Vehicles are one of the most common man-made handicrafts. The more comfortable the passenger, the longer run the vehicle. One of the most recent methods employed to reduce vibration levels is the use of springs that not only have the capability of absorbing the latent energy, but also they can convert a large amount of hindering energy into heat. One type them is wire rope spring which look like a power transmission cable. Due to friction between the strands, these springs are capable of decaying and absorbing energy.
In this research, at first, depreciation characteristics of wire rope springs is calculated and analyzed. The springs are modeled in NX software and to study the effect of spring’s spirals on depreciation, three springs with different number of spirals are used. Frictional contacts between the wires as well as static and dynamic analyses are performed using ANSYS software. The results show that Damping ratio of wire rope springs, for low displacement, is more than 0.4, which increases with increasing the number of spring spirals. This feature results in wire rope springs with good energy absorbing ratio in vibrations. These springs have nonlinear stiffness in compressive and tensile loading so that tensile loading increases their stiffness. The stiffness of these springs is linear in shear and roll loading.
In order to investigate the effect of wire rope springs on improving travel comfort features, a quarter car model and also seated seven-degree of freedom driver biodynamic model are used. The results show that, compared to conventional springs, wire rope springs can reduce the maximum acceleration and displacement of the driver's body by 30% and 10%, respectively.

 One of the most updated topics in tracked vehicles is change of vehicle height which is controlled by suspension system. The variation in vehicle height, which causes change in track geometry, affects the vehicle vibrational behaviour. The aim of this study is to develop a parametric computer program to model different tracked vehicle and simulate their motion on an arbitrary terrain profile. This study also investigates the effect of vehicle height on the vibrational behaviour. To do so, constraint equations among different parts of vehicle derived recursively and also equations of motion are formulated according to Newton-Euler equations with help of embedding technique. Besides, for modelling track chain as a closed-loop chain, penalty method has been employed instead of analytical closed-loop equations. To model the contact between the track, wheels and the ground, some algorithms to identify the occurrence of the contact have been presented and the continuous contact force model has been used for the mathematical modelling. The vehicle suspension system has been considered as a coil spring which allows the wheels to move only in the direction perpendicular to the vehicle chassis. The developed computer program with aforementioned specifications is used to investigate the dynamic behaviour of vehicle. The result agrees with the output of RecurDyn multibody dynamic simulations. The vibrational behaviour of the tracked vehicle is also investigated using two different vehicle heights. This reveals that the increase of the vehicle height do not change the frequency. However, it increases the amplitude of vehicle vibration. The ride comfort citeria is also defined and approves that vehicles with lower height are more comfortable than vehicle with higher height. In addition, the vibrational behaviour of tracked vehicles with and without suspension system is compared. It is observed that some of the frequencies in vehicles without suspension system are decreased which fastens the occurrence of resonance due to road conditions. Furthermore, in a simplified model of a track, frequencies and mode shapes are analytically derived (using Eigen-values and Eigen-vectors analysis). These results also show a good agreement with RecurDyn simulation.

This research presents a theoretical study on the elastodynamic response of a high-speed planar crank-slider mechanism. The slider crank is assumed to be formed of a rigid crank, a rigid chassis, a flexible connecting rod and four clearance less bearings. The non-linear equations of motion are obtained by Lagrangian mechanics approach. The partial differential equations of motion simplified to a system of ordinary differential equations using mode summation method. The validity and accuracy of the equations of motion are investigated using MSC.Adams flex toolbox which uses FEM based calculations for dynamic modelling of the flexible mechanisms. To simplify the equations of motion in the present work, the longitudi-nal dynamic behaviour of the flexible connecting rod is neglected. However, under the influence of dynamic forces of the slider the length of the connecting rod can be varied. It is shown that in spite of the simplified and compact form of the equations, the accuracy of the model for high speed dynamic investigations is acceptable. These followed by making the equatons of motion to the dimensionless form and dimensionless parameters of the system are identified. The effect of variation of the dimensionless parameters on the dynamic response of the systems is investigated. To control the vibration of the flexible connecting rod smart material based on the piezoelectric properties is used. Two types of control strategies including conventional PID and Feedback Linearization methods are used to generate the control force. The results show that the Feedback Linearization is more robust against changing of dimensionless parameter compared to the PID, however PID controller has more amplitude divergence rate and shorter settling time.

