Efficiency and losses of bi-directional, non-back-drivable roller clutches

Abstract

Non-back-drivable clutches represent an efficient alternative to low-pitch-angle lead screws and worm gears to achieve non-back-drivable drivetrains. To cement their usefulness as high-efficiency solutions, this paper presents an investigation into the internal behavior and losses of these clutches, leading to the development of a dedicated, physics-based model for predicting clutch efficiency. The analysis identifies five distinct operating configurations of the clutch depending on its speed. By characterizing the frictional behavior within these configurations and the transitions between them, a predictive model is built to estimate power losses and efficiency across the entire operating range. The proposed model was compared to experimental results under a load of 1.45 Nm at 50 rpm and under no-load conditions up to 2000 rpm, achieving a normalized root mean square error below 15%. Furthermore, the study demonstrates that roller clutches can achieve high efficiency on a wide range of operating points, with measured efficiency of 96% at 40 rpm and 1.45 Nm (with losses of 0.23 W) and no-load losses of 46 W at 2000 rpm.