The Design And Research Of Double Front Axles Steering System In Heavy Duty Commercial Vehicle

The appearance and the research of a double steering axles vehicle have something to do with the more and more load of the vehicle. After comparing we know that the price of four-axle vehicle is 10% higher than the price of three axle vehicle,but its load can be 20%～30% more than that allowed in regulation of the nation. With the widely use of the multi-axle vehicle, realizing multi-axle steering is the most important question for discussing in chassis design. The mechanism of steering system also become more complex. With the increasing number of axle, its performance must be better. If we want a better steering performance of multi axles steering vehicle, we need design the linkage parameter of steering system.properly, make the turning angle of wheels have right relations, avoid much transverse slide of the tire and minimize the tire wear. These aquirements need us to practise and explore. The designers are more and more interested in the research of multi axle steering vehicle. At one time many college and factories announce many theories on it. Most of them foucs on the optimization theory. In the early time most of the research work simplify the steering geometry in one plane, the computing can be very easy by this way, but the precision will be effected excessively,It result in much deviation between the computing result and the practical result . In this paper,a three-dimension mathmatic model was established, the cordinations of the main nodes were worked out by the space transfer matrixes. And then we can describe the turn angle of every tire.This paper is based upon the CA1303P7K2L11T4 designed by R&D center. It divided into six chapters. In the first chapter,two type multi-axles steering system were introduced first,then diversiform layouts of steering link were compared ,at last the final layout was set down.The second chapter is mainly about the research of the multi-steering axles kinematics, the basic requirements of steering system design were put forward, the main parts of steerng system were introduced. In the second chapter, the Ackerman relationship was discussed. In this chapter we establish the three-dimensional mathmatic model, use triangle fuction and transform matrix to work out the coordinates of steering mechanism nodes,and the turning ange of tyre。The third chapter is mainly about the research of optimal design of steering links. In this chapter the ideal of optimizing steering mechanism is made certain, the double axles steering system was regarded as link system.but it is not easy to think about all factors relate to the whole steering system and make the link right and meet the requirements of steering system. According to the theory of steering, the ideal condition is that all wheels axle must intersect at one point when the vehicle is turning. It can make all wheels roll without side slide. But realizing it is impossible for the wheel in every position .we can only approach it by optimise design. Our aim is minimizing the deviation between the real angle and the computing angle by mathmatic model and making the vehicle steering properly in the whole wheel range.In the process of optimizing, the selection of design parameters affects the quality and the result of design directly. If all the parameters which relate to the result were set to be the design parameters, it would be very complex to work it out, and it is also not necessary. So we need to compare all the parameters affecting the result, select those parameters which have something to do with the design object as the design parameters and regard the others as constant. If the design parameters is too few, the optimizing result can not be worked out. So we should decide the final parameters according to these two factors. As to the double front axles steering system, the parameters which affect the angle relations of the wheel should be selected as the main design parameters. After analysing we confirmed seven design parameters.We use a program compiled by MATLAB software to optimize the steering links and compare the result with which were worked out by PRO/E and ADAMS simulation. The final conclusion is that three ways all meet our demand, but the method using PRO/E software adapt to our design works better. In this chapter, we also analyse tyre abrasion and improve it. The synchro angle is the important factor which have something to do with tyre abrasion after experiment.The contents in fourth chapter is mainly refer to the kinetics analyse of the dual-front-axle steering system. In the dual-front axle steering system, steering links are much more. The diameters of these parts should not be too big, because too big diameter will cause many difficulties in the system layout. But too small diameters will result in lower rigidity of steering link. It will affect the synchronization of the two front axles and is easy to have the problem of tyre abrasion. So we should process a kinetics analyse on the steering links, work out the loads in the links. These can provide the load conditions for the finite element analyse and advise us to layout the links and design the link shape properly. In this chapter we use PRO/E software to simulate the steering system, solve the load in links while the vehicle steering in park and process the finite element analyse to the new design. All these computing reduce the risk effectively.The contents of the fifth chapter is mainly about the experiments. Any simulation by computer can not replace the experiments, so we need measure the angle and the load of links based on the computing results. After experiments, the computing results and the experiments result are very near. It proved that the theory of computing is right.The sixth chapter is the summary of the whole thesis and forecast the foreground of this specialty field.