Dynamics And Finite Element Analysis On The Back-Mounted Working Device Of Bulldozer

Bulldozer is a important kind of engineering vehicle, which widely used in the field of city construction, highway and railway construction, water conservancy and hydropower construction, open pit mining, national defense and so forth. It can remove soil, excavate channel, fill, clean, etc. A crawler dozer which has very good cross-country performance and powerful traction can be also used to push a scraper, assist scrapping, and with a ripper, it can do ground-breaking operation. According to some data related, 25% ~30% of works in earth and rock engineering are done by bulldozers. So it is our first choice to use dozers in many projects.The history of crawler dozers in China begins at 1958, when the backward technology and very limited quantities could not meet the needs of domestic construction. We had to bring in lots of bulldozers from abroad. Nowadays, we can produce many kinds and series of dozers by ourselves but there are still some quality gaps compared with foreign products.The ripper is a back-mounted working device of bulldozer or other tractor, which completed the function of bulldozer with the blade. With the development of hydraulics, the structure, control and working capability of rippers have advanced a lot. They are widely used in engineering construction and mining to scrap the rocks and hard soil, replaced the original way that blow with explosive, which not only advanced the safety and efficiency, but also lowered the cost of production.There are many differences in the methods of analysis on the mechanical of the rippers between home and abroad. Dynamics and finite analysis with advanced simulating software are using extensively abroad, which based on the current working data on dozers. On the other hand, we still use the original analysis method domestic. Although we can get the accurate result through the original method and empirical formulas, it works only in some particular cases. It's not practical and applicable extensively. This thesis which based on the original analysis method, used modern mathematical methods, generalized special circumstances, and then used some simulation software according to virtual prototyping technology. Not only in this way it turned out the results to be practical and accurate, but also the method a modem designed methodology.Based on original analysis method, rippers can be analyzed in three circumstances: Condition One, the bulldozer is static while the ripper tries to break into the ground. With the continual forces from the hydraulic cylinders, the bulldozer has tipping tendency. Condition Two, the bulldozer does uniform motion while the ripper is at the deepest position. Condition Three, the bulldozer is static while the ripper tries to promote itself against the obstacles at the deepest position, with the continual forces from the hydraulic cylinders, the bulldozer has tipping tendency. Based on experience, in Condition Three, the maximum forces are much less than that in the other two circumstances. Condition Three is used only when we design parameters of the hydraulic cylinders. So it will be out of the discussion in this paper. The maximum forces appear in the first two conditions.Established mathematical model based on empirical formulas, calculated with MATLAB, then we found that in Condition One, the maximum forces on the tilting hydraulic cylinders are much bigger than their limits when the tilting hydraulic cylinder located at their shortest length and the lifting hydraulic cylinder the longest, that is when the ripper at its deepest position. So, tilting hydraulic cylinders cannot work normally nearby this position. In Condition two, the maximum forces on hydraulic cylinders are also much bigger than their limits when the tilting hydraulic cylinder located at their longest length and the lifting hydraulic cylinder the shortest, that is when the ripper at its highest position. Therefore, we drew a clue that not in any condition can the ripper works normally. So the ripper must have a working range. It won't be safe when it is out of range at work. It is improvable for the ripper. Strokes of hydraulic cylinders, length of the shaft and distances between hinge points can be redesigned so that the ripper can work in more conditions and at more positions.Virtual prototyