Vehicle vibration analysis

Abstract

Engine noise and vibration harshness is a big concern in the competitive automotive vehicle manufacturing industry. It is very important to limit the vibration and noise levels for the general pleasure of driving. Vibration could cause human discomfort as experienced by the vehicle driver and the passengers. Vibration transmitted from the engine to the vehicle's support structure is also a disadvantage from a material fatigue point of view. For this literature survey done, no previous work could be found where a vibration absorber was used at an engine of a vehicle. The feasibility of an engine vibration absorber to reduce vibration levels at a vehicle for several driving conditions was examined in this study. An Engine Vibration Absorber was successfully designed, manufactured and also experimentally characterised and evaluated. The design involved the development of mathematical models to determine mainly responses and natural frequencies. The mathematical models were implemented in computer programs developed. The design included the choices that were made regarding size, layout, position, mass, stiffness and damping properties for this Absorber. All the parameters required as input data for the computer programs were experimentally characterised. The dynamic properties of rubber mounts used at the Absorber were amplitude excitation dependant and thus complicated the analysis and the characterisation, but these stiffness and damping magnitudes were successfully determined and used in the computer simulations. The Engine Vibration Absorber was successfully tuned for a frequency that corresponded to the vertical bounce mode natural frequency of the Engine mount system. The predicted and measured natural frequency magnitudes of the two-degreeof- freedom system were compared. As criteria of vibration transmitted, the dynamic force magnitudes transmitted through the Engine mounts to the vehicle's support structure were computed with the programs developed. These dynamic force magnitudes transmitted were also experimentally determined. These predicted and measured dynamic force magnitudes were compared for several operational conditions. Various operational conditions were theoretically and experimentally investigated. Steady state conditions included responses from road input forces, as well as from internal engine shaking forces. Transient conditions included responses resulting from road impact forces, engine starting, and engine stopping conditions. The study shows that the Engine Vibration Absorber reduced the noise levels measured inside the vehicle's compartment. The Engine Vibration Absorber very effectively reduced the dynamic force magnitudes (vibration) transmitted to the vehicle's support structure for all the different road input conditions at or near resonance. The Engine Vibration Absorber significantly reduced the significantly larger vibration amplitudes caused by road inputs, but with no significant negative effect regarding any additional dynamic forces transmitted when the Engine was running at several speeds.