The acoustic behavior of technical products—referred to as Noise, Vibration, and Harshness (NVH)—forms an important criterion in customers’ purchasing decisions, e.g. in the automotive sector. Thus, optimizing the NVH behavior is essential during product development. NVH is influenced by dynamic excitations and the transfer of sound from the location of excitation to a receiver such as the driver. As the electrification of the mobility sector increases, gear mesh excitations contribute significantly to the noise of a vehicle, which was previously dominated by the combustion engine. The time-varying stiffness of the gear mesh is the main excitation in drivetrains and therefore needs to be optimized during product development. Elastic multi-body simulation (eMBS) has become an established method for modeling NVH characteristics of drivetrains. In order to evaluate the effect of gear mesh designs on a drivetrain’s excitations and therefore its NVH behavior, the time-varying stiffness of the gear mesh has to be incorporated into eMBS models. Today, this is either done by applying quasi-static transmission errors onto a model in frequency domain thereby neglecting the influence of the system’s oscillations back on the gear mesh excitations, e.g. by axial misalignment of the meshing shafts. Alternatively, analytical stiffness calculations are included in eMBS models in time-domain. However, these approaches are not yet validated. Also, incorporating the interaction between a flexible gear wheel and the gear mesh stiffness is paramount for NVH models of gears. Within previous works, a method for incorporating externally calculated gear mesh stiffnesses into eMBS has been proposed to overcome these challenges. The goal of this paper is to compare, validate and enhance the existing eMBS modeling methods of gear mesh stiffnesses with respect to their ability to model the dynamic behavior of gear boxes, defined by natural frequencies and critical operating points. A two-step approach consisting of quasi-static and dynamic validations is conducted. An improvement in accuracy between simulation and measurement of 10 dB is achieved compared to analytical eMBS methods.

One challenge in the design of automotive gearboxes is the combination of high power density, high efficiency and low noise emission. With the electrification of the powertrain, the requirements in terms of noise emission and efficiency increase additionally. Stepped planetary gear stages are a potential topology to solve the current challenges in gearbox technology. Current research shows the pronounced misalignment behavior of planetary gear stages, especially with manufacturing or assembly deviations. However, the effects of dynamic misalignment behavior on tooth contacts in stepped planetary gear stages have not been adequately investigated. This paper presents a test rig that allows the investigation of the excitation and displacement behavior of stepped planetary gear stages taking into account adjustable axis misalignments. The axis misalignment of the stepped planetary shafts is introduced with eccentric bushings in this test rig concept. To evaluate the excitation and displacement behavior the transmission error and the displacements of different components can be measured. The test rig is modeled in the dynamic multibody simulation. The tooth contact is modeled using the force module GearForce6D. The axis misalignment is varied in the simulation model and the influence on the excitation and displacement behavior is evaluated. The simulation results show that planet pin position errors have the highest influence on the sun trajectory and the load sharing. The misalignments occurring in the tooth contacts due to inclination and skew of the stepped planetary shaft lead to higher tooth flank pressures and an increase in the total transmission error.

Planetary gears are widely used in large transmission applications, such as wind turbines, hydropower plants and industry, due to power density, high gear ratio and efficiency advantages. The advancement of predictive maintenance and gear system design processes is essential to enhance the ratio between durability and used material of gearbox components. Preventing possible downtime due to unforeseen failures in between maintenance intervals also increases resource efficiency. In this paper, a quasi-static FE-based method is presented that calculates the running behavior of planetary gear stages considering time variant and time invariant axis misalignments, tooth flank deviations as well as the influence of coupled meshing areas. A contact algorithm is presented, taking into account load dependent deviations of an adjustable sun gear onto the contact behavior, which is widely used to compensate load-sharing issues. The model can consider these deviations and their influence on the contact behavior hence their characteristic frequency order spectrum. In the future, vibration signatures taking into account manufacturing as well as load dependent deviations can be created to help identifying misalignments in transmission error data. The method can then be used for end of line tests as well as the evaluation of the rest of useful life based on local pressure distributions and tooth root stresses.

