Abstract
This study aims to investigate the bearing-free freewheel-clutch and its significant role in structural dynamic effects in e-bike drive units. It hypothesizes that the freewheel's flexibility and a lack of suitable bearings allow rigid body oscillations of the attached gear body which contribute to an overall increase of noise and vibration. As a first step, the method involves a measurement campaign conducted during operation, utilising a specialized test rig that includes torque and rotation sensors and distance-lasers. Combining these results with mathematical operations and direction-dependent forces, the load-dependent and three-dimensional stiffness of the freewheel-clutch is determined. As a second step, it uses dynamic-transient multi-body dynamic simulations to incorporate the gained stiffness as a general force element using spline interpolation and to analyse the system behaviour with subsequent application of frequency response functions and spectrograms. As a result, the determined stiffness reveals a non-linear behaviour, and a frequency calculation indicates that rigid body modes are present up to 5 kHz. Through consideration in the time domain, it can be verified that the system experiences self-excitation solely by varying load, which is independent of the rotational speed, and various resonances occur, especially through a discontinuity of the stiffness curve in the tilting direction. In summary, this study confirms the hypothesis and contributes to an in-depth comprehension that enables enhancing the design of future e-bike drive units.
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