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Research and Simulation on Vehicle¡¯s 4 Wheel Drive System

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Tutor: LvXinMin
School: Northwest University of Science and Technology
Course: Mechanical Design and Theory
Keywords: vehicle,4WD,ADAMS,control system,simulation
CLC: U464
Type: Master's thesis
Year:  2011
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With the development of 4WD technology, some high-performance cars and sports cars began to use 4WD drive system in order to improve their dynamic property and stability. Nowadays, designers have considered 4WD drive system as a part of vehicle control, and they tired to distribute the drive torque to the wheel tires as far as reasonable, according to vehicle driving conditions and road conditions. The force of driving wheel should be changed with the road conditions and drivers¡¯intent so as to improve performances of vehicles. This paper analyzed the characteristics of 4WD and the principles of power distribution, and established a simulation model and control system, under the following steps:First, build a vehicle simulation model in ADAMS, including: chassis model, steering model, the front suspension model, the inclined rear suspension model, tire and road model, and get better results by debugging.Second, establish the principle of power distribution of 4WD; count the distribution ratio via the equation when the car was linear accelerating, climbing and cornering.Third, Two-wheeled vehicle model and four-wheeled vehicle model were established when the car was doing uniform circular motion, analyze the affect of yawing moment on stability factor (K) and turning radius(R). At the same time analyze the singular point in the differential equations about the car was turning; find the stable point when the car was at different speeds and different steering angle.Fourth, analyze the constraints when the car was running; establish constraint equation to get the optimal power distribution. Finally compare the theoretical result with the simulation in ADAMSFifth step is establishing control systems in Simulink, and co-simulation with ADAMS so as to prove the superiority of full-time 4WD by comparing to RWD. Analysis the longitudinal slip rate of each wheel by setting the front and rear load to mimic conditions on the ground. Each wheel longitudinal slip rate change not affect each other, only relevant on vertical load and the driving force when without control system, so the dynamic has not been fully exploited. By adding control system, the longitudinal slip rate of each wheel to maintain the same, show the control system will allocate the power to each wheel reasonable.The results show that the method of analyze the vehicle stability by a mathematical model a better way, simulation model established by Adams will be accurate than by MATLAB, but the control system will be established easily by MATLAB, this paper design a power distribution way by co-simulation.
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