Optimum dog-leg angle for mass and bearing force optimization of multistage gear reduction

This paper describes a method to minimize bearing forces as well as bearing and housing mass for a multistage gear reduction. This is done by finding the optimum dog-leg angles for the stages while leaving other aspects of the design unaltered. The optimization is demonstrated first for spur gears, and then for helical gears typically used in electric vehicles. A numerical example shows how bearing forces and mass of bearings and housing are reduced considerably by choosing the optimum dog-leg angle.

Duncan Dowson: Pioneer of elastohydrodynamic lubrication of gears

The paper briefly reviews Duncan Dowson's ground-breaking contribution to the theory of elastohydrodynamic lubrication in relation to the understanding of lubrication of gear tooth contacts. His early work with Higginson on numerical modelling of elastohydrodynamic lubrication finally explained how gears can operate successfully, and avoid wear, due to the generation of a stiff, protective oil film. The resulting minimum film thickness equation stands as a reliable reference formula for calculations in gear design standards. The paper includes examples of how elastohydrodynamic lubrication theory has been developed by the present authors and their co-workers, and applied to aid the design of engineering components such as worm gears, thrust rims and profile-modified helical gears. Also included is its extension to include the important effects of surface roughness at the asperity level (micro-elastohydrodynamic lubrication) and its relevance to the current, troublesome problem of micropitting.

Effect of Transformation Plasticity on Gear Distortion and Residual Stresses in Carburizing Quenching Simulation

This paper addresses the effect of gear steel on distortion and residual stresses due to phase transformation in carburizing and quenching. In particular, the martensitic and bainitic phase transformation expansion and transformation plasticity properties of two automotive gearbox steels (20CrMnTiH and 20MnCr5) and their physical parameters are measured by experiments of transformation plasticity properties. Numerical simulations of the actual carburizing and quenching process of the gearbox spline helical gears were carried out in combination with the thermal and mechanical properties with temperature variations calculated by the material design software JMAT-Pro. In particular, the phase transformation properties of the two materials and their influence on the distortion and residual stresses after carburizing and quenching were verified by experiments of transformation plasticity and numerical simulations. A reliable basis is provided for predicting the distortion mechanism of gear steels in carburizing and quenching.

Tooth surface modification of double-helical gears for compensation of shaft deflections

Based on gear meshing theory, the tooth surface equation with tooth profile modification parameters is deduced, the tooth surfaces of unmodified and modified gears are constructed, the three-dimensional model of unmodified and modified double helical gear-shaft-bearing system is established and then the three-dimensional contact finite element model of double helical gear-shaft-bearing system is established and the load-bearing contact analysis of the tooth surface is carried out. The actual contact state of the tooth surfaces of double helical gears under different shaft stiffness and power transmission paths is investigated, and the influence of tooth modification parameters on the load distribution of the tooth surfaces of double helical gear pairs is studied. The results show that the tooth surface bearing the contact of the herringbone gear system has the phenomenon of partial load due to the supporting deformation, and the unmodified herringbone gear has obvious contact stress concentration. However, the phenomenon of partial load and stress concentration can be effectively improved by gear tooth modification.

Low excitation spur gears with variable tip diameter

One important source of noise in drive trains are transmissions. In numerous applications, it is necessary to use helical instead of spur gear stages due to increased noise requirements. Besides a superior excitation behaviour, helical gears also show additional disadvantageous effects (e.g. axial forces and tilting moments), which have to be taken into account in the design process. Thus, a low noise spur gear stage could simplify design and meet the requirements of modern mechanical drive trains. The authors explore the possibility of combining the low noise properties of helical gears with the advantageous mechanical properties of spur gears by using spur gears with variable tip diameter along the tooth width. This allows the adjustment of the total length of active lines of action at the beginning and end of contact and acts as a mesh stiffness modification. For this reason, several spur gear designs are experimentally investigated and compared with regard to their excitation behaviour. The experiments are performed on a back-to-back test rig and include quasi-static transmission error measurements under load as well as dynamic torsional vibration measurements. The results show a significant improvement of the excitation behaviour for spur gears with variable tip diameter.