Whereas the existing Series III IVT is primarily used for development purposes, the optimised Series III IVT has been designed with productionisation in mind. The Series III prototype, installed in an SUV, proved the potential of this technology in terms of fuel economy and driveability. However, inevitable compromises at the development stage had to be made which affect the performance and the efficiency of the system and in order to improve these, rigorous optimisation work has been carried out in key areas such as the variator, the hydraulic control system and the shunt layout. For IVT systems it is imperative to examine not only the efficiency at component and sub-system level, but also the efficiency of the complete powertrain, which can best be measured in terms of specific fuel consumption and fuel economy. In other words, replacing conventional automatic transmissions with an IVT, results in an efficiency improvement of the overall system. This is possible, because the IVT allows the internal combustion engine to be operated in the most beneficial regions of the sfc map and also eliminates the need for an inefficient starting device in the form of a torque converter or friction clutch. The OEMs, legislators and most importantly the end-customers, are very interested in good fuel economy and the corresponding reduction of CO2 emissions (e.g. CAFE, ACEA). When compared to the series production 4 speed automatic transmission, the Series III IVT achieved fuel economy improvements of approximately 20 % on the US combined Metro-Highway drive cycle. Simulation studies have shown that this figure can be increased to 24 % by improving the system efficiency of the IVT. Further simulation work indicates thaI efficiency improvements become more important when comparisons with 5 and 6 speed automatic transmissions are made and importantly significant fuel economy benefits are achievable by using IVT technology. It was also shown that through optimisation of the IVT shunt layout it is possible to match or even exceed the performance of the standard automatic transmission, without sacrificing significant fuel economy benefits. Moreover IVT equipped powertrains offer higher comfort standards to the vehicle occupants because their of improved driveability (e.g. no gear change shift shocks, low rpm cruising) and useful features like hill hold and controlled hill descent, which are straightforward to implement with an IVT.
System efficiency optimisation of the torotrak Infinitely Variable Transmission (IVT)
Optimierung des Systemwirkungsgrades der Torotrak-IVT-Kraftübertragung
2002
14 Seiten, 19 Bilder, 2 Tabellen, 13 Quellen
Aufsatz (Konferenz)
Englisch
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