmless gas injected with elevated pressure. This precaution ensures that no hydrogen can escape during service. All the caps are designed as safety closures."

Bursting pressure of up to 40 bar for hydrogen expansions

The high bursting pressure which was specified for the container is remarkable. A bursting pressure flap offers a regulation, just in case hydrogen is set on fire inside. If the regulation capacity of valves and flap is exceeded, predetermined breaking lines in the container wall absorb excessive energy in an advancing way. Thus the peak level of the burst noise is flattened literally. Absolute sound pressure is reduced considerably.

The high inner pressure called for a remarkable wall thickness. This meant a conflict with the maximum weight target and the request to keep the material transparent enough for recognizing the liquid level inside. The solution required the input of the whole inhouse resin competence.

Yet the job was also about precision mechanics: a safety valve regulates surplus pressure from a preset level, another control valve enables to let out still higher pressure. One of the overpressure valves is integrated into the refill cap.

Development focused on the simulation of the relief flows with CFD software, especially regarding the pressure loss and the air distribution in extreme situations. Underpressure can be compensated for within the container from a preset level as well.

An opening between the two chamber systems guarantees a balancing of the fluid even at the lowest water level. Further a mutual gas exchange was made possible for the two volumes above. At the same time heat exchange between both temperature levels is limited.

State of the art container technology for a new application

Operating temperatures from minus 25 degrees up to 80 degrees and ambient air temperatures from minus 40 degrees up to 100 degrees during parking correspond with usual requests for engine compartment containers. Other specifications are also met. Yet in the fuel cell context they have another meaning.

For example, the electric level indicator must not be disturbed by electromagnetic fields. This specification is easy to meet within combustion engine compartments. Nearby an electric powertrain it demanded additional measurements. Apart from this the level indicator as usual must not trigger false alerts when the car is parked inclined.

The construction details needed to accomplish this are day to day business for Röchling Automotive and Piazzi: “This new line of containers means for us that through all the change in vehicle construction we will be riding the curve also in future decades. Even pure battery electric cars require a cooling.” The company was already a world market leader for vehicle containers in 1986, when the South Tirol enterprise Seeber was acquired by Röchling.

The "Engineering Center Leifers" in the global manufacturing network

At the outskirts of the Brenner Pass there are over 6 million containers manufactured per year today, besides intake manifolds, air ducts, windshield cowls and media pipes. "These parts are developed here for Laives and 17 other Röchling Automotive sites, together with the regarding processes and tools. Our inhouse tool shop secures our leading edge. Even in China," Huber says. Röchling acquired in 2006 the shares of its Chinese joint venture partner and opened two locations as wholly owned subsidiaries in the empire of the sun.