| Heavy duty vehicle is an important tendency of truck development, tractor-semitrailer are playing an important role in long way transportation. Taking heavy duty truck as the target, this dissertation presents contents and methods of a study on performance control at design stage. As performance control relates to many aspects, this dissertation only studies part of performances of steering system, pneumatic braking system and tractor-semitrailer combination. The following are the focus: Modeling of subsystems, analysis and comparison of simulation results of plans; Analysis of test results of subsystem; Modeling of subsystem basing on tests, application of the model; Model Creation of tractor-semitrailer combination, model validation and simulation; Vehicle performance analysis aiming on structure characteristics, subsystem selection. In Chapter One, requirements of performance control at heavy truck design stage are figured out, and the research methods and contents are given. In Chapter Two, truck steering system are studied. Steering system performance affects much the whole vehicle performance. In steering system design, not only the steering function but the harmonization with other systems should be considered. Firstly, the kinematics model of truck steering system is developed, evaluation criteria is given, analysis and comparison of two plan are carried out. Secondly, stand still steering performance is studied, which relates much to tire, system friction, power steering box, etc. Calculation method is work out, Calculation and analysis is applied for two steering devices matching two power steering box with different efficiency. The results show that more attention should be paid to utilization coefficient of steering box output angle, symmetry of steering angle transfer and efficiency of steering box. After that, a kinematics model including steering system and leaf spring suspension is work out. And the model is applied to calculation and analysis of two matching plan under different working conditions. The Third Chapter is about pneumatic braking system. The braking system of heavy duty truck is relatively complex, many factors need to be considered at system design stage. Also the characteristic of pneumatic braking system is difficult to describe theoretically. At first step, a series of test are done to get the characteristic of actuator force, capacity, draw back force, and draw back resistance, free travel of auto slack adjuster, actuation deformation of brake assembly, etc. After that, working characteristic of pneumatic system is studied, and an experimental model of pneumatic braking system is created. With the model, the energy storage device capacity is verified according to the regulation, harmony character of design value of rated braking pressure and cut in pressure , Influence of slack to brake force are analyzed. Energy storage device capacity of derived vehicle is also calculated. At the end of the chapter, the affect of push out pressure on brake torque and brake torque response is studied and analyzed. Chapter Four is emphasized on dynamics model of tractor-semitrailer combination. The reasoning process is rather complex, only the hypothesis, coordinates, attitude of the combination are described in the dissertation, and final math formulas are given. The model is validated and problems including jackknifing, swing and roll over are simulated and analyzed. Using the tractor-semitrailer combination model created in Chapter Four and system model and conclusions drawn in Chapter two and Chapter Three, Chapter Five is mainly on whole vehicle performance analysis and optimization. the following work are included: a) Influence of dual tire and double drive axles on 6x4 tractor. Study result shows that while turning, the dual tire have different longitudinal slip ratio, but it has little influence on vehicle performance and can be simplified as overlapped at the center of dual tire. But the double rear axles affects more on vehicle performance because of the distance between two axles. Comparing with a 4x2 vehicle, a vehicle with double rear axles has bigger turning radius, bigger under steer tendency and is less sensitive to steering input. This should be taken into account in steering system design. b) Study on 6x2 tractor with a lift axle shows the side slip angle of tires on the lift axle are notable biger then that on the drive axle, the distance between two axles and the total side slip stiffness of lift axle tire is less then that of the drive axle are main reasons. And bigger side slip angle is the main reason why tires on the lift axle more likely wear out. Shorten the distance between two rear axles is a solution. c) Torsion flexibility of chassis makes it impossible to transfer big roll torque between front axle and rear axles. Simulation result indicates the way adjusting steering... |
PDF Full Text Request