Harry Hondius reports on Siemens' progress with plans to reinforce the low-floor Combino trams as announced in 2005. A new hydraulic control system offers an elegant option that is being adopted in Basel

OVER THE PAST five years, Siemens engineers have been working on a programme to reinforce the bolted aluminium bodyshells of the Combino low-floor tram family, following the emergence of torsion fatigue problems in 2002. By mid-2005 a detailed strategy had emerged to modify a total of 454 cars (RG 10.05 p615).

Between 1998 and 2006, Siemens delivered 114 Basic and 310 Advanced Combino cars, plus 36 NF10 and 15 NF8 cars for Rheinbahn in D sseldorf. In total, this required the modification of 2 418 bodyshell modules.

The process of strengthening the Combino Advanced cars is in full swing, with 125 vehicles completed by the end of 2006: 56 from Amsterdam, 15 from Bern, 27 from Erfurt, 10 from Freiburg, 5 from Nordhausen and 12 from Poznan. At present around 10 or 12 cars are being rebuilt per month. All the cars still on order in 2005 have now been delivered, the last batches for Erfurt, Nordhausen and Freiburg incorporating the modifications from new.

The carbodies are being dealt with at Uerdingen and the trucks at Maribor the Melbourne cars are being modifed in Australia at the city's Preston depot. Fortunately for the engineers, the Combino Advanced cars are largely identical in technical specifications. The main difference is that the Amsterdam, Poznan and Ulm cars have 2 400 mm wide bodies while the Bern, Freiburg, Nordhausen and Erfurt vehicles are only 2 300 mm. The Melbourne cars are different again with a width of 2 650 mm. All cars are having their roof articulations changed.

The main differences between the Advanced cars and the Basic version are:

  • a standardised front end to an altered design
  • a reinforced and cost-optimised underframe, especially at the front end to make it less susceptible to shunting damage and to permit automated welding
  • 100 mm higher doors
  • Reinforced roof panels to support higher roof loads, notably air-conditioning equipment
  • An integrated seat module above the trucks
  • enlargement of the standard side pillars from 80 to 120 mm.

Basic cars are more complex

The situation with the Combino Basic cars appears to be more complicated than originally anticipated, demanding more intrusive reinforcement, which has caused a delay compared to the original plan. Complicating matters was the fact that the Combino design was still evolving when Basic cars were built, and thus they are not identical. For example, the upper end sills and corner pillars were reinforced. The need to treat many Basic models required far more calculations to achieve a written proof that the changes would deliver the desired operational resistance.

The 42 m long Basel cars were always special, because of their longer modules and air-conditioning, plus the requirement to operate around 11 8 m radius curves. To get a full picture of the loads on the various elements a Basel Combino was submitted to extensive load testing on its own network. The roof articulations and the connection from the trucks to the body were optimised to minimise the loads. The resulting measurements were compared with those for an unmodified car.

Figs 1 and 2 show the extra changes to the bogie/front module and saloon module, compared with the original proposal (RG 10.05 p617, Fig 7). The most important of these are the changes to the corner pillars and upper end sills and to the articulation end sills (below).

The first modified Basic for Basel - car 310 - was handed over to BVB on December 22 2006 (below right). Following handover it was fitted with strain gauges and subjected to a comprehensive stress measuring programme, like that undertaken with Amsterdam car 2091 in the summer of 2005. The Basel car re-entered revenue service in March.

The Basic rectification programme envisages that 27 cars for Basel and 16 for Potsdam will be reinforced in Uerdingen, along with the 51 Rheinbahn NF cars. Because of capacity and time constraints, the other cars will be treated in Wien, including the 12 Hiroshima cars which will be transported to Austria. The European Combino rectification programme is now expected to be completed by the end of 2008.

Hydraulic coupling tested

The arrangement of the roof articulations for the modified Basel car (in order) is now: pivoting bearing, galloping bearing with damper, pivoting bearing, galloping bearing with damper, pivoting bearing and rolling/pivoting bearing with damper. However, Siemens has also developed a passive hydraulic rolling control system1. When this is applied, all the pivoting bearings become rolling/pivoting bearings and a hydraulic cylinder replaces the dampers in the galloping and rolling pivoting bearings.

These hydraulic cylinders couple the rolling bearings on both sides of a saloon module. The operating principle is simple: the two hydraulic cylinders mounted in a closed circuit linking the two ends of a saloon module will compensate for any rolling movement of the adjacent powered modules, so that there is only one position for the saloon module (Fig 3). This will enable the cars to ride over track distortions without subjecting the modules to high forces.

The lateral forces that are the determinant factors for the torsion stress, are reduced by a factor of 10 compared to the un-modified version. The hydraulic system is equipped with an oil reservoir and a stop valve that has to be closed if a car is to be lifted after a derailment.

A prototype of this system was fitted to Basel car 328 in September 2005, and has been tested in passenger service since October 7 of that year. In the first tests the saloon modules were deliberately displaced into an extreme oblique position, but had regained their normal position after the car had run for about 10 m.

Clearance tests were made, the car was lifted and re-gauged, and no problems were discovered. BVB has been very enthusiastic about the improvement in the riding qualities, especially the softer running through curves, and the elimination of the 'clicking' heard in the unmodified car bodies. BVB has decided to fit all 28 of its Basic cars with this system, and other Combino operators have expressed interest.

It looks as if Siemens and its clients have now entered into the final phase of what was the Combino drama. It caused many operators political as well as operational headaches but might in the end provide them with a simple and sturdy vehicle, well suited to their needs.

  • Fig 1 shows the extra rectifications measures for the Combino Basic driving modules, compared to the Advanced model. From above: cantrail stiffener, connector at window pillar and cant rail, new upper end sills, new corner pillar, stiffener at equipment box, articulation end sill reinforcement. Both ends of each driving module ends must be modified Diagram: Siemens
  • Fig 2 shows the additional rectification measures required on the Combino Basic saloon modules, comparison to the Advanced model. From above: cant rail reinforcement, new corner pillar, sidewall reinforcements, connector at corner pillar and sole bar, end port of sole bar, connector at door pillar and sole bar Diagram: Siemens
  • Fig 3: Vertical view of the roof-mounted hydraulic rolling control system. Top: track inclined to the left. Centre: level track. Bottom: track inclined to the right Diagram: Siemens
  • The first completely-rectified Combino Basic for Basel, car 310, was returned to the city in December 2006 Photo: BVB
  • Door side corner pillars for the Combino Basic
  • New end portal for the Combino Basic, showing the connection of the new pillars Photos: Siemens
  • A rolling/pivoting bearing is used with the a hydraulic cylinder instead of a hydraulic damper as has been fitted to the refurbished series cars Diagram: Siemens
  • The complete arrangement of the rolling/pivoting bearing and cylinder, showing the oil reservoir and stop valve Photo: Siemens
  • Looking as new, reconstructed Combino Advanced cars Poznan 609, Amsterdam 2012 and Bern 764 stand outside the Siemens plant in Uerdingen