Design and evaluation of a lightweight automotive crank mechanism with integrated vibration damping

Thesis Abstract

This study addresses the persistent issue of excessive vibrations and weight penalties in automotive crank mechanisms, which compromise energy efficiency, component longevity, and ride comfort. The research targets the design and evaluation of a lightweight crank mechanism with an integrated vibration damping system to reduce engine-induced excitations while maintaining structural integrity and manufacturability. The aim is to deliver a validated design that achieves at least 15% reduction in peak vibration transmissibility and a 12% mass savings relative to conventional crank assemblies, without compromising peak torque transmission or durability. Specific objectives include (i) developing a consolidated design framework for a lightweight crank with embedded damping features, (ii) conducting finite element analyses to optimize stiffness distribution and damping element placement, (iii) prototyping a representative crank module and validating its dynamic performance under simulated engine operating conditions, (iv) experimentally evaluating vibration attenuation, wear, and thermal behavior across representative loading scenarios, and (v) performing a comparative life-cycle assessment to quantify potential gains in fuel efficiency and maintenance costs. A mixed-methods approach is employed. The research adopts a design-oriented engineering methodology combining computational and experimental techniques. The population comprises crank assemblies used in small to mid-size internal combustion engines, with a purposive sample of three geometries conventional, semi-structured lattice, and fully embedded damping cranks. A total of 18 dynamically loaded crank samples are subjected to modal and transient dynamic tests on a multi-axis test rig under simulated engine speeds ranging from 1,000 to 6,000 rpm. Data collection integrates high-frequency accelerometers (?20 kHz), strain gauges, and a torque sensor suite to capture modal characteristics, peak responses, and energy dissipation. Finite element analyses are performed in ANSYS Workbench to optimize cross-sectional geometry and damping element placement, while a reduced-order model (ROM) based on Craig-Bampton reduction informs real-time dynamic predictions. Experimental investigations include sine sweep, random vibration, and transient crankshaft torque tests. Statistical analyses comprise ANOVA to compare vibration metrics across designs, regression analysis to relate damping element properties to attenuation, and response surface methodology (RSM) to identify optimal combinations of mass, stiffness, and damping. Key expected findings include a demonstrable reduction in global vibration transmission at critical engine excitation frequencies, with the embedded damping crank showing up to a 20% decrease in transmitted RMS acceleration at the piston-crank interface and a 12–15% improvement in bending stiffness-to-weight ratio. The study anticipates confirming that a strategically placed viscoelastic damping layer within the crank web and a segmented stiffened lattice collar can achieve significant mass reduction without sacrificing fatigue life. Complementary results from modal testing are expected to reveal a favorable shift in natural frequencies away from dominant engine harmonics, reducing resonance risks. The ROM-based predictions are projected to align with full-scale experiments within ±8% across key metrics. Contributions to knowledge include a novel integrated damping-crank design paradigm linking lattice-inspired lightweighting with embedded viscoelastic modal damping, validated through a rigorous experimental workflow and high-fidelity simulations. The research advances understanding of how integrated damping modifies dynamic stress distributions, informs manufacturing feasibility for additive and conventional processes, and provides a scalable design methodology for next-generation engine architectures. The study offers practical implications for improving fuel efficiency through reduced engine vibration losses, extending component life by mitigating fatigue damage, and enabling more compact engine configurations. The main conclusion posits that an integrated damping crank with a lattice-based lightweight core can achieve meaningful vibration suppression while preserving or enhancing mechanical performance. Recommendations include extending the approach to high-performance engines, exploring active damping augmentation for transient load scenarios, and pursuing collaborative industry validation to assess long-term reliability and manufacturability at scale.