Researches On Driver's Seat Suspension System Of Off-Road Vehicles Based On Magnetic Spring

Researches show that it is the simplest, directest and most economic method utilizingseat suspension to improve the ride comfort for the off-road vehicles such as agriculturaland forestry machinery, construction and quarrying vehicles and machinery etc., whichcommonly work and run in worse environment. Therefore carrying out an in-depth studyon the driver's seat suspension system and taking feasible technical measurements toisolate the vibration transmitting from the vehicle bottom to human body through thevehicle chassis and the seat is an important and practical subject for improving the ridecomfort of off-road vehicles.Based on the requirements of the off-road vehicles for the driver's seat suspension, thenowaday study actualities of driver's seat suspension system home and abroad and theadjustability and controllability of the magnetic spring stiffness, a kind of mingledsingle-direction magnetic spring composed of electromagnet and permanent magnet wasadded to a scissors linkage seat suspension to establish the driver's seat suspension whosevertical equivalent stiffness is non-linear and can be controlled. The finished work andachieved results are generalized as follows:1. Researches of the static and dynamic characteristics of the scissors linkage seatsuspension. One kind of scissors linkage seat suspension was chosen as the structural baseof the magnetic force seat suspension and the complete and systematical study about itsstatic and dynamic characteristics and their effect factors was made through theoreticalanalysis, dynamical simulation and experiment. Study results show that the seat suspensionsystem can be approximately treated as a linear system and its vertical equivalent stiffnessis almost unchanged in the working stroke; the spring layout mode, suspension geometryparameters and the spring stiffness all affect the seat suspension vertical equivalentstiffness in some degree; the natural frequency, damping ratio, dynamic amplificationfactor and the acceleration root of mean squares of the seat suspension are all related to theequivalent sprung mass. Moreover, the effect degree of the mass on the dynamicamplification factor is related to the damping coefficient of the damper; because of thefriction between motion parts and the gravity and rotary inertia of the scissors linkages the seat suspension appears "locked" when the excitation frequency is low and the magnitudeis small. The peak value frequency of the dynamic amplification factor in experiment isbigger than the theory and simulation results and it obviously decreases with the excitationmagnitude increasing.2. Researches on the stiffness adjustability of the scissors linkage seat suspension withadditional elastic part. First the layout mode of the additional elastic part in the scissorslinkage seat suspension was theoretically analyzed and then the theoretical model of theseat suspension with additional elastic part was established. Based on the theoretical modelthe effect of the additional elastic part on the characteristic relationship, the seat verticalequivalent stiffness and the suspension vibration natural frequency were analyzed and thefeasibility of changing vertical equivalent stiffness by adjusting the stiffness of theadditional elastic part was discussed, which will build theoretical base for the constructionof the magnetic force seat suspension whose vertical equivalent stiffness is adjustable.Research results show that the relationship between the vertical load and displacement ofthe seat suspension with the additional elastic part behaves nonlinearity and thenonlinearity becomes stronger with the stiffness of additional elastic part increasing; theseat suspension vertical equivalent stiffness and the vibration natural frequency havedifferent values in different suspension position and their values in the suspensionextending stroke are much larger than which in compressing stroke; the stiffness of theadditional elastic part has obvious effect on the characteristic relationship, the verticalequivalent stiffness and the suspension vibration natural frequency.3. Construction of the magnetic spring and theoretical analysis of its magnetic field.Systematical analysis and calculation were made on the main design parameters of theadditional elastic part with adjustable stiffness—the mingled single-direction magneticspring, and the contents included calculation of the magnetic field force and the working airgap required by the magnetic spring, choice of the material and the working parameters ofthe electromagnet and the permanent magnet and determination of the geometry parametersof the magnets. In addition, the formulation of the air gap magnetic flux density and theaxial magnetic field force were deduced according to the theory of static electrics andelectrodynamics and their effecting factors were analyzed, which are theoretical guide forthe experimental study of the magnetic spring. Research results show that the air gapmagnetic flux density of the magnetic spring is related not only to the electromagnetismwinding current, the diameter and length of the permanent magnetic and the working air gap but also to many other factors such as the circles, length and thickness of theelectromagnetism winding, the length of the iron core and the demagnetizing factor etc.;the axial magnetic field force of the magnetic spring is mainly decided by the axial andradial magnetic flux density on the plane z_m in the air gap and the diameter of the facedmagnet, and the position of the plane z_m is decided by the magnetic flux density in the airgap produced by the magnets.4. Experimental study on the magnetic spring. The space distribution of the magneticflux density of the electromagnet with different magnetic pole shape under differentelectromagnetism winding voltage and that of the permanent magnet with differentdimension were experimentally studied; the experimental system for magnetic forcecharacteristics test of magnet spring was Constructed and the effecting factors of themagnetic force characteristics such as electromagnetism winding voltage, permanentmagnet dimension and the combination of different permanent magnet 1 and 2 wereexperimentally studied. Research results show that the average air gap magnetic fluxdensity of the electromagnet with flat magnetic pole without cap is larger than that of theother two magnetic poles; the surface and air gap magnetic flux density of permanentmagnet is decided by its ratio of length to diameter; For the repulsive type magnetic spring,when the surface magnetic flux density values of the two faced magnetic poles have bigdisparity and the air gap is small to some degree the repulsive force will decrease with theair gap decreasing and the magnetic spring stiffness behaves negative stiffness; and whenthe surface magnetic flux density values of the two faced magnetic poles are nearly samethe repulsive force will increase with the air gap decreasing; with the electromagnetismwinding voltage increasing the axial magnetic force increases linearly and the magneticforce characteristic curves move up along the force axis; moreover the curvature of thecharacteristic curves also increase with the electromagnetism winding voltage increasing.5. Development and experimental study of the magnetic force seat suspension. Themagnetic force seat suspension system was developed and its vertical equivalent stiffnessconstitution was theoretically analyzed; the experimental system for the magnetic force seatstudy was established and the dynamic characteristics of the magnetic force seat suspensionwere experimentally studied. Research results show that the dynamic amplification factorof the magnetic force seat suspension decreases with the electromagnetism winding voltageincreasing and increases with the equivalent sprung mass increasing in thevibration-amplifying zone and in the vibration-isolating zone it decreases with the equivalent sprung mass increasing and nearly have no relation with the change of thevoltage; the peak value frequency of the dynamic amplification factor and the respondingacceleration r.m.s, both increase with the electromagnetism winding voltage increasing anddecrease with the equivalent sprung mass increasing; compared with the magnetic forceseat suspension with damper the peak value frequency of the dynamic amplification factorand the responding acceleration r.m.s, of the magnetic force seat suspension withoutdamper are both lower and the degree of the equivalent sprung mass effecting on them issmaller.It is expected to build theoretical base and technological support for the in-depth studyof the semi-active seat suspension that is based on the magnetic spring and whoserelationship between vertical load and displacement behaves nonlinearity and the verticalequivalent stiffness can be adjustable.