For any transmission type the vehicle's responsiveness during large and/or fast engine speed shifts may appear reluctant or even counteractive. This is caused by unwanted inertial torques stemming from accelerating or decelerating the rotating elements within the engine and transmission. Reminiscent of comparable behaviour seen in aircraft jet-propulsion, this phenomenon is also referred to as 'jet-start'. To overcome this behaviour, a CVT powertrain is augmented with a powersplitting planetary gear stage and compact steel flywheel. The new transmission - coded Zero Inertia (ZI) powertrain - seamlessly combines two contradictive features: the driveability in terms of the pedal-to-wheel response is greatly improved and a large leap towards optimal fuel economy can be made. The latter is achieved by cruising the vehicle at extremely low engine speeds owing to the large ratio-coverage of the CVT. As for the driveability, the flywheel acts as a peak shaver. During engine speed shifts it delivers power at (semi-) pedal kick down (downshift) and absorbs kinetic energy of the engine sided powertrain elements at pedal back-out (upshift). In this paper, the behaviour of the ZI system is evaluated in 'tip-shift' mode. In that case the engine speed is linked to the wheel speed through 6 fixed CVT ratios. The engine speed can be altered by selecting different gears using a sequential gear selector stick. Even though this tip-shift mode for CVT equipped vehicles is not new, the appearance of the flywheel in the ZI powertrain will contribute to a different behaviour during gear shifts. These differences will be exemplified through simulation results obtained with three other transmission models viz. AST (Auto Shift Transmission), DCT (Double Clutch Transmission) and a basic CVT. In field experiments the tip-shift in a VW Bora test vehicle with ZI powertrain is compared with a commercially available Mini One with CVT. A test panel of 10 people drove the vehicles, executed predefined tasks and evaluated their findings. The results of these experiments are also reported in this paper.
Tip shift in the zero inertia powertrain
Kippschaltung bei der trägheitslosen Kraftübertragung
2002
15 Seiten, 8 Bilder, 8 Quellen
Conference paper
English
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