Turbo transmission (Voith)

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Turbo transmissions are hydrodynamic multi-circuit transmissions for rail vehicles driven by internal combustion engines. The first turbo transmission was developed by Voith in Heidenheim an der Brenz in 1932 . Since then, the turbo transmissions have been adapted to the steadily growing requirements of diesel traction and today, after the dominant electrical power transmission, they occupy the most important position worldwide.

In turbo transmissions, the engine power is converted into wheel power hydrodynamically via a torque converter and turbo coupling using kinetic or dynamic energy from a liquid mass. This is deflected in blade channels at high flow speeds and low pressure. They differ from the hydrostatic gears , in which the energy conversion also takes place via a liquid, but at high static pressure and low flow speeds according to the displacement principle.

principle

Turbo transmissions are hydrodynamic multi-circuit transmissions in which the power is transmitted hydrodynamically in the entire operating range according to the Föttinger principle . Torque converters , turbo couplings and, optionally, hydrodynamic brakes are combined into multi-circuit transmissions. What they all have in common is their use in rail vehicles powered by diesel engines .

history

The first turbo transmission from 1932 was very simple. It contained a torque converter for the starting range and a turbo coupling for the operating range, which were arranged on a common rotor shaft. The most important feature of the new turbo transmission was the principle of filling and emptying the hydrodynamic circuits adopted by the Föttinger marine transmissions. It offered wear-free starting, wear-free gear changes without interruption of tractive power, freewheel effect by emptying the circuits and a high level of efficiency thanks to the turbo coupling in the operating range.

In contrast to Föttinger , Voith used low-viscosity mineral oil as the operating fluid instead of water for the turbo gearboxes from the very beginning. In the thirties, numerous improvements were made to the turbo transmission: installation of the high gear, compact design and adaptability to various engines, automatic gear shifting and heat dissipation via heat exchangers .

In the early 1960s, the hydrodynamic brake was added as a third circuit type to the converter and clutch . All of the design improvements made over the decades had the aim of increasing the permissible transmission capacity with the same construction effort without jeopardizing the high reliability of the transmission.

Transmission with two circuits for railcars

A small T 211 r turbo transmission was developed in 1969 as an alternative to the hydromechanical bus transmissions for the lower power range of diesel multiple units from 200 to 300 hp. Like the first turbo transmission, it has the torque converter / clutch rotor combination, but with high gear and significantly improved efficiency in the converter area. It also contains the turning part and can be equipped with a hydrodynamic brake if necessary. The circuit diameters are only slightly larger at 346 mm for the converter and 305 mm for the clutch. The rotor speed is significantly higher at 4,170 min-1 due to the high gear. The reinforcements and improvements that have been made since then show what reserves are hidden in the hydrodynamic part of the T 211 r. They only concern the mechanical part (gears, bearings and shafts) and the transmission control. In contrast, the profile diameters of the converter, clutch and brake remained unchanged. The circumferential speeds of the circuits increased in accordance with the increase in the permissible transmission input power from 205 kW to 350 kW. The rotor speed reaches almost 5000 min-1 at 350 kW, the peripheral speed at the maximum speed of the vehicle (empty converter!) Of the freely rotating converter turbine at the outlet is 74 m / s. The filling pump has been reinforced to ensure sufficient heat dissipation from the converter even at 350 kW. At this output it delivers 3.5 l / s of oil through the heat exchanger in traction mode, 9 l / s in the short-circuited circuit when braking. The brake rotor then acts as a circulation pump at the same time. Externally visible changes compared to the predecessor type T 211 re.3 with 320 kW maximum input power are the electronic control unit directly attached to the gearbox and the enlarged ventilation filter.

Three-circuit transmission for railcars

For the new Quick Multiple units with tilting technology VT 611 / 612 of the Deutsche Bahn is 1995 a completely redesigned transmission of the type converter clutch coupling with integrated hydrodynamic brake T 312 bre designed for 650 kW of power. In order to achieve a short overall length, two runners are driven via a high-speed trio, similar to the turbo reversing gear. The electronic transmission control is attached to the transmission. The two reversing cylinders are hydraulically operated so that there is no need to provide compressed air for the transmission. Following the same concept, the T 212 bre for 460 kW followed five years later, which, in contrast to the larger gearbox, can be flange-mounted directly to the engine. This is made possible by a short motor-gear unit for underfloor installation in high-speed railcars with a top speed of 200 km / h. It took over the size of the circuits from the T 211 r. The T 212 br has the advantage that from 50% of the top speed you can drive in efficient clutch areas. This is a great advantage, especially for diesel multiple units used in fast regional traffic , which leads to lower fuel consumption with the same operating performance.

