Advanced Development of Torque-Converters
In turbo-transmissions, the torque-converter is clearly the centerpiece of the entire construction and over the past decades its continuous improvements have been primarily responsible for satisfying the steadily increasing demands of diesel powered vehicles. Here, the goal of each improvement has been greater efficiency and better start-up performance, without compromising the start-up converter's dimensions as well as consistent loading of the travel-phase converter when in transit. Of the many different torque-converter designs, the single-stage converter using a centrifugal-flow turbine has proven to be the best. It has a relatively simple construction and due to the radial stability of its turbine the converter is well suited for high rpm operations.
In the 1970s, thanks to new torque-converter developments with improved traction characteristics, (approaching the start-up traction) a two-converter transmission was designed to replace the previously used three-converter transmission. And even today, torque-converters are still being improved, although they have reached an advanced stage. Modern computational fluid dynamics (CFD) can now provide engineers with detailed information on the flow-patterns inside a rotating turbine wheel. Here, the oil-filled circuit in which the turbine turns is portrayed as computerized grid showing the flow characteristics at each grid intersection. For each of these points, the flow volume, speed, and pressure can be calculated. Later during the analysis phase, a three dimensional model of the circuit's flow pattern can be viewed and flow disruptions which reduce the converter's efficiency can be identified, such as: eddies, surface turbulence and mis-directed fluid-flows along the turbine wheel. In addition, aside from visualizing these flow disruptions engineers can also use CFD to calculate the resultant loss in converter efficiency.
In the end, the relationship between changes in a converter circuit's flow-patterns and the efficiency of a torque-converter can then be used to identify potential improvement areas. To a large extent, the predicted values match well with the actual operational measurements, although some differences do occur due to the use of time-saving simplified simulations. Still, CFD allows the optimization of existing converters as well as the development of new virtual-converter types via computer. Afterwards the building of a prototype and the verification of the actual performance results concludes the development phase.
Read more about this topic: Voith Turbo-Transmissions
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