To evaluate the control performance of the PID controller for the cars, a 3D car dynamic model with 8-DOF which can fully reflect the pitch and roll of the car body is proposed in this study. The PID controller is then researched and applied to control the active suspension system of the cars under the different excitations of the road surface and the various car speeds. The control performance for improving the ride comfort of the driver is evaluated via the root-mean-square (RMS) of acceleration responses of the vertical driver's seat, pitching and rolling car body angles. The research results show that the PID controller for the car suspension system have an obvious impact on reducing the vibration and controlling the car body shaking in comparison with the passive suspension system.

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To evaluate the acceleration-frequency characteristics of the suspension system of the heavy vehicles, a nonlinear dynamic model of two-axle heavy vehicles is established. A calculation method based on the complex domain is applied to solve the vibration equations of the heavy vehicle in the frequency domain instead of the traditional time domain. Matlab software is then used to calculate the vibration equations under various operating conditions. The research results show that the resonant frequency of the suspension system is not affected by the vehicle speed and the road surface, while it is clearly influenced by the weight of the vehicle and the stiffness of the suspension system. However, the acceleration-frequency characteristics of the vertical vehicle body, pitching vehicle body, and vertical front/read axles are greatly influenced under various operating conditions, especially at the high speed 30 m.s-1 , a wavelength of the road surface 6 m, and 80 % of the vehicle load.

In order to enhance the ride comfort, stability, and safety of heavy trucks. Based on the dynamic characteristics of the parameters of heavy trucks and its dynamic model, a multi-objective genetic algorithm are developed in the MATLAB environment and applied to optimize the dynamic parameters of vehicles. The weighted root-mean-square (RMS) accelerations of the cab and driver seat vibrations are chosen as the study goals to evaluate the results under different vehicle conditions. The obtained results show that the optimal parameters of vehicles are significantly enhanced the vehicle ride comfort under different operation conditions. Particularly, the weighted RMS accelerations of the awz and awφc are significantly reduced by 26.3 % and 35.3 % under the ISO level B of the road surface, and a vehicle speed region from 17.5 m/s to 20 m/s (63 km/h to 72 km/h).

In this paper, based on the slider-crank-mechanism (SCM) dynamics model, the dynamic parameters of the engine including the eccentricity () between crankshaft centre and cylinder centre of the SCM, the length and radius of the connecting rod and crankshaft, and engine speed are researched on the engine vibration and power, respectively. The dynamic parameters are then optimized based on the multi-objective genetic algorithm developed in MATLAB software to improve the vibration and power of the engine. Both the values of the maximum friction force and maximum torque are chosen as the objective functions. The research results show that the length of the connecting rod (), radius of the crankshaft (), eccentricity , and engine speed () significantly affect the vibration and power of the engine. With the optimized dynamic parameters of 136 mm, 45 mm, 14 mm, and 1850 rpm, the amplitude of oscillation of piston acceleration and the maximum friction force are reduced by 36.3 % and 12.5 % while the maximum torque is increased by 18.6 % in comparison without optimization. Therefore, the vibration and power of the engine are improved.