Study On Designing Validation And Simulating Optimization Of New-Style Self-Centering Devices For Vehicle Suspension Height

The main benefits by adopting a suspension height self-centering device have been proved in practice for many years, i.e., suspension performances can be significantly improved and component lifespan can be prolonged. Besides, the self-centering device for vehicle body height can maintain proper body attitude along with the function of self-aligning for headlights,and the self-centering device for seat height can keep steady seat height and provide good visual scope and operating condition for driver. Taking the"Youth Technological Phosphor Project"of Shanghai City (04QMX1474) as engineering background, a novel suspension height self-centering device is researched and developed in this dissertation. By analyzing the defects of the conventional self-centering devices both for seat and body height adjustment, a novel pure-mechanical scheme with high performance-price ratio is proposed which can realize the self-centering of suspension height but without the need of hydraulic and electrical system hardware and corresponding energy supply.Respectively for vehicle suspension and seat suspension, the structure design, experimental validation, simulation analysis and parameter optimization of the mechanical self-centering devices are sequently performed. The dissertation includes five chapters as follows:In the first chapter (Introduction), the basic functions and performance requirements respectively for seat suspension and vehicle suspension are introduced firstly. Then technical background, including the practical application and characteristics for different conventional height adjustable devices, such as the manually/pneumatically adjustable devices for seat height and the passive/active self-leveling devices for body height are reviewed. Finally, the significance and content of the study in this dissertation are presented.In the second chapter (Novel Design and Experimental Validation), the design scheme of the proposed mechanical self-centering device for suspension height is described in detail. Firstly, taking the driver seat suspension of a particular heavy truck as a preliminary research example, a prototype of mechanical self-centering seat suspension is developed based on the novelly-designed structure. The first-round prototype tests show that this design scheme is feasible except some problems, e.g., relatively high level of noise and friction damping. Hence, an improved design for more significant design subject, i.e., the rear independent suspension of a light bus is proposed. Based on the re-designed mechanical self-centering device for vehicle suspension, a prototype is developed for experimental study. The real road tests proved the effectiveness of the vehicle height self-centering device, so the feasibility of the design scheme is further experimentally validated. Meanwhile, the shortcomings of the prototype in terms of structures and performances are analyzed.In the third chapter (Mathematical Modeling and Simulation Analysis), respectively using multi-body system dynamics modeling method, the mathematical models for both manual-centering and self-centering seat suspensions are built firstly. In order to examine the characteristics of mechanical self-centering seat suspension and make comparison, the performances of both types of seat suspensions in frequency and time domains are analyzed by simulations in SimMechanics software environment with the typical floor-board excitations, i.e., swept and sine wave, etc. Since the body pitch angle must be concerned for body attitude with significant influence on headlight performance, a half-vehicle model respectively with/without self-centering device is established in which both spring and damping nonlinearities have been considered. By using Simulink software, the performances of both configurations with the road excitations of random and pulse are analyzed by simulations, and the main characteristics of the mechanical self-centering vehicle suspension are presented.In the fourth chapter (Multi-object Optimization of Design Parameters), a multi-object parameter design optimization model for the vehicle suspension self-centering device is built by weighted sum approach, and optimal solution is obtained by adopting compound shape approach. Then, the relevant selecting-type parameters for self-centering device components are deduced by using discrete variable optimal method. Finally, the optimal results are verified and analyzed to examine performance potentials of the designed self-centering device in condition of ensuring overall suspension performances.In the fifth chapter (Summary), the research contributions and innovation achievements in this dissertation are summarized and the further work is prospected.