In many applications of cylindrical gearboxes, the reduction of noise from the gear mesh is an important criterion. In addition to electrified vehicle drives, gear excitations also play an important role in stationary applications such as wind turbines. When designing gearboxes, elastic surrounding structures or material combinations are increasingly being used in order to reduce mass and manufacturing costs. This has a decisive effect on the misalignment behavior of the cylindrical gears and the need for micro geometric corrections. At the same time, it must be taken into account that deviations can occur during the production of the micro geometries, which must be tolerated and have different effects on the NVH behavior. The aim is to develop a method for the design of profile corrections for elastic environmental conditions and materials. It takes into account that the nominal design is subject to different manufacturing deviations, which have to be tolerated. This is done by means of a tolerance design mechanism that determines the best compromise between tolerance definition and manufacturing costs depending on assumptions for the relationship between manufacturing accuracy and resulting costs. In the first step of the nominal design, the load-dependent misalignments are determined by FE-simulation. This is followed by an optimization of the micro geometric gear profile using a penetration calculation in order to optimize the excitations and improve the NVH behavior. An AI-supported substitute model of the excitation behavior of the entire gearbox is then determined. This is used to determine a suitable compromise between tolerance requirements and expected production costs using a metaheuristic optimization process. This is demonstrated using a cylindrical gearbox for electric cars. The calculation method presented enables the design of profile modifications and production tolerances using modern tools and shows further potential for noise reduction.

This report presents a new method for calculating and designing grinding worm geometries for continuous generating grinding in order to realize targeted micro geometry scattering on gear flanks. The method uses the idea to transfer the ideal micro geometry onto the worm topography utilizing a reversed rolling calculation. First, the reversed calculation of the grinding worm flanks is carried out by gradually breaking down a specified gear geometry with varying micro geometries into individual profile cross-sections. Afterwards, these profile cross-sections are transformed into a grinding worm geometry whose starts can manufacture different modifications. The grinding worm topography is calculated using an exemplary application in which targeted micro geometry scattering on a cylindrical gear is reverse generated onto the generating profile and then onto the grinding worm body. The example serves to verify the method. The calculated grinding worm geometry is used for forward generation of the flank geometries and kinematic differences between the nominal and actual geometry of the gear flanks are shown as a comparison. A key advantage of this new approach is the avoidance of periodically repeating ripples on the tooth flanks, which occurred when using previous approaches to manufacture targeted micro geometry scattering in the generating grinding process due to differently dressed grinding worm starts. The new approach uses a dressing gear for shaping the grinding worm geometry. It achieves an improved NVH behavior of the gear pair concerning the tonality through varying flank modifications by utilizing the topographically shaped grinding worm starts. This was verified as part of a quasi-static tooth contact analysis in which the derived grinding worms were used to generate replica of dressing gears and investigate the acoustic excitation behavior. The simulation results show significantly reduced levels of the transmission error in the gear mesh orders and at the same time lowered tonal noise components, which indicates a subjectively more favorable noise behavior.

Dynamic multi-body simulation models of the entire system are particularly important for the development and analysis of gearboxes. With the help of these models, the operational behavior of the gearbox can be examined in detail, without having to produce a prototype. This makes it possible to investigate the influence of various factors, such as misalignments, deformations of components or the usage of different structural components, on the operational behavior of the gearbox. The modelling of the gear mesh is particularly relevant in order to be able to model the behavior of the gearbox realistically. If the gear mesh should be calculated with an enhanced level of detail, numerical FE-based tooth contact analyses are used for each integration step of the dynamic model. These calculate the forces and torques in all spatial directions on the gears based on translational and rotational positions of the gears in contact. However, the disadvantage of this highly precise method is the longer calculation time that results from solving the FE-based tooth contact for each calculation step and prevents efficient use in product development. To improve the calculation time of the model, an AI model, e.g. a neural network, will be used instead of the time-consuming FE-based tooth contact calculation. The neural network reduces the calculation time of the dynamic multi-body model from several hours to just a few minutes. This enables the efficient use of highly accurate gear modelling in dynamic multi-body simulation. The development is carried out as User Force in the simulation software Simpack.