| Off-road vehicles work in mines, construction sites and other harsh environments.Due to the poor road surface, complex working conditions and the driveline vibrationof vehicle itself and so on, the drivers suffer severe whole-body low-frequencyvibration.This can lead to a variety of occupational diseases, such as cervical vertebraaches, low back pain, etc., which will harm the drivers’ physical and mental, and evencan cause the driver to lose the ability to work, and then result in the productionefficiency decline in mining and construction sites. Thus it will seriously affect theeconomic benefit both in mining and construction sites. In addition, the treatments forthe above-mentioned related diseases can also cause huge economic losses. Therefore,it is very urgent to carry out researches on the vibration comfort for off-road vehicles.Off-road vehicle’s seat is a key link on the vibration transmission path, which directlycontacts with the driver in a large area, and changing seat parameters appropriately,has little effect on vehicle’s performance. Therefore, the study on the off-roadvehicle’s seat has attracted more attentions of researchers. Suspension is the majorcomponent of off-road vehicle’s seat and plays a decisive role on the vibrationcomfort of seat. Mostly existing seat suspensions are designed based on the theory oflinear vibration isolation, while isolation effect for the theory of linear vibration isrelative poorer for the low-frequency vibration. Therefore, the nonlinear theory isintroduced to study the characteristics for the off-road vehicle’s seat suspension in thispaper. The paper is completed supported by the National Natural Science Fund Project(51175216). The static characteristics, displacement transmissibility, sub harmonicresponse characteristic of off-road vehicle’s seat and dynamic characteristic ofoff-road vehicle’s seat-man system are studied systematically in the paper. Also, theseat nonlinear suspension is innovative designed based on the theories of this paper.Then the static characteristic test and vibration isolation performance test are carriedout. The main work and conclusions of this paper are as follows:(1) Static characteristic of seat nonlinear suspension. The mathematic model ofstatic characteristic of nonlinear suspension of off-road vehicle’s seat is establishedand verified by the simulation using the ADAMS software. And then the impacts of main design parameters of the nonlinear suspension on the static characteristic arediscussed using the mathematic model. It is found that the desired zero stiffnesscharacteristic, arbitrary linear stiffness, and nonlinear stiffness characteristic with thezero or positive minimal stiffness can be achieved through reasonably matching thekey design parameters. And the suspension vibration isolation performance can makeadjustment with the driver weight by changing the pre-compression of the main spring.The simplified mathematic formula for static characteristic of the nonlinearsuspension of off-road vehicle’s seat is provided, and the basis of mutual matchingbetween stiffness and damping is proposed by analysis.(2) Displacement transmissibility characteristic of seat nonlinear suspension.Mathematic models of displacement transmissibility characteristic of the seatnonlinear suspension of off-road vehicle, which the minimum stiffness is zero andpositive, are derived based on harmonic balance method. And the numericalverification is made by fourth-order Runge-Kutta method. Then the impacts of keydesign parameters on the displacement transmissibility of seat nonlinear suspensionare analyzed. It is found that the vibration isolation frequency band of nonlinearsuspension can be widened through rational matching key parameters and even theentire displacement transmissibility can be less than1. In addition, it is found that thesteady vibration position deviate from the equilibrium position, the comparison andanalysis on the characteristics between linear and nonlinear seat suspension is carriedout.(3) Sub harmonic response characteristic analysis on seat nonlinear suspension.The second-order approximate analytical solution of time domain displacementresponse of single degree of freedom vibration model of seat nonlinear suspension ofoff-road vehicle is derived based on multi-scale method. And the frequencycomponents of sub harmonic response is analyzed based on the approximateanalytical solution. In addition, the numerical solution is conducted using MATLABsoftware and the time domain displacement response curves are obtained. Then thefrequency components are analyzed using FFT method on the time domain curve.Research results show that the displacement response mainly consists of harmonicresponse, and the proportion of sub harmonic component is nearly zero in theachievable parameters for the seat nonlinear suspension.(4) Dynamic characteristic of off-road vehicle seat-man system. In the paper,8 degrees of freedom dynamic model of off-road vehicle seat-man system is established,and the harmonic excitation, multi-frequency combination excitation, randomexcitation and impact excitation are modeled. The seat-man dynamic model and theexcitation model are coupled and solved using the fourth-order Runge-Kutta method,then the dynamic characteristics of off-road vehicle seat-man system is discussed.Analysis results show that the stiffness and damping of seat have serious impact onthe dynamic characteristics of the seat-man system compared with other seatparameters.(5) Innovative design and test of seat nonlinear suspension and nonlinearvibration isolator. Two nonlinear suspension of off-road vehicle seat and a nonlinearvibration isolator are innovative designed in the paper. Test content includequasi-static test and vibration test. Test results indicate that the theory provided in thepaper is correct.Design theory and new suspension proposed by this paper are important toreduce the transmission of vibration to the driver, and to improve off-road vehiclevibrition comfort. |
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