Rolling-sliding dynamics and optimization of large-scale cam-roller contacts - Introducing rolling pairs with shifting contact geometry
Pedro Amoroso Feijoo is a PhD student in the department Surface Technology and Tribology. Promotors are prof.dr.ir. M.B. de Rooij from the faculty of Engineering Technology and dr.ir. R.A.J. van Ostayen from Delft University of Technology.
Cam-roller mechanisms serve as mechanical systems designed for the conversion of rotary motion into translating or oscillating motion. These mechanisms are commonly employed in various applications, including small-scale systems like valvetrains and diesel injection pumps for internal combustion engines, as well as large-scale systems such as hydraulic drivetrains (HDs) for offshore wind turbines. Cam-roller follower mechanisms are highly dynamic systems, experiencing varying loads and rapid speed changes. From a tribological standpoint, the cam-roller interface stands out as a crucial lubricated contact where surface damage may occur.
The focus of this Ph.D. project is the study and optimization of cam-roller follower mechanisms such as those used within a novel large-scale hydraulic drivetrain for an offshore wind turbine. The study adopts a systematic approach divided into the following three phases: Understanding, Replicating, and Improving.
Phase One (Understanding), covered in Chapter 3, concerns the development of a modeling framework to assess the rolling-sliding performance of radial and offset roller followers in a large-scale HD. The offset follower configuration is proposed to mitigate the tangential side thrust and enhance the lifespan of the roller runner guides within the cam-roller mechanism. Chapter 3 includes a comprehensive kinematic and force analysis of the cam-roller systems in a large-scale HD, as well as a lubrication and frictional analysis of the cam-roller contact and internal spherical roller bearings. The results provide insights into the occurrence of roller slippage, anticipated traction forces, the influence of roller inertia, and the impact of the frictional torque, among other factors. This analysis contributes to a better understanding of the operational conditions of these contacts, which is essential for progressing to phases two and three.
Phase Two (Replicating), covered in Chapters 4 and 5, is dedicated to the development of an experimental approach and a small-scale test setup to replicate the rolling-sliding dynamics of large-scale cam-roller contacts. Chapter 4 details the development of the test setup and introduces a testing method based on torque control to evaluate the performance of cam-roller interfaces under steady-state conditions. In Chapter 5, the test setup is upgraded, and a method for dynamic testing conditions is developed. In that way, the influence of roller inertia can also be accounted for. The development of the latter dynamic testing technique is crucial as it enables the experimental validation of the modeling framework presented in Chapter 3 and the validation of the improvements presented in Chapter 6. Chapter 5 underscores the need to reduce or eliminate roller slippage to mitigate the potential for surface damage and improve the rolling-sliding dynamics of the cam-roller contact.
Phase Three (Improving), covered in Chapter 6, introduces an innovative rolling pair concept aimed at significantly enhancing the rolling-sliding dynamics of cam-roller contacts by minimizing slippage. The validation of this concept utilizes the experimental techniques and the test setup developed during the previous phases.
Based on the findings of the three research stages outlined previously, the key insights can be summarized as follows:
Chapter 3 shows that the offset follower configuration can reduce the equivalent side thrust by 51%. Additionally, the lubrication and frictional analysis reveal interesting rolling-sliding dynamics. Radial and offset roller followers slip at low loads but slip rapidly vanishes at high loads, causing the emergence of a noticeable peak in the traction force.
Chapters 4 and 5 demonstrate that the custom-built test setup and the experimental techniques introduced adeptly reflect the dynamics predicted in Chapter 3, providing a more manageable and controllable small-scale environment for testing and model validation. The results clearly show that small increments in the resisting torque can greatly increase the slide-to-roll ratios under low loads, heightening undesirable dynamic effects induced by the inertia of the roller and rapid velocity changes.
Finally, the result from Chapter 6 demonstrates that the proposed novel rolling pair design can substantially reduce slippage and mitigate undesired dynamic effects in rolling contacts operating under highly varying synchronous loads, where slippage is an issue. The cam-roller contacts in the HD considered in this study are an excellent example to illustrate the application of this concept.
