Assignment on Vehicle Vibration Analysis

Added on - 21 Apr 2020

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SOLUTIONS TO THE QUESTIONSQN 1) Vehicle VibrationVehicle vibration is normally caused by the ground interaction with road roughness, forcedynamics, unbalanced wheels, and/or engine problems. Vehicle vibration has become a criticaldesign issue that Mechanical Engineers in the Auto-industry are increasingly undertakingresearch to succinctly uncover the phenomenon.However, firstly, we define the following terms:Modes- or simply stated as mode of vibration refers to the finite ways in which vibration in abody can occur. Each way of vibration will have a distinct frequency range and amplitude.Complex objects can pose great difficulty in accurately determining the characteristics of thevibration modes. However, in vibration analysis, there are techniques that can be used toinfinitesimally link the theory to the actual performance (in terms of vibration).Eigen values-These are special sets of scalars that are normally linked with a system of linearequations. To demonstrate this, Wolfram (2017) gives the following mathematical definition:Firstly, let A be a linear transformation represented by a matrix A’ such that:Ax’= λx’...(i)Where λ is the eigen value and x’ is the eigen vectorEigen vectors and values are significant in the analysis of mechanical vibrations where thesolutions obtained are used to represent the state space of the system, a process known as matrixdiagonalization (Wolfram, 2017)Eigen vectors- This is a paired correspondence of the eigen values hence the eigen vectors areoften accompanied by the eigen values as shown in equation (i)Now, we get back to Vehicle vibration. Notably, vehicle vibration can never be covered withoutan in-depth look at the major causes of this phenomenon hence the following are the majorcauses of vehicle vibration (as mentioned earlier):(i)Engine ProblemsThe engine normally has reciprocating and rotating components. Due to unbalancedforces, motion of these components can sometimes be a major cause of enginevibrations. Although designers have integrated some mechanical means to restrict thedegrees of freedom, failures in engine firing and reciprocating parts unbalances areoften combined to produce a complex source of vibration which varies with engineoperating conditions. Additionally, the transmission shaft and crank shaft normallyhave mountings on them such as couplings. The centre of gravity of these shafts lies
somewhere in the middle such that during rotational movements, the shafts wouldexperience centrifugal force. If these forces are not balanced, then the shafts wouldbegin wobbling and further increasing the engine vibration.(ii)Road surface roughnessThe roughness of road surface is another contributor to vehicle vibrations. As the carmoves along, the tires interact with the surface such that up and downward motionoccur in a repetitive fashion. Although the suspension springs are designed to absorbthese vibration shocks, a poorly designed suspension would allow transmission to thepassenger couches hence causing greater discomfort. To overcome this, thepredisposing surface conditions are normally taken into account so that we end upwith vehicles that can actually surmount the rugged terrain with just a little amount ofdiscomfort at play.(iii)Force dynamicsA balanced state of force systems in the car is one way of ensuring that car vibrationis brought under control. The car suspension system and the chassis design wouldcome in handy in this case. However, should this not be done properly then forcebalance in the car could be far-fetched. As a result of this, the test engineers mustalways perform rigorous tests to check on the car mechanics both in motion andstationary state.(iv)Unbalanced wheelsUnbalanced wheels normally cause uneven rotation of the wheels so that a rotation ofall the wheels is not synchronized. This may result into serious problems such asloosening of bolts and nuts. Therefore, if this is unchecked then it can lead to fatalinjuries especially when car is moving at high speed.In conclusion, vehicle vibration need not be trivialized as it has proven detrimental tothe health of the passengers. It can lead to driver fatigue as prolonged exposurecauses the muscles to be less responsive hence characteristically drowsiness wouldoften set in. It can also make the occupant safety to be at stake as vibration is likely tocause accidental disassembly of bolted components such as the wheel and axle.Unfortunately, during high speed drives, the probability of fatal injuries due toprolonged vibration would be higher.However, as mentioned earlier, engineers have come up with sophisticated tools andmethodologies to detect and measure the levels of vibration in the car body. According toPopović & Matijević (2016) one of these critical whole-body vibration tests is the bump test.This test can be envisaged as one in which a hummer hits an object and the whole objectvibrates. The resulting frequency is measured and cross checked to ascertain that it is within the
safe range. A series of bump tests are done and in the process the resonance frequency can bemeasured. However, engine vibrations can be minimized incorporating viscoelastic materialswith a higher damping factor. Notably, mechanical system models have been designed to aid inunderstanding how engine vibrations occur so that reduction techniques can be integrated in thedesign. For instance, as argued by Deulgaonkar, Kallurkar & Mattani (2016), constrained layerdamping has successfully been applied in the engine design to limit the excessive vibrations.Additionally, tuned viscoelastic damping seems to register more positive results than theconstrained layer damping.Furthermore, there has been advancement in analytical tools; which are normally applied toderive an ideal vibratory system. The resulting models are then used to uncover the performancecharacteristics of the said system. Admittedly, Design Engineers would often rely on thesescientific findings and sometimes even form part of the teams to explore these phenomena sothat in the next design phase, a more superior product would result. Transfer Path Analysis isamong the analytical techniques that are often applied in these vibration scenarios (Popović &Matijević , 2016) . The method would enable identification of the paths relative to the totalvibration produced by the whole body. In fact, its functionality can be extended to includeanalysis of engine noise, vibration and harshness (NVH). It enables tracing of the vibrations rightfrom its source (perhaps the engine) down to the transmission (the gears and gearbox) and finallyto the passenger seat. These are then summed up by picking on the individual forces andvibrations. Therefore, this would allow complex vibratory systems to be modeledand analyzedeasily. However, there are limitations with the method as it cannot exhaustively identify all thevibration hotspots and singularize them; it is practically impossible to do this with the technique.In conclusion, therefore, vehicle vibration still presents an interesting arena for researchengineers and scientists do explore further. But what is encouraging is that their efforts arecausing further advancement in the vehicle vibration control technologies.QN 2) Passenger comfort and ride qualityPassenger comfort and ride quality are often two critical parameters that enhances acceptancefrom customers and ultimately lead to repeat purchases on the side of the buyers (Shirahatt, A,Prasad, P & Panzade, P. (2 008). The entire design of the vehicle greatly determines theperformance levels of these two factors. Many a research engineers have attempted to studydifferent vehicle models with the aim of establishing the degree of comfort and ride quality inthose automobiles. This section will focus on such design factors that can affect the comfort andride quality of the vehicle. Notably, central to this is the engine design.In the engine, where masses spin, rotate and reciprocate at menacingly higher speeds, coupledwith out-of-balance mechanisms, it is inevitable for the car to remain smooth in motion.However, inasmuch as engineers do attempt to deaden the engine vibration, passengers are stilllikely to be affected by discomfort arising from the engine motion. However, there are
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