A review of the technical details reveals why metro operators in general and Moscow Metro in particular benefit from ZF’s new Metro transmission. In the case of conventional helical cut transmissions, forces are applied not only in the circumferential direction but also in the axial direction – with negative consequences: The forces put load on the bearings and reduce efficiency. In order to avoid this effect,
ZF uses two innovative tapered thrust washers for the E-Rail-SH 15 F. In simplified terms, these are rings that are attached to the left and right sides of the drive pinion and slide on an oil film at the output gear. This lateral guidance guarantees that no axial forces from the gearing take effect on the bearing and the housing – the basis of many other improvements for metro transmissions.
On this basis, the ZF engineers could design input and output shafts with cylindrical roller bearings instead of conventional tapered roller bearings. The former are setting-free and make installation especially easy for service personnel, for instance in case of general inspections. In addition, this design is largely resistant to varying outside temperatures. For this reason, it works perfectly even in regions where temperatures drop way below zero in winter.
The temperature inside the ZF metro transmission remains cool, as well: the bearings are installed in a nondistorted way and not subjected to axial loads; for this reason their temperature only amounts to two degrees Celsius above that of the oil sump. This also relieves the mounts on the whole and contributes to a longer product service life. In commercial vehicles, this technology is well established: ZF has been using it successfully in this field for about 20 years. The single-part housing of the E-Rail-SH 15 F is extremely torsion-resistant and equipped with an oil sump cover. Thanks to wear-free ZF labyrinth seals, its leak tightness is very reliable in all driving situations.
The version of the E-Rail-SH 15 F for Moscow’s metro has another special feature: ZF designed it as hollow shaft drive. Rail vehicle manufacturers can thus attach the transmission in a very easy way to the wheelset axle. Furthermore, it can be transported without the heavy wheelset axle, which significantly reduces the logistics efforts and the transport costs for all parties involved. Not only does this have a positive impact on the initial installation but also on all subsequent vehicle inspections and the service case.
ZF is firmly convinced that this newly developed bearing concept for use within the Metro transmission will become the bearing concept of choice for all EMU transmissions in the future. In addition, the new bearing concept is not only for metro transmissions but also for high-speed applications. In those situations the E-Rail-SH 15F transmission can help to significantly reduce the strain on bearings and housings – currently a very significant problem for transmissions used in high-speed trains.
In summary, ZF has created a product innovation with the E-Rail-SH 15 F which is characterized by a sustainably good cost/benefit ratio, and meets all other requirements of transport authorities in an optimum way.