The fuel economy of a vehicle equipped with an internal combustion engine can be improved by operating the engine at low rotational speeds where its optimum efficiency is found, also known as E-line tracking. However, if the engine is not oversized, this will significantly reduce the acceleration potential. An assist is then needed to guarantee an immediate response. This paper presents an alternative drivetrain concept in which the SA is connected to the primary and secondary side of a continuously variable transmission (CVT) through a planetary gear set. In this so-called Zero Inertia configuration (ZI), the inertia of the SA (Starter Alternator) will act as a mechanical torque-assist by accelerating in the opposite direction of the engine during a fast downshift. Compared to the crankshaft mounted SA, this alternative drivetrain will greatly improve the acceleration response without compromising the fuel economy of a CVT in eco-mode. The addition of an SA to a drivetrain can significantly reduce the fuel consumption of a vehicle through regenerative braking (5 %) and a stop-go strategy (4 %). Lowering the engine speed or E-line tracking can further decrease fuel consumption by 8 %. This strategy will only be accepted by the driver if the driveability is not compromised. The SA-CVT configuration can not meet this requirement because the SA does not have enough power to enable an immediate response at higher vehicle speeds. The functionality of the SA is greatly improved by mounting the SA in a Zero Inertia configuration. The inertia of the SA will act not only as an electric torque -assist but also as a mechanical power-assist by accelerating in the opposite direction of the engine during a fast downshift of the transmission. This configuration is therefore able to maintain a low engine speed and still have an immediate acceleration response available at high vehicle speeds. Compared to the standard CVT in sport-mode, an improvement in fuel economy of up to 15 % is possible. Currently under investigation for further enhancement of the SA-ZI transmission are: -Reducing the torque transmitted through the CVT bell during launching and acceleration by applying an electric torque of the SA. This increases the torque capacity of the CVT. Optimising the ratios of the planetary gear set to increase the effectiveness of the power-assist and fuel economy; -Replacing the CVT with an Automated Manual Transmission (AMT), while eliminating the torque interruption using the inertia, i.e. applying the energy stored in the rotating inertia of the SA. This will enable a significant cast and weight reduction with respect to a standard AT or CVT; -Downsizing of the engine to further reduce fuel consumption, weight and packaging space.
Starter alternator in zero inertia configuration: expanding the functionality of the zero inertia drivetrain
'Starter Alternator'-Aggregate in trägheitslosen Konfigurationen
2002
17 Seiten, 9 Bilder, 5 Tabellen, 5 Quellen
Conference paper
English
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