Voith Turbo introduced a new hydrodynamic interface between engine and transmission for heavy trucks at the IAA Commercial Vehicles show in Hannover, Germany. The company produces hydrodynamic retarders for trucks and buses, designed to apply secondary braking through the driveline to reduce wear and potential brake fade during long descents. Normally, the retarder is fitted to the output side of the gearbox between the transmission and propshaft. For the retarder, the normal drive sequence is reversed, with the hydrodynamic circuit triggered by torque from the drive wheels through the propshaft.
With the Voith VIAB, the system is fitted between the engine and transmission, potentially integrating the functions of the retarder and torque converter or clutch. The VIAB consists of a hydrodynamic circuit with impeller and turbine wheel—the expected components of a retarder. Additionally, the VIAB includes a turbine brake and a lock-up clutch.
According to Voith, the VIAB can handle torque greater than 3000 N·m (2210 lb·ft). Functioning as a torque converter, the system can be used with engines producing power outputs between 400 hp (298 kW) and over 600 hp (448 kW). In this way, the VIAB can transmit engine torque from low engine speeds to start the vehicle moving, without the wear associated with a friction clutch. Like modern torque converter systems, the lock-up clutch is engaged at higher vehicle speeds to overcome the inefficiencies of a fluid transmission.
The flexibility of the VIAB is achieved through a variable-speed hydrodynamic coupling. The volume of oil in the system between impeller and turbine wheel is changed by filling and draining. This means that the torque-handling characteristics of the system can be dynamically adapted to suit the output of the engine as well as the needs of the driver or driving situation. Hence, the same system can be applied to a wide range of engine outputs.
The hydrodynamic elements of the system, therefore, provide torque transfer from engine to transmission or the retarding function, as required. According to Voith, the VIAB can reduce fuel consumption because there is no oil pump, as would traditionally be used with a retarder. In addition, the hydrodynamic coupling is drained with the gears engaged, while the vehicle is at rest. This reduces load on the engine, helping to reduce fuel consumption further.
The VIAB also can offer a weight reduction because there is no need for a separate clutch or torque converter and retarder.
The first installation of a VIAB has been to a Mercedes-Benz Actros heavy haulage tractor. Voith expects to see other applications in vehicles used in construction, refuse collection, and distribution vehicles.