Torque converter (hydrodynamic)

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ZF torque converter at BAUMA 2007
Torque converter (cutaway model) Porsche Museum Stuttgart

A hydrodynamic torque converter or Föttinger converter is a hydrodynamic transmission . It was originally developed by Hermann Föttinger for ship propulsion and was later used in motor vehicles and locomotives (see also Föttinger principle ).

The special Trilok converter has been used as a starting element in motor vehicles with automatic transmissions for a long time . The specialty of the Trilok converter is that when starting with a low torque at the drive, a high torque is generated at the output that is stationary or rotating at low speed. The converter changes continuously and automatically from a low drive torque at a high drive speed to a high output torque at a low speed or at a standstill with constant engine power. The conversion range is up to 1: 3 (the output torque is three times the input torque).

In general, each gear train can be both a speed converter and a torque converter.

history

Wandler and Trilok have been known since the beginning of the 20th century. Hermann Föttinger provided a first description of such a transmission in 1905 in his patent application for a “ fluid transmission with one or more driving and one or more driven turbine wheels for transferring work between adjacent shafts ”. In a later patent in 1915, Föttinger presented a much more compact solution as a “ fluid transmission for transferring work between adjacent shafts by means of driving and driven turbine wheels ”, which is very similar to the later series converters. In 1925, the Föttinger coupling was tested in prototypes. The Trilok converter was developed in 1928. In 1948 General Motors built a Föttinger clutch into a motor vehicle as standard for the first time ( Buick Dynaflow ). A transmission with a Trilok converter appeared at Borgward in 1955. In the period that followed, numerous refinements were brought onto the market, for example converter lock-up clutches, simplified production through sheet metal forming, integration of torsion dampers and dual mass flywheels.

technology

Demarcation

The Föttinger coupling only has a pump and turbine wheel, so that there is a speed difference between input and output, but the input and output torque remain the same, i.e. they do not convert any torque. The torque converter builds on it, but has one or two stationary idlers that divert the flow of oil.

functionality

A torque converter is made in the simplest case from the components pump impeller , turbine runner and stator , which are installed in a common oil-tight housing. The principle of hydrodynamic power transmission is that a liquid (oil, water or similar) is captured and accelerated by the blades of the pump wheel. The pump wheel, which is driven directly by the motor, converts the mechanical energy into flow energy, it forms the so-called primary side. The turbine wheel, which is directly connected to the transmission output shaft (secondary side) in pure hydrodynamic transmissions , absorbs this flow energy again and provides mechanical energy to the output of the converter. The stator is firmly connected to the housing and therefore cannot turn. The vanes of the stator, which are curved by around 90 degrees, deflect the oil and thereby cause a greater torque on the vanes of the turbine wheel. At the same time, the reaction element (stator) also experiences a corresponding torque that must be supported. The stator is necessary as a torque support , since otherwise the torque cannot be increased and only the function of a pure clutch would be achieved. Furthermore, the stator directs the oil flow back to the blades of the pump wheel at a favorable angle, so that the oil circuit is self-contained. The power that can be transmitted also depends on the speed and increases with it.

The torque conversion depends on the speed difference between the pump and turbine wheel. The greater the difference, the greater the torque increase can also be. If the two speeds equalize, the efficiency and the torque increase of the converter decrease. There are several possible solutions to achieve a consistently high level of efficiency : In large gearboxes, several hydraulic circuits are usually used for different speed ranges, which are automatically filled or emptied accordingly.

Trilok converter

In the so-called Trilok converter , the stator wheel is mounted on a freewheel so that the converter automatically switches to a pure hydrodynamic clutch ( clutch area , i.e. clutch without changing the torque); the stator rotates freely after switching over, so that no more torque can be supported and the input and output torques are the same.

In contrast to simple hydrodynamic clutches, which were previously used in automatic transmissions under the name "Föttinger clutch", a torque converter and a Trilok converter can be recognized by the fact that, in addition to the input and output, a torque support, for example as a fastening to the Housing, is required.

A lock-up clutch (converter lock-up clutch, short: WÜK) is used in newer automatic transmissions. This connects the input shaft directly to the output shaft. The efficiency increases to almost 100%. However, the torque and speed on the input and output shaft are the same.

The converter also dampens torsional vibrations in the drive train so that excitations from the engine are not transmitted to the body via the cardan and drive shafts .

Installation in vehicles

Torque converter (top right) in a construction machine transmission

The torque converter is typically used in automatic transmissions in motor vehicle and construction machinery construction and connects the crankshaft with the other parts of the automatic transmission . In locomotives and shipbuilding, pure hydrodynamic transmissions are often used that contain multiple torque converters or hydraulic clutches.

Since the efficiency of a torque converter rarely exceeds 85% and is around 95% in the clutch range of a Trilok converter, a noticeable part of the transmission input power is converted into heat that has to be dissipated. This is why part of the working fluid is kept in constant circulation and cooled. The use of a converter lock-up clutch significantly reduces the power loss. The clutch is often used in low gears and the torque converter is largely limited to its function as a starting element. When starting off, a Trilok converter offers greater efficiency than a conventional slipping clutch thanks to the increased torque.

By bridging the torque converter, the efficiency improves, but the vibration-damping effect is also eliminated, since the power transmission takes place via the mechanical frictional connection and no longer via the hydraulic fluid. In order to meet the comfort requirements here, so-called turbine torsion dampers (TTD) can be used. Another way of minimizing this disadvantage is not to close the converter lock-up clutch completely, but rather to operate it with a load and speed-dependent slip speed . The heat generated in the friction elements of the lock-up clutch must, however, also be dissipated via a sufficiently dimensioned, continuous exchange of the fluid in the converter.

See also

literature

  • Hans Joachim Förster: Infinitely variable vehicle transmissions in mechanical, hydrostatic, hydrodynamic, electrical design and in power distribution: Basics, designs, interaction , ISBN 3-8249-0268-0 , Verlag TÜV Rheinland
  • Johannes Feihl: The diesel locomotive. Transpress, Stuttgart 2009, ISBN 978-3-613-71370-3 .
  • Harald Naunheimer, Bernd Bertsche, Gisbert Lechner. Vehicle transmission. 2nd edition, Springer, Berlin / Heidelberg / New York 2007, ISBN 978-3-540-30625-2 .

Animations

Web links

Commons : Torque Converter  - Collection of Images, Videos and Audio Files

Individual evidence

  1. Naunheimer et al., " Vehicle transmission" (see list of literature), Section 1.2.5 from page 23
  2. dpma.de - German Reich Patent of 1905; Patent: DE221422; Pages: 9 (last accessed July 18, 2017)
  3. dpma.de - German Reich Patent of 1905; Patent: DE238804; Pages: 4 (last accessed on July 18, 2017)
  4. ^ 1948, Buick Takes the Transmission a Step Further , gmheritagecenter.com