Simplified models for mechanical transmission efficiency with opposing and aiding loads

The computational power available for design of complex equipment is steadily increasing, allowing the use of very detailed models of the physical behaviour of the system. Nevertheless, in some situations simpler models are required. This is the case of preliminary sizing, when most of the system architecture is still to be defined in detail, and of monitoring routines intended to run in real-time, possibly with limited hardware resources available on-board a vehicle or embedded in equipment. With the emerging application of Prognostics and Health Management (PHM) to system design and development, simplified models of mechanical, hydraulic and electric equipment are becoming a key element to enable the implementation of fast and reliable algorithms for fault detection and estimation of remaining useful life. In this context, we address in particular the modelling of friction for mechanical parts. Variations from the nominal value of dry friction are usually among the early effects of wear and degradation of components: for example, a surface damage on a moving part can lead to an increase of the friction value, while the wear of a preloaded sealing can result in reduction in friction. Hence, in this work, we aim to develop accurate yet simple models for the efficiency of mechanical transmissions, which can be used within system level simulations intended to run in real-time for prognostic and monitoring tasks.