Abstract
Modern vehicle transmissions are compact multi-stage multi-speed gearbox designs that meet the goals of low weight, high power and fulfill package restrictions. The shaft layout, gear locations and mesh ratios are designed by mathematical methods implemented in special software. These parameters are fixed before the actual gear and flank design takes place. The surrounding construction leaves little room for constructive improvements and may not be capable to support the gears optimally. The demand for a robust and very low noise design leads to increasingly major challenges for the gear engineer. More detailed and thorough simulation methods are required to reach the goal of silent gears.
The Gear Research Center located at Technische Universität München has been developing methods to determine gear mesh properties and design optimal gear macro- and micro geometry for the transmission industry for many years. Special emphasis is set on the behavior of the shaft and bearing system and its effect on meshing conditions. The above mentioned design restrictions are met by detailed analysis of main gear geometry and flank modifications. Concerning load carrying capacity and especially noise excitation, adequate flank modifications are to be designed. Common evaluations of the design parameters lead to the distribution of Hertzian contact pressure on the tooth flanks, tooth root stress in the fillet and the transmission error (TE) for a range of loads. Since the flank modifications affect every goal individually, a trade-off is required and an optimum has to be found. Increasing profile ratio under high load as well as partial contact patterns under low loads have to be considered. Reaching optimal design is dependent on being able to account for all relevant effects in simulation.
A methodology is described using software developed at FZG to handle the conflict. The phenomena that are covered by the method are described in detail. The paper shows that optimal flank modifications for low loads lead to mesh interference at higher loads. Focusing only on TE without regard for the load distribution may not lead to reliable results. Optimal flank modifications are always a compromise which has to be carefully balanced.
KEYWORDS – gear design, flank modifications, transmission error, dynamic tooth force, mesh interference