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advanced simulation technologies TRANSMISSION SIMULATION FOR POWERTRAIN OPTIMIZATION The demand to reduce CO2 emissions and consumption by optimizing the overall system, the more widespread use of different types of transmissions and the trend towards electrification are making it increasingly necessary to perform a detailed analysis of the transmission in the design phase – in addition to the basic dimensioning that takes place in the concept phase. F O C U S 2 1 > Transmission acoustics – the effect of rattle and whine on airborne noise. SIMULATION REQUIREMENTS Current internal combustion engine developments, aiming at achieving reduced consumption and lower CO2 emissions, also have an effect on the transmission. Approaches like downsizing and down-speeding while enhancing the performance are leading to higher excitations and rotational speed irregularities, which, in part, are transferred to the transmission – with the potential of affecting transmission acoustics adversely. It is therefore essential to be able to calculate and optimize the interaction of the subsystem – the transmission in combination with the internal combustion engine and the rest of the powertrain. Apart from the structural dynamics, attention must also be paid to friction, including hydrodynamic resistances. COMBINED MBD/CFD WORKFLOW For this engineering task, AVL has added further models for transmission and powertrain components to its structure dynamics software AVL EXCITE™. These include clutch, dual-mass flywheel and torque converter. A variety of modeling depths are available for the gears including a three-dimensional contact model for cylindrical gears, which takes into account the involute toothing with profile modifications and gear meshing errors. The application scope for transmissions – as a subsystem, coupled with the internal combustion engine or the entire powertrain – comprises the investigation of dynamic behavior under stationary and nonstationary operating conditions, the detailed determination of all mechanical losses, component durability and transmission acoustics. An efficient sound radiation calculation supports the assessment of specific acoustic phenomena, such as transmission whine and rattle, based on airborne noise results. The workflow is complemented by the CFD software AVL FIRE™ for calculating hydrodynamic losses caused by rotating components splashing in oil and by oil mist. Combined with the mechanical losses from the AVL EXCITE™ calculation, this allows to assess the efficiency of different design variants, and serves as an input for further fuel consumption and vehicle thermal management calculations. Based on the CFD simulation results, the hydrodynamic-related drag torque is determined additionally – an essential influencing parameter on gear rattle that is used as a boundary condition in the simulations with AVL EXCITE™. In this combination, AVL’s simulation solution provides all the tools to find the optimal configuration in terms of efficiency, weight and acoustics within the design phase.  <


Focus_2016_02_E
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