Abstract
KEYWORDS High-Speed-Gearing, NVH of Gears, Electrified Automotive Powertrain, Gear Design, Gear Vibration
ABSTRACT
Fully electrical driven vehicles have several advantages in comparison to concepts driven by combustion engines. Besides high power density, electrical drives feature a very low noise emission during operation. Nevertheless, new acoustic challenges come up for the design of transmissions to be integrated into the powertrain of fully electrically driven vehicles. The noise of a combustion engine, compared to low-noise electric drive, is unable to mask the gear noise, which shows an undesirable tonal character. In addition, the trend of electrified powertrains is towards higher input speeds, which increases the risk of resonance oscillations of the transmission gears. Gear design for electromechanical powertrains, therefore, has to focus on low excitation levels and operating strategies to reduce gear noise caused by resonance oscillations.
As part of the SPEED2E research project, which is sponsored by the Federal Ministry for Economic Affairs and Energy (BMWi) and supported by the Research Association for Power Transmission (FVA), a high-speed, electrically driven powertrain with input speeds of up to 30,000 rpm was developed. The prototype powertrain mounted on a test rig is designed to investigate the challenges for the transmission in terms of load-carrying capacity, efficiency and noise emission. Due to its highly functional layout with two subtransmissions, each driven by identical electric machines and connected to a common final drive, a flexible and comprehensive analysis of these challenges is possible. One subtransmission features two speeds so that three power paths can be used to transfer power to the driven axle. This layout enables the design of numerous possible operating strategies in terms of saving energy or reducing noise emission. Besides shifting without traction interruption, the power paths can be selectively loaded to increase the overall efficiency of the powertrain. Moreover, a specific loading and unloading of both sub-transmissions can be used to reduce or even avoid resonance oscillations during operation. In the context of this paper, a numerical-based operating strategy is presented, which reduces the dynamic gearing oscillations for all possible operating conditions of the powertrain to a minimum.