Structural Design Strength Analysis And Experiment Research Of A Commercial Vehicle Frame

Frame is a main load bearing component of the truck. Based on longitudinal beam characters, the frame can be divided into the ladder type frame, X-type frame, and backbone type frame. The load bearing mechanism of the frame is extremely sophisticated. At standstill, supported by the suspension system, the frame bears the load and gravity of all the components of the truck; and when the truck is running, due to the action of load, and mass and working load (e.g. driving power, braking force and steering force) of all the components of the truck, the frame will have to endure randomly variable dynamic load from different directions and to different degrees. The bend, eccentric twisting and overall twisting may occur to the frame under action of various loads.In the previous design practice of Commercial Vehicle frame, the traditional experience is frequently adopted. The sectional dimensions of longitudinal beam and structural form of cross beam are monotonous, the distribution of cross beam is too simple, and the gross weight of the frame is heavier, and therefore, stress concentration may easily occur on local area.For modern cars, requirements for riding comfort, lightweight and high speed design, structural strength of the frame, bend and torsional vibration generated at external excitation, and gross weight based on cost effect and oil consumption have become increasingly higher, and been subdivided. With rapid development of the automobile industry, requirements for car performance are getting higher and higher so that the traditional design and calculation method can no longer meet the requirements for design of modern car. Emergence of the electronic computer and rapid development of the finite element method have brought a new revolution for calculation and analysis of the structural performance of the frame. The finite element method is used to conduct the performance analysis for the frame structure, and the structural optimization of the frame is taken into consideration in the design, which is of great significance for improving all the performances of the whole car, reducing the design and manufacturing cost, and increasing the market competitive power.The author of this thesis has designed a complete process workflow in combination with these requirements: Starting from the market and input to the whole vehicle, it determines the overall sizes, material and other parameters of the frame, then, it determines the structural dimensions of the longitudinal beam and cross beam, respectively. Upon completion of strength and forming process analysis, and subdivision of the frame assy. 3D drawings, it makes the finite element checking and analysis for the frame assy. Upon completion of the trial assembly of the frame assy., it makes the modal test, and analyzes and solves the issues found during the test.This thesis has the following achievements:New material and manufacturing technology are adopted. The new high strength steel plate is adopted, which can improve the yield strength utmost limit of the material itself, and greatly improves the load bearing capacity without increasing the dimensions.New design and calculation method and strict design procedure are adopted. The finite element method for calculation of the frame is popularized in all aspects. Based on the finite element calculation for static bending of the frame, before completion of the product engineering drawings, the finite element calculation for the whole frame is conducted at first. The previous practice, i.e. completion of product engineering drawing before the finite element checking calculation, is changed. The deepgoing customer investigation is conducted to know the actual application conditions of Chinese users so as to get rid of blind copying, and presents its own product features. Standard holes are adopted on the web of the longitudinal beam of the frame, which can cut down the types of the cross beam of the frame, simplify the stamping process of the longitudinal beam and assure the universal use of other assemblies and parts on trucks within the same series or cross-series. Further, it can reduce the work quantity for layout on the modified truck and facilitate refitting. Therefore, the refitting factory does not need to make additional drilling when refitting, which can protect the paint finish. It can also optimize the piping and wiring, improve the appearance, and facilitate refitting operation.When the developed width of the longitudinal beam is set, and when the ratio between the height of the web plate and the developed width of the longitudinal beam is equal to 0.75, its resistance to bend is the utmost.Both upper and lower wing faces of the longitudinal beam should be equal. If there are the upper and lower reinforcement plates, then, the sizes of the upper and lower reinforcement plates should be same.To improve the resistance to bend of the channel section beam, adhesion of reinforcement plate to the wing face will present better effect than apply it on the web plate. To raise the height of the wing face will produce obvious action to the resistance to bend of the channel section beam.Drilling on the web plate, especially drilling on area near the neutral shaft, will produce much lesser influence on the bend resisting area factors than drilling on the wing face, and in consideration of the influence of holes on the wing face to the stress concentration, the important conclusion can be made that in principle, no drilling shall be made on the wing face of the channel longitudinal beam of the frame.For cross beam of complicated forms, the forming process can be analyzed at first so that preliminary judgment can be made to process performance of the cross beam without waiting for completion of the trial manufacturing dies. In such a way, the part forms can be regulated in time so that not only the development time can be saved, but also the waste of tooling dies can be avoided.Sometimes, the failure cause of parts cannot be concluded via experience. Therefore, the finite element analysis and other methods shall be used to assist the judgment. Most of the strength failure need reinforcement means, however, the increased rigidity is not necessarily a good solution. Instead, the force bearing conditions and deformation tendency should be analyzed according to the position and surrounding environment of the part (structural rigidity and force bearing status) so as to reasonably determine the structural rigidity and strength of the parts designed.