Simulation And Improvement Analysis Of Handling And Stability For A MPV

Vehicle handling and stability, called as "the lifeline of high-speed vehicles", is one of the most important performances of modern vehicle". Study on the handling and stability is often used simulation methods and test methods, as using simulation analysis method takes a short time, and it can be repeated on the various design options for rapid optimization contrast, also, it can achieve harsh status analysis which can not be realized under the test conditions. So it is being used increasingly. ADAMS is one of the software that is widely used in mechanics dynamics analysis.Virtual prototype technique is used in ADAMS, which provides the function of big displacement and non-linear solver, convenient interface and powerful postprocessing system. ADAMS/Car is one of the professional modules, which is mainly used for dynamics simulation and analysis of vehicle (including full vehicle and assemblies).This dissertation was completely supported by the project"G project—Research on Vehicle Dynamics Modeling and Simulation"of a auto manufacturer. In this paper, based on the theory of multi-body system dynamics, created the simulation model in ADAMAS/Car, and did in-depth analysis of the simulation and improvement on suspension kinematics characteristic and full vehicle handling and stability performance. The whole dissertation included six chapters; its main content is as follow:In chapter one, reviewed the status quo and future trend of vehicle dynamics simulation technology, then gave a brief introduction of ADAMS/Car which is used by this paper. Recalled the research of suspension kinematics and compliance, introduced briefly the history. of modeling and evaluation of vehicle handling and stability. Finally, gave this dissertation's content and significance.In chapter two, as a MPV's front and rear suspension are independent suspensions, pointed out more than twenty suspension parameters to evaluate kinematics and compliance characteristic, these parameters reflected wheel alignment, compliance steering, body pitches and roll,wheel returnability, steering efforts and tire attrition separately. Elaborated the influence of these parameters on vehicle performance; gave their reasonable change tendencies and scopes. This acts a aggregate role. Because there are many mutual influences or even some contradictory relationships between each other, the choice of evaluation must be considered. Then according to the vehicle's linear model of two freedom, launched into a detailed explanation about the basic theoretical analysis of handling and stability, listed the common test evaluation method.Chapter three is divided into two parts, discussed the performance of a MPV's front and rear suspension in the project respectively. At first, modeled the front torsion bar independent suspension of double-wishbone type spring with rear longitudinal rod in template builder interface of ADAMS/Car. The lower control arm was simplified as a arm. joined to the body by two bushings of great stiffness. Beam is used when modeled torsion bar to ensure the accuracy of simulation results in the greatest extent. Then performed a parallel wheel travel analysis. The toe angle and wheel rate curve descended rapidly along with the wheel travel up, the anti-dive is bad. In the guide of modify as few as better of the parts, made the lower control arm's front point connected to the body 10mm down. This slowed the curve's descend trend. Then modeled the rear coil spring independent suspension of single oblique arm type. As the MPV is a FR one, modified the corresponding drive shaft assembly. After a parallel wheel travel analysis, got change curves of some parameters, such as wheel alignment and suspension stiffness, when wheels bumped and rebounded in this paper. Rear suspension performance is good, no need to improve. Here, it is very important to fully understand the various connections between the communicator when modeled the tsemplates.This method can rapidly and accurately assess the performance of a suspension, parameter optimization, as well as structural improvements, a broad application prospect.In chapter four, according to various parts's CAD solid model parameters and structure size, modeled templates such as steering system, front tire, rear tire, body and powertrain system, and calculated their dimensions of freedom respectively, based on analysis of front and rear suspension. After determining the need for spring components, damping components, rubber bushings, and other parameters, modeled every subsystem according to correctly handling the connections between various components and constraint relationships. Then modeled the full vehicle dynamics simulation mode after debugging.In chapter five, defined the Driver Control Files based on"GB/T6323.1-1994 ~ GB/T6323.6-1994 Contorllability and stability test procedure for automobiles". Steady static circular test procedure, Steering wheel angle step input and Returability test were run for the full vehicle dynamics model, The simulation results were evaluated for model based on"GB/T13047-1999 Criterion thresholds and evaluation of controllability and stability for automobiles", the scores were 89.35, 86.83, 99.50. The above analysis showd that degree of understeer was more, so got some corresponding improvement measures.Through the analysis of the two-track model of four wheels vehicle, select a number of factors that affects handling and stability. Surrounding each of the main changes in the test, made improvement analysis of Steady static circular test. Evaluated the degree of understeer according to overload with inadequate to the situation. The result was better. These factors were front suspension's torsion bar spring stiffness, front wheel alignment parameters, rear suspension's coil spring stiffness, tierod position and anti-roll bar's torsional stiffness. The scores were 88.16, 85.62, 88.58, 84.68, 87.1. According to analysis of these improvement measures influencing the wheel rate,①although decreasing torsion bar spring's stiffness increased 11.84 points, lowered the high-speed returability, impacted the wheel rate greater, decreasd stiffness 26.56%. So the programme was undesirable.②Changing alignment parameters diminished magnitudes of toe angle and wheel rate, and it also decreased the stability time of yaw velocity. It was beneficial to improvement of suspension performance and vehicle handling and stability. This made the degree of understeer—U increasing 9.3 points—detailed in analysis of 3.1 and 5.5.2.③Increasing coil spring's stiffness and decreasing anti-roll bar's torsional stiffness made U increasing 8.1 and 6.28 respectively. As to impact of wheel rate, the percentage was 2.58% and 3.57%.④Changing tierod position made U increasing 7.23 points, but this didn't affected wheel rate and made the changing rate of toe angle decreasing 13.185%. To sum up, chose the last four improvement programmes. In this dissertation, the analysis of simulation and improvement could provide a basis for the subject.Chapter six was the summarization of this dissertation. Depicted the research work, related conclusion and meaning of this dissertation, and listed some of the future research work.This dissertation successfully applied the dynamics simulation in the development of suspension and full vehicle, and made improvement analysis for a MPV. But there still needed further settlement to get simulation match practice perfectly.