In this research modeling of the longitudinal dynamics of a passenger car equipped with a variable stroke internal combustion engine has been developed. To drive the variable stroke engine dynamics the mean value method is used. Then the governing equations of motion of torque converter, automatic gear box, the wheel and the vehicle's longitudinal dynamics are derived and followed by modeling in the computer using the Matlab/Simulink software. Since the forward motion of the vehicle is considered, an automatic fuzzy driver is used to command the accelerator (gas) as well as brake pedal during the simulations. Then, to control the engine case tilt angle an optimal linear regulator controller (LQR) as well as a PID controller is employed. To improve the vehicle performance and considering the vehicle speed, the LQR controller determines optimal engine case rotation angle with respect to the driving condition. Comparing the results shows that linear optimal controller is preferred to PID controller. Beside the satisfactory performance of speed error, this controller reduces fuel consumption, especially at high speed. In final part, field test is performed using the LQR controller using a realistic Carsim vehicle model. The results are close with those obtained from the Simulink model.

 In this study, vibration analysis of a tyre with different boundary condition is presented and the effect of adding each condition on the frequencies, is investigated. To see the influence of considering mass of enclosed fluid, the mass of air is added and evently distributed on the elements of inside the tyre. For this aim, the geometry of model is design in the ABAQUS software. A real tyre with model 185/65R14 is provided and cutted to have the correct measure of the section prameters. In this work, the considering components of the tyre are: two belt layers with composite material, one carcass layer, steel angled cords that rebared in the layers, tread and sidewalls that modeled as hyperelastic material. After designing, the frequency analysis is selected to obtain natural frequencies. At the first step of the analysis tyre is in the free boundary condition. In the next step an inflation pressure considering inside the tyre and increase gradually. To see the effect of standing tyre on the ground under its weight, a rigid shell play the role of the ground under tyre. To simulate the weight of the vehicle, a vertical static load applying on the center of the tyre. In the last step a centrifugal force exerting on the tyre as the effect of rotating tyre on the ground. In the all these steps, frequencies obtain and the effect of each step on the frequencies and on the critical speed studied. It is mention that the critical speed occurred when the velocity of the tyre reach to one of the natural frequencies. In the independent chapter, a torus designed and all of the conditions that mentioned for tyre, applying on the torus. The resultes of the torus in the free boundary condition comparing with the analytical solution of the governing equations. Finally observed that by considering internal pressure, applying vertical load and exerting centrifugal force, frequencies of the tire increase. But when the tire standing on the ground frequencies significantly decrease

In this research, the effect of transient behavior of tyre and road on handling performance of a front-wheel-drive (FWD) vehicle is studied. To achieve this goal, a vehicle with 16 degrees of freedom is simulated in Simulink-MATLAB. Then the results compared with those obtained from CARSIM software. This comparison shows that the mathematical model has satisfactory results. In order to study the tyre model exactly, Pacejka steady state model is considered. In this model, dynamic behavior of tyre has been described by both mathematical modelling and experimental data. Since forces in contact patch treat as a dynamic system, all variations in the road conditions excites the system. For modelling these conditions, several types of Transient tyre models as first-order differential equations and second-order differential equation are applied into the vehicle model. Steady state model and transient models are studied for different standard driving maneuvers in which as it expected a remarkable improvement for transient models into steady state model is observed. In addition, to study the vehicle performance, comparison is made between the vehicle and tyre characteristics for steady cornering maneuvers, as well as different conditions (road profile, different friction coefficients, different stiffness coefficients for suspension system and different tyre elasticity). It is shown that the accuracy of the transient models is increased by considering transient factor. Also among all the considered tyre models, the second order model is the best model to take the transient behavior tyre and road into account.