Two-converter transmissions for locomotives

For powerful mainline locomotives, a new L 620 reU2 two-converter gearbox with a starting converter of 525 mm and a starting converter of 434 mm profile diameter was designed in 1999, the concept of which is based on the proven L 520 rzU2 for 1,400 kW output. In accordance with the higher input power of 2,700 kW, all parts of the transmission must be enlarged and strengthened. In the case of the secondary gearbox, two gear wheels are arranged on the countershaft instead of the intermediate gear in the L 520 rzU2. The output speed level can thereby be adapted to the respective requirements of the locomotive via the output gear pair. The output shaft has a large bearing base of 550 mm. Overall, the new large gearbox shows the enormous power concentration that hydrodynamic power transmission offers. With a power-to-weight ratio of 2.06 kg / kW, the new L 620 reU2 has an unprecedented value for locomotive transmissions. The comparable L 520 rzU2 has a power-to-weight ratio of 2.4 kg / kW. The optionally attachable hydrodynamic brake KB 385 is newly developed for this gearbox. The Kiel locomotive manufacturer Vossloh installs these transmissions in its large B'B 'mainline locomotives G1700 and G2000 . The LS 640 reU2 turbo split gearbox has two rotors from the L 620 reU2 for the separate drive of the two bogies of a six-axle diesel locomotive and is being installed for the first time in the Voith Maxima locomotive with an engine output of 3,600 kW.

Performance selection Choice of turbo transmission

The engine power to be installed and the choice of a suitable gearbox are determined by the operating program of the rail vehicle. These are the operating conditions with trailer loads for diesel locomotives and seating capacity for diesel multiple units , the topography of the routes to be traveled and, above all, the climatic conditions for non-European operations. These criteria are contained in the technical tender conditions and determine the points:

  1. Top speed
  2. Acceleration of the vehicle formation in the starting area, taking into account the friction weight of the driven wheelsets.
  3. When using diesel multiple units in suburban traffic, certain acceleration values ​​must be adhered to in consideration of the dominant operation of electric multiple units in order to avoid traffic jams on the route.
  4. Compliance with certain minimum speeds on longer inclines.
  5. Dynamic braking, especially at high speeds, but also when driving on long downhill stretches, the use of a dynamic brake is economical or necessary.

Maximum speed, vehicle mass, acceleration and gradients determine the engine power to be installed. In addition, there is the power requirement for the auxiliary services, i.e. air conditioning , cooling system , brake compressor and, in the case of locomotives, possibly a central energy supply for air conditioning and heating of the passenger coaches. This means that the diesel engine can be selected, large V-engines for locomotives , 6-cylinder underfloor engines for locomotives or compact 12-cylinder V-engines from the commercial vehicle sector. Underfloor gears combined with the engine as a power pack with a low installation height are the preferred solution for modern diesel railcars.

The further development of the hydrodynamic torque converter

In turbo transmissions, the torque converter forms the heart, which over the decades has been adapted to the traction requirements of diesel traction vehicles. The aim of the development work is not only the best possible degree of efficiency, but also a high level of start-up conversion without any loss of completeness in the case of the start-up converters and as constant a power consumption as possible for the march converters. Of the many converter types, the single-stage converter with a centrifugal turbine had proven to be the most suitable. It is simple in construction and, thanks to the high ring strength of its radial turbine, is very suitable for high speeds. It became the standard converter for Voith turbo transmissions.

At the beginning of the seventies, the development of the torque converter made it possible to achieve the required tractive force characteristics - up to the level of the starting tractive force - with a two-converter transmission instead of the previous three-converter transmission. Even today, the converter development is not complete, although it has reached a high level. Numerical flow simulations (Computational Fluid Dynamics - CFD) allow an insight into the entire flow field, even in areas of the rotating paddle wheels that are difficult to access for metrological reasons. The oil-filled flow space is modeled on the computer as a fine computational grid. The flow variables speed, pressure, etc. are then calculated for each grid node. In a subsequent analysis, the circulatory flow is made visible - for example by means of a three-dimensional streamline display. Mechanisms that reduce efficiency, such as eddies, flow separation on surfaces and incorrect flow to the blade rings, can thus be precisely localized. In addition to the visualization of these effects, it is also possible to account for the associated power losses.

This creates a connection between changes in the flow field and a change in the efficiency, from which possibilities for improvement can be derived. The calculated parameters agree very well with the measured values ​​over a wide operating range; deviations result from time-saving simplifications in the simulation. Optimizations of existing units as well as the development of new converter types can thus be carried out purely virtually on the computer. The prototype construction and the verification of the results in the experiment are at the end of the development process.

literature

  • Wolfgang Paetzold: Voith Turbo Gear 1930–1985, Volume 1 Locomotive Gear . Heidenheim, 2002.
  • Wolfgang Paetzold: Voith Turbo Gear 1930–1985, Volume 2 Railcar Gearbox , Heidenheim, 2004.
  • Voith Antriebstechnik, 100 years of the Föttinger principle . Springer-Verlag, ISBN 3-540-31154-8 , Berlin 2005.

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