Assessing the Vibration Fatigue Life of Engine Mounted Components

Abstract

As part of the design validation of components mounted on rotating machinery such as a car engine, it is essential to understand the environmental stress in which they operate. In the case of vibration loadings, the reliability must be verified according to accelerated tests that realistically reproduce the in-service stress. Indeed, a representative validation profile permits not only the assessment of the component durability, but also provides a reliable reference for design optimization (downsizing), reducing development cycle costs, and time scale. This paper proposes an innovative methodology to generate tailored vibration signals more representative of the real environment. First, the severity of the test is tailored to the specific engine usage profile, i.e., the time spent at each revolution per minute (RPM) for a given percentile of customer usage. Traditional signals of Power Spectrum Density (PSD) and sine sweep are developed according a fatigue damage approach (test tailoring). Then, a more representative vibration specification is obtained as a multiple-sine-on-random signal. The signal is expressed as a series of multiple sine sweeps (representing the engine harmonics) and a PSD (representing the random leftover signal). A case study applied to an engine mounted heat exchanger (a water-cooled intercooler) is presented. The generated specification is compared to the validation signals developed according to existing procedures. The results show that 1) the tailored approach decreases the risk of unnecessary over-testing and 2) the multi-swept-sine-on-random signal guarantees the best representativeness of the real environment.

A Novel Engine Vibration Measurement System based on the MEMS Sensor

“…Today, many engine designs are out of preference because they create more noise and vibration than their competitors during normal operation. The general cause of vibrations during the operation of an internal combustion engine is the change in in-cylinder pressure, the noise created by the lubrication gaps between the components, the piston moving up and down, the crank-connecting rod mechanism gaps to which it is connected, and the axial travel gaps in the parts [1,2]. These vibrations of the engine can be described as typical nonstationary motion [3].…”

“…In another study, in which the effects of fuel and oil used in the engine on vibrations were examined, it was observed that the vibrations that occurred during the tests were analysed with two 3-axis accelerometers placed on the crankshaft main bearings [6]. In the literature, it has been determined that the vibration intensity of the engine increases with increasing engine speed and load [2,[6][7][8][9].…”