Turbo transmissions are hydrodynamic, multi-stage drive assemblies designed for rail vehicles using internal combustion engines.
Since then, improvements to turbo-transmissions have paralleled similar advances in diesel motors and today this combination plays a leading role worldwide, second only to the use of electrical drives.
This is where turbo-transmissions differ from similar hydro-static transmissions, which operate using low flow rates, and high pressure according to the displacement principle.
Turbo transmissions are hydrodynamic, multi-stage drive assemblies whose performance is based on the Föttinger principle of fluid dynamics.
Torque converters, fluid couplings and optional hydrodynamic retarders are the key components in these assemblies, which are ideally suited for powered rail vehicles.
Together, all these engineering improvements had a common goal: to continually increase the transmission's performance rating without compromising its installation complexity or proven reliability.
In 1969, the smaller T 211 turbo-transmission was developed as an alternative to hydro-mechanical bus transmissions, being designed for diesel railcars in the low power range of 200 to 300 hp (149 to 224 kW).
As a result, the T 211 r had reserve power, which was reflected by its reinforced mechanical components (gears, bearings and shafts) as well as the transmission controls.
When viewed from the outside this T 211 r transmission differed from its predecessor, the T 211 re.3 with 320 kW (429 hp), only slightly through the addition of a built-in electronic control unit and an enlarged air filter.
To shorten the transmission's overall length, a twin shaft construction was used over the high gears, which was similar to the design used in reversing units.
The T 212 bre had the same hydrodynamic circuit dimensions as the T 211 r, but it had the further advantage of greater coupling efficiency for trains operating at only 50% of their maximum speed.
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.
Modern computational fluid dynamics (CFD) can now provide engineers with detailed information on the flow-patterns inside a rotating turbine wheel.
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.