Effect of teeth micro-geometrical form modification on contact kinematics and efficiency of high performance transmissions

Light weight, compactness and efficiency are key objectives in high performance vehicular transmission systems, which are subject to large variations in torque and power. Pitch line velocities of up to 52 m/s and teeth pair contact pressures of up to 3 GPa are routinely encountered under race conditions. Contact patch asymmetry due to angular misalignments between input and output shafts leads to the generation of high edge stress discontinuities on gear flanks, inducing fatigue spalling which affects system durability. Crowning is widely used as a palliative measure to mitigate these undesired effects. These problems can be further exacerbated by contact footprint truncation. The paper presents a new approach to modelling the kinematics and contact micro-geometry of meshing conjunctions of involute spur gears with profile and lead modifications. A time-efficient analytical method is presented to accurately determine the contact footprint and kinematics, leading to the solution of highly loaded non-Newtonian mixed thermo-elastohydrodynamic contact under the extreme prevalent conditions of high performance vehicular transmissions. The effect of tooth form modification on contact footprint truncation, contact kinematics and generated frictional power loss is investigated. This approach has not hitherto been reported in literature

Boundary Conditions for Elastohydrodynamics of Circular Point Contacts

The paper presents the solution of an elastohydrodynamic point contact condition using inlet and outlet lubricant entrainment with partial counter-flow. The inlet and outlet boundaries are determined using potential flow analysis for the pure rolling of contiguous surfaces. This shows that Swift–Stieber boundary conditions best conform to the observed partial counter-flow at the inlet conjunction, satisfying the compatibility condition. For the outlet region, the same is true when Prandtl–Hopkins boundary conditions are employed. Using these boundary conditions, the predictions conform closely to the measured pressure distribution using a deposited pressure-sensitive micro-transducer in a ball-to-flat race contact. Furthermore, the predicted conjunctional shape closely conforms to the often observed characteristic keyhole conjunction through optical interferometry. The combined numerical–experimental analysis with realistic boundary conditions described here has not hitherto been reported in the literature

Roller bearing dynamics under transient thermal-mixed non-Newtonian elastohydrodynamic regime of lubrication

The paper describes a combined tribodynamics analysis (dynamics and contact tribology) of cylindrical roller bearings of a heavy duty truck transmission under high applied loads. The dynamic analysis provides the transient variations in contact load. It also determines the vibration spectrum of the bearing as well as that of contact dynamics. It is shown that with sufficient preloading and/or interference fitting a widely spread loaded region results, which reduces bearing-induced vibration. The transient tribological analysis, including thermal analysis with a novel and realistic lubricant inlet boundary condition demonstrates that non-Newtonian mixed elastohydrodynamic regime of lubrication is prevalent, but with reduced friction compared with unrealistic dry Coulombic friction, which is often assumed in literatur

Tribology of power train systems

The 2017 edition of Volume 18 builds on articles devoted to specific friction- or wear-critical components supported by coverage on the fundamental physical principles of friction, lubrication, and wear. In addition to basic concepts, methods of lab testing and analysis, materials selection, and field diagnosis and monitoring of friction and wear are also covered. The 2017 edition of this volume has undergone a significant expansion and revision of coverage by a new group of global experts. It has been updated with numerous material and technology developments on coatings, lubrication, tool and die wear, and a number of typical tribological components or classes of components. While it is impossible to include all the types of moving mechanical assemblies that pose tribological challenges, Volume 18 emphasizes a structured approach in analyzing complex tribosystems involving thermal, mechanical, materials, and chemical influences. The new Volume 18 provides an essential resource for a broad audience including researchers, engineers, technicians, students, and quality control personnel. The sections on solid friction, lubricants and lubrication, and wear and surface damage contain basic physical principles that help to introduce the materials-oriented professional to established concepts in tribology. The Handbook is also intended for use by individuals with a background in mechanics or lubricant chemistry seeking information on trends and developments on materials and coatings