International Journal of Powertrains (5 papers in press)
Special Issue on: ICAVP2017 Vehicle Transmissions
Vibration response from the planetary gear with flexible ring gear
by Song Xue, Ian Howard
Abstract: This paper aims to investigate the vibration response from the planetary gearbox with a flexible ring gear, which can be supported by various constraints and consequently result in quite different vibration spectra. The ring gear with its supports was modelled as a moving load problem on the finite element beam to formulate the vibration response in this research. The number of the beam elements was set to be the number of the teeth on the ring gear in order to associate a node with every tooth. The moving load was represented by the dynamic gear mesh forces, which can be obtained from the planetary gear lumped-parameter model. There were two support conditions (uniform supports and pin supports) analysed in this research and ANSYS transient analysis was used to model the dynamic response. In the uniform support condition, it was found that the modulation effect from the carrier arm rotation can be accurately predicted and the vibration spectra matched well with previous publications. In the pin support condition, the spectra from different ring gear rim locations can result in different vibration spectra and it provides a primer guideline for further understanding the effect of the sensor location on the planetary gear vibration monitoring.
Keywords: Finite element analysis; moving load problem; planetary gearbox; vibration spectra.
Lubricated Loaded Tooth Contact Analysis (LLTCA) for Spur Gear Pairs
by Callum Oglieve, Mahdi Mohammadpour, Gajarajan Sivayogan, Homer Rahnejat
Abstract: Gears are key components to the operation of many machines and mechanisms. However, their presence often affects system efficiency and can lead to noise, vibration and harshness (NVH) issues. Therefore, improved efficiency and NVH refinement are the major drivers in the development of gearing systems. These requirements lead to significant efforts expended in the design of optimised gear pairs and their lubrication. Analytical and numerical gear analysis methods are limited to simplified methods such as dry contact conditions, use of basic classical Hertzian contact theory and finite element analysis in tooth contact analysis (TCA). Thus, the generation of more complex models would represent gear interactions, including lubricated contact analysis more realistically.
Tooth Contact Analysis (TCA) is usually the first step for an in-depth; gear efficiency, NVH and durability analysis. Analyses described in open literature study tooth contact neglecting the effect of lubrication. In reality, contact mechanics and lubrication are closely inter-linked, requiring an integrated approach.
This paper outlines a combined FEA-based TCA model with a lubricated contact mechanics analysis for real gear pairs, thus improving the prediction of gear pair efficiency, NVH and durability. An initial dry gear analysis with an estimated constant coefficient of friction in the contact is carried out. The results of this initial analysis provide input data for a subsequent tribological model in order to generate improved estimates of the contact friction for a new TCA. This approach leads to the integration of TCA and lubrication in an iterative manner.
The gear pair geometry is measured using a Coordinate Measuring Machine (CMM) which takes into account manufacturing imperfections and real geometry within its measurement sensitivity of
Keywords: Tooth Contact Analysis (TCA); Lubrication; Tribology; Spur Gear Pair.
Effect of Tooth Profile Modification on the Durability of Planetary Hub Gears
by Ehsan Fatourehchi, Mahdi Mohammadpour, Paul D. King, Homer Rahnejat, Gareth Trimmer
Abstract: Planetary systems offer the advantage of desired speed-torque variation with a lighter, compact and coaxial construction than the traditional gear trains. Frictional losses and Noise, Vibration and Harshness (NVH) refinement are the main concerns. Modification of gear teeth geometry to reduce friction between the mating teeth flanks of vehicular planetary hubs, as well as refining NVH under varying load-speed conditions is one of the remedial actions. However, implementing modifications can result in reduced structural integrity and system durability. Therefore, a contradiction may arise between assuring a high degree of durability and achieving better transmission efficiency, which necessitates detailed system optimisation.
An integrated multi-disciplinary analytical approach, including tribology and sub-surface stress analysis is developed. As a preliminary step, Tooth Contact Analysis (TCA) is performed to obtain contact footprint shape of meshing gear teeth pairs, as well as contact kinematics and applied load distribution. Then, an analytical time-efficient Elastohydrodynamic Lubrication (EHL) analysis of elliptical point contact of crowned spur gear teeth is carried out to observe the effect of gear tip relief modification upon planetary hub sub-surface stresses.
Keywords: Transmission system durability; Gear tooth modification; Planetary wheel hub systems.
Computerised Symbolic Planetary Transmission Modelling for Automotive Design
by C. Spitas, A. Amrin, A. Amani, G. Vasileiou, V. Spitas
Abstract: A method and its computerised implementation is proposed for the modelling of planetary transmission systems. Using a computer symbolic scripting environment, a number of Idea class objects and appropriate methods to manipulate them are defined, implementing all the relationships that govern the system kinematics, mechanical efficiency and geometric compatibility. The outcome is a system of equations involving the most pertinent design and performance parameters, which allow a systematic interrogation of the relationships between system design and performance. This method is particularly useful for the synthesis and design of novel automotive planetary transmissions, where very early in the design process an analytical solution to several inverse problems is required, making the proposed computerised symbolic modelling indispensable.
Keywords: planetary transmission; symbolic modelling; dynamics; efficiency.
Improving strength for automotive plastic gears through directional fibre reinforcement
by Vasileios Spitas
Abstract: In this paper a new topology of reinforcing plastic gears with carbon fibers is introduced. The reinforcement is placed tangentially to the critical cross section at the tooth fillet to improve bending strength. The mechanical modelling of the fibrous reinforcement is performed using an anisotropic material stiffness matrix derived from the analysis of a representative volume element using commercial stress analysis software. Benchmarking against conventional plastic gears illustrates that the maximum fillet stress, which is responsible for tooth failure in overloading conditions is greatly reduced, therefore rendering these gears suitable for considering their use in high load applications such as in the automotive industry. Also the effect of the thickness of the reinforcement on the maximum developed tensile stress at the root is examined. The results show significant decrease of the bending stress at the root fillet rendering this design an alternative way in reinforcing plastic gears.
Keywords: Carbon fibres; gears; plastic; reinforcement; fiber orientation; anisotropic modelling.