Bevel gears are widely used in various industrial applications, such as automotive, aerospace, and marine industries, due to their ability to transfer power between non-parallel shafts. The conventional manufacturing of bevel gears involves several time-consuming and costly processes, including gear blank preparation, gear cutting, and gear finishing. The increasing demands on gear components regarding increasing power density, reducing installation space, reducing weight, and increasing efficiency are also reflected in the design of gear components. The reduction of installation space and weight as well as the increase in power density often leads to an optimized wheel body design that interacts with the gearing in terms of load capacity and stiffness. This leads to an increase in the required geometric degrees of freedom (DOFs). Due to the resulting complex wheel body shapes and different production-related effects, production-related geometry adjustments may also be necessary. Tools for evaluating the gearing in combination with the wheel body shape and its influences nowadays form the basis for unlocking the holistic optimization potential of transmission components.
Standardized methods, like AGMA 2001-D04 or ISO 6336 for the calculation of the load carrying capacities of gears are intentionally conservative to ensure broad applicability in industrial practice. However, new applications and higher requirements often demand more detailed design calculations nowadays; for example: long operating lives in wind power gearboxes or fewer gear stages and higher speeds in e-mobility applications result in higher load cycles per tooth in a gearbox.
A calculation-based study of different variants with regard to contact ratio and tooth root geometry to compare the results from the 2019 version of ISO 6336 to the previous version, released in 2006.
Highly loaded gears are usually casehardened to fulfill the high demands on
the load-carrying capacity. Several factors, such as material, heat treatment, or macro and micro geometry, can influence the load-carrying capacity. Furthermore, the residual stress condition also significantly
influences load-carrying capacity. The residual stress state results from heat treatment and can be further modified by manufacturing processes post heat treatment, e.g. grinding or shot peening.
The objective of this work is to introduce a method for the calculation of the tooth root load carrying capacity for gears, under consideration of the influence of the defect size on the endurance fatigue strength of the tooth root. The theoretical basis of this method is presented in this paper as well as the validation in running tests of helical and beveloid gears with different material batches, regarding the size distribution of inclusions. The torque level for a 50 percent failure probability of the gears is evaluated on the test rig and then compared to the results of the simulation. The simulative method allows for a performance of the staircase method that is usually performed physically in the back-to-back tests for endurance strength, as the statistical influence of the material properties is considered in the calculation model. The comparison between simulation and tests shows a high level of accordance.
Reduced component weight and ever-increasing power density require a gear design on the border area of material capacity. In order to exploit the potential offered by modern construction materials, calculation methods for component strength must rely on a deeper understanding of fracture and material mechanics in contrast to empirical-analytical approaches.
The common calculation methods according to DIN 3990 and
ISO 6336 are based on a comparison of occurring stress and
allowable stress. The influence of gear size on the load-carrying
capacity is considered with the size factors YX (tooth root bending)
and ZX (pitting), but there are further influences, which
should be considered.
In the following, major influences of gear size on the load factors
as well as on the permissible tooth root bending and contact
stress will be discussed.
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