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Research on All-wheel Steering Control Strategy for6×6Unmanned Vehicle

Author: TanHui
Tutor: CuiShengMin
School: Harbin Institute of Technology
Course: Vehicle Engineering
Keywords: 6×6unmanned vehicle all-wheel steering optimal control fuzzycontrol dynamic stability
CLC: U463.4
Type: Master's thesis
Year: 2013
Downloads: 3
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Abstract

As the national economy constantly develops, the national defense constructionand space exploration grow rapidly, and multi-axis unmanned vehicle is widely usedin these areas for its characteristics that it is suitable for complex risk environment.These areas’ special working environment puts forward higher requirements for themulti-axis unmanned vehicle’s performance and researching on highly adaptable andhigh dynamic stability multi-axis unmanned vehicle is of great importance. Steeringsystem plays a vital role in the dynamic stability of the vehicle, so multi-wheelsteering system which can improve vehicle steering performance is an importantresearch direction of the multi-axis unmanned vehicle. At present, research literatureon the multi-wheel steering technology is little at home and abroad. Study onall-wheel steering control strategies is less, and most papers’ all-wheel steeringvehicle models are simplified models which ignore a lot of factors. In this paper,modeling and all-wheel steering control strategies on6×6all-wheel steeringunmanned vehicle are researched further.The accuracy of the mathematical model has a great influence on multi-axisvehicle’s all-wheel steering control strategy.6×6unmanned vehicle’s specialworking environment determines that the suspension’s influence on the steeringsystem cannot be ignored and tire cornering properties present nonlinear, soclassical linear2-DOF (2-degree of freedom) model cannot accurately describe it’sactual dynamics. In order to solve the problem of solving6×6unmanned vehicle’stire vertical loads, the tire vertical load’s solving method based on displacement isapplied. Considering the body roll DOF and using the tire’s magic formula, anonlinear3-DOF model of six-wheel all-wheel steering vehicle is built in this paper.At last, simulation analysis is carried on.Optima l control is able to balance the various evaluations. When the selectedevaluations are too many, its advantages can be better used. In this paper, an idealreference model of6×6unmanned vehicle is built by analyzing the vehic le’sstability. After this, an all-wheel steering zero sideslip angle proportion feedforwardand optimal feedback control strategy is designed to control the rear two axes’steering angles to realize all-wheel steering. In order to reflect the superiority of thisstrategy, the front wheel steering, zero sideslip angle proportional control all-wheelsteering are simulated together with the optima l control strategy. Simulation resultsshow that this strategy can coordinate the indicators to reach a comprehensiveoptimal effect, which improves the vehicle’s dynamic stability.Fuzzy control has its unique advantages in dealing with nonlinear problems. Considering the study object is non-linear mathematical model, all-wheel steeringproportion feedforward and slip angle fuzzy feedback control strategy targeting atkeeping centroid slip angle to zero is designed, and all-wheel steering proportionfeedforward and yaw rate fuzzy feedback control strategy targeting at making yawrate track ideal yaw rate is also designed. By analyzing the simulation results, thesetwo strategies can only control single variable. In order to improve the shortcomings,all-wheel steering proportion feedforward and sideslip angle and yaw rate jointfuzzy feedback control strategy is designed. Simulation results show that theimproved control strategy can control multiple variables at the same time and makethem close to the ideal value, which improves the vehicle’s dynamic stability.Finally, in order to reflect the superiority of the all-wheel steering optimal andfuzzy control strategies, the6×6unmanned vehicle’s front wheel steering, all-wheelsteering proportional control strategy, all-wheel steering proportion feedforward andoptimal feedback control strategy and proportion feedforward and sideslip angle andyaw rate joint fuzzy feedback control strategy are written in MATLAB/Simulink, thesimulation results show that the two all-wheel steering control strategies canimprove the dynamic response characteristics of the vehicle.

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