Triple peaks
General drive technology
Ansgar Silies
Key Account Manager, KTR Germany
Mai 2018 • Up top the air’s thin – this holds true in both a metaphorical and factual sense. For example atop Germany’s highest mountain, the Zugspitze, the lack of oxygen helps one lose weight. Alpine air slims people down without any physical effort – thanks to the increased basal metabolic rate and a smaller appetite at high altitudes.
But first of all one has to reach such heights. Some half million visitors manage this each year, for example with cogwheel train and glacier cable car, and as of 21 December 2017 with cable car! That’s when the new Zugspitze Cable Car commenced operation to Germany’s highest peak additionally and, in doing so, picking up three world records.
Two large-capacity cabins – both with glass floors –transport up to 580 people an hour to the mountain’s summit, providing the visitors a breathtaking mountain and valley view and foresight during the ten-minutes journey. On their way visitors pass a single steel support pylon for the aerial tramway, the world’s tallest at 127 metres, and also experience the largest height difference of 1,945 metres within one section as well as 3,213 metres of unsupported cable – the longest anywhere. Both world firsts. Shortly before the destination it goes uphill quite steeply: At this point the cable car overcomes a maximum incline of 104.7 per cent.
Twin cables are used to suspend each cabin of the new Zugspitze cable car. And each of the four cables is 4.6 km long, has a diameter of 72 mm and weighs 153 tons.
To pull the suspension ropes up the mountain, we had to develop a special rope pull system. Logistics up the mountain was a key aspect with this project anyhow.
Markus Reichmuth
Project manager Seilbahn Zugspitze, Doppelmayr/Garaventa-Group
1,800 kW twin drive in the valley station
A total of six years planning and construction have been invested in this shuttle service which gets into gear in the new base station. The cabins are driven via a twin drive having a rated power of 1,800 kW. The drives are operating simultaneously transmitting each half of the total power required to a double-groove drive pulley which is connected with the cabin via a traction cable. Every drive pulley is provided with a service and safety brake each affecting separated flange-mounted brake disks.
Great expertise with the selection of cable car drives
The powerful and highly available spur gears were manufactured by SEW-EURODRIVE, each having a rated torque of 240,000 Nm. SEW-EURODRIVE’s Swiss national subsidiary, Alfred Imhof AG, was in charge of project planning. Project Engineer Peter Baumgartner who has also selected the couplings accounted for the selection of the gearboxes. In addition to typical basic data such as torque and speed parameters like low temperatures which are also decisive with the selection of the lubricant had to be considered.
The twin drive system is structured redundantly so that the cable car can be driven by one drive only, too. Technical safety has an extremly high level in this case.
Peter Baumgartner
Product engineer industrial gear units, Alfred Imhof AG/SEW-Switzerland
Motor side: „XXL“ ROTEX with flywheel
The main drive of the Zugspitze cable car comprises a ROTEX jaw coupling which is suitable for rated torques up to 19,200 Nm and an operating speed of 1,495 rpm. A flywheel having a diameter of 900 mm and a thickness of 235 mm enhances smooth running in the drive system and correspondingly the travelling convenience from the passenger point of view.
Pulley side: Failsafe pin & bush coupling
The connection between gearbox and pulley is realized by a torsionally flexible failsafe REVOLEX pin & bush coupling. Taper steel pins with elastomer rings ensure torque transmission between the two hub halves. Here both misalignment is compensated and a smooth, i. e. torsionally flexible start-up of the drive and consequently cabin is achieved. In case of maintenance the elastomer rings including the pins can be dismounted when installed.
The REVOLEX coupling in the drive of the Zugspitze cable car transmits rated torques up to 300,000 Nm with an operating speed of 59.3 rpm. The shaft-hub-connection is realized by a KTR external clamping set type 620. The pin & bush coupling has an outside diameter of 1.20 metres and a weight of 3.6 tons. Since the main drive train is uncoupled with emergency operation and the auxiliary drive is engaged, it has a shiftable design.
Auxiliary drive: Shiftable gear coupling
The couplings on the opposite side of the pulley which connect the auxiliary drive with the overall drive logically are shiftable design as well. These electrohydraulic drives are only engaged when the main drives fail and the cabins have to be run into the stations in control. In contrast to the main drive elasticity is not a feature of convenience with start-up of the drive, especially since the hydraulics provide for elasticity. That is why a double-cardanic all-steel gear coupling type GEARex is installed in this drive train.
The hubs having a crowned spline transmit torques up to 300,000 Nm positively while compensating for axial, radial and angular shaft displacements reliably. As measured by its performance data, this coupling type compact and easy to assemble because of its ability for axial plug-in. In the Zugspitze cable car’s auxiliary drive it runs at a lower operating speed of 8.4 rpm at the maximum.
All couplings in the drive of the Zugspitze cable car are supplied by KTR. They make sure that the power generated by the motors and gearboxes is transmitted to the two cable sheaves. But passengers will hardly notice this due to the breathtaking panoramic views such as the picturesque Eibsee lake, the Alpspitze mountain or the Waxenstein mountain range. The journey won’t be disturbed by coarse judders, more likely it will be a smooth floating ride to lofty thin-aired heights.