In order to analyze the effect of backlash of drive axle system on the vibrations of the steering wheel in a 16-degree-freedom vehicle model, a shoulder plate steering system, a backlash of drive axle system and Pacejka tires were provided. Furthermore, the backlash between the right and left joint of the drive axle was determined. The torque caused by the impact of the joints was applied as a continuous function of the relative influence of each of the torsional shaft dynamic model. This torque represents the force that is caused by the impact in the clearance between two objects in contact with each other and is perpendicular to the plane of the impact, which is applied to both objects. The torque is introduced by torsional mechanical elements and torsional damper. Having done the modelling and gathering the dynamic and systematic equations and making sure of the selected models, by using MATLAB software and corroborating the results by CARSIM software, it was concluded that the models and their degrees of freedom were chosen and montaged correctly. The results show that increasing or decreasing the size of backlash in the drive axle does not have an increasing or decreasing trend on the steering angle of the front wheels, and it is possible that increasing the backlash for certain parameters could adjust the fluctuations of the steering angle of the front wheels. It is also possible that decreasing the backlash could disturb the angle of the steering. The results also that when the input torque is fixed to both shaft (the car moves with constant velocity) joints, the size of the backlash and the backlash in the shaft between the steering angle does not have any effect on the behavior of the steering angle, and the angle of the steering wheel does not swing. Finally, it was observed that the size of backlash in the joint of drive axle has no impact on the root mean square of vertical velocity of the suspending mass, and according to ISO 2631 the convenience of passengers in the vertical shaft does not depend on the backlash of the drive axle joints.

 The aim of this dissertation is the active static and dynamic balancing of a 6-DOF parallel robot known as Stewart-Gough. For these reasons, first the static and dynamic equations of the robot are derived and then the equations are modified for static balancing using the counter weights and pantograph method. In order to achieve the dynamic balancing, four Control Moment Gyro with pyramidical structure are mounted on the moving platform. To show the effect of the actuators and validate the derived equations, the mechanism is modeled and simulated using Matlab-Simulink programming. Furthermore, to validate the result another simulation with same parameters is implemented in MSC-ADAMS. Finally, the Linear Quadratic Tracking method and the gain scheduling technique are adopted to control the actuators. The simulation results show that the controller suppresses all of the actuators forces in the static conditions. Also, the results show satisfactory control over the unbalancing torques that applied to the fixed base.

 In this study, an optimal control system that has been designed on the bases of a brake force distribution on the wheels of a long combination vehicle, to achieve lateral stability at high speeds have been investigated. For this purpose a vehicle which is composed of a tractor and two semi trailer, with 12 degrees of freedom in Matlab-Simulink software has been modeled. For validation of the model listed, Simulink model simulation results with the results of the Trucksim vehicle model while the vehicle is crossing a double lane change maneuver with the initial speed of 88 km per hour, are compared. As the vehicle passes through the maneuver it becomes to be instability in lateral dynamics and making tail swing movements, Thus a fuzzy control system based on ESC method for controlling the yaw rate of each vehicle is designed. The system works by sending the appropriate braking force to the appropriate wheel of the vehicle, so it controls the over steer and under steer of the vehicle. After of designing of the fuzzy controller, 38 variable in the controller with the method of effective manager optimization, have been optimized. The results of applying the controler to the vehicle, indicates not only decreasing of yaw rate of each unit but also closeing the vehicle yaw rate graph changes, to yaw rate changes of the reference model in each unit, and also considerable reduction in RWA benchmark has been achieved.

<p>In this thesis, nonlinear dynamic behavior of a suspension system including progressive springs as well as effect of progressive springs on ride performance is investigated. The study is started with mathematical modelling of the progressive spring. Then the phase portrait of sprung mass system is demonstrated. To validate the mathematically introduced model of double wishbone suspension system, the computer models are built in two packages Simulink-MATLAB and Msc Adams. In the next step, the ride comfort quality of the progressive spring assisted vehicle is compared with that of assisted with regular spring. According to the results the progressive springs improves the ride quality. In addition, an investigation is performed on finding a coil spacing arrangement to achieve the best simultaneously ride and stability performances. In the final part, perturbation method is used to determine the nonlinear vibration characteristics of the vertical dynamic of the vehicle. A comparison between the analytical results with the exact solutions show the accuracy of the closed form derived solutions.</p>