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Vibration isolation for a passenger's seat in a Mobile vehicle using active and semi-active Dampers

Rajendra, Beedu (2007) Vibration isolation for a passenger's seat in a Mobile vehicle using active and semi-active Dampers. Phd. Thesis thesis, Manipal Institute of Technology, Manipal University, Manipal.

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Abstract

Perceived comfort level and ride stability are the two most important factors in the evaluation of passenger's seat in a mobile vehicle. There are many aspects of vehicle that influence these properties, most importantly the primary suspension components, which isolate the vibration. from the axel of the vehicle to the chassis. In the design of conventional primary suspension system there is a compromise between the two quantities of comfort and vehicle stability. Low damping gives ride comfort whereas high damping provides. better vehicle stability. In a passive suspension system the characteristics of the components such as spring and damper are fixed. These characteristics are determined by the suspension designer according to the intended application. The parameters of passive suspension are fixed to achieve certain level of compromise between reducing the vibration and increasing the road holding i._~'"".ftadjustable suspension system with a variable damper characteristic iele body and seat provides better performance in terms of stability of the passenger. A suspension system between the seat -tv-hicle body is called secondary suspension system. In the view of using e I semi-active with adjustable damping coefficient suspension system, an attempt has been made in this thesis to design and develop a variable damping coefficient hydraulic damper, which can be used as an active or semi-active damper and an eddy current damper which acts as active suspension system which is very useful for fine turning of the vibration isolation of the suspension system. The basic principle of newly designed hydraulic damper is same as that of existing hydraulic damper used in the primary suspension systems. In this case, a variable pilot valve is provided in the piston rod. The lubricant can flow from one chamber to another of the cylinder as the piston moves to and fro. The restriction to the flow is controlled by the pilot valve, which can be activated externally. Using the continuity and momentum equations the fluid flow pattern is studied and relevant equation for the damping coefficient is derived for different steps of valve openings. After determination of the parameters of hydraulic damper to meet the given specifications, a simple computer program was developed and a model was fabricated in the laboratory. To obtain the transient response of the hydraulic damper, a swing type carriage is designed so that the damper with the carriage oscillates with the help of spring mass system. For different pilot valve openings of the semi-active hydraulic damper, transient responses were recorded for a step input using piezo-electric accelerometer pickup and data acquisition system. The ~ corded data was further analyzed for presentation using LabVIEW and ORIGIN 6 softwares. The damping coefficients obtained by impulse, step and i u80idal force inputs are closely in agreement with the theoretically computed damping coefficient. In this thesis report, an attempt has also been made to tudy the feasibility of eddy current damping for the vibration isolation pIa1tfonm.Commonly, passive and semi-active dampers are used in owever, their characteristics are fixed. Since the damping CJ8Ilnot be varied in the passive dampers, many researchers have active vibration isolation system using electro rheological fluid or 1810 rheological fluid. Eddy current effects are used for braking purpose d researchers have reported the use of eddy current brakes. However, till today there is no work carried on eddy current damping for vibration isolation. A two degrees of freedom vibration system is visualized to isolate the vibration of one of the masses using eddy current damper. An experimental two degrees of freedom vibration system was fabricated in the laboratory. Electromagnets are mounted on the. base platform mass with an air gap. Second mass is mounted on the base platform through a spring with an aluminium plate at its bottom. Aluminium plate is freely allowed to move in the air gap of the electromagnet. Depending on the magnetic flux produced in the electromagnet due to electric current, the eddy current damping effect can be varied. Thus for different amplitudes of vibration the second mass can be brought to constant amount of amplitude of vibration by providing a variable damping. Theoretical flux density is computed from basic equations and is correlated with experimental value. A Hall effect gauss meter is used to measure the magnetic flux. The relevant equations to compute damping coefficient due to eddy current effect are derived and computed values of damping coefficient for different current and thickness of the eddy current plate were verified with experimental results. The experiments were conducted and transient behavior of the mass was recorded using a piezoelectric type accelerometer and data logger system. Using the logarithmic decrement method damping coefficients were computed for different values of current and different eddy current plate thickness. Experimental results are closely in agreement with theoretically computed results The extension of the work for two dimensional damping of a passenger's seat is carried out using hydraulic and eddy current dampers simultaneously. A special seat arrangement is visualized to control the v rtiesl and horizontal vibration of the passenger's seat. The high frequency tion forces are damped through variable semi-active hydraulic damper and fine tuning of low frequency vibration forces is achieved through eddy current damper to provide more comfort. An experimental set up of seat arrangement is fabricated in the laboratory. Seat arrangement is subjected to various types of the tests such as impulse test and multi-mode vibration test. The results obtained through the tests are analyzed and presented. For multimode vibration test, five electric motors with eccentric masses are mounted on the platform of the seat assembly and analyzed for different operating frequency. The results obtained from the experiments of the seat set up are presented graphically.

Item Type: Thesis (Phd. Thesis)
Subjects: Engineering > MIT Manipal > Mechanical and Manufacturing
Depositing User: MIT Library
Date Deposited: 15 Dec 2014 11:09
Last Modified: 07 Sep 2015 09:38
URI: http://eprints.manipal.edu/id/eprint/141252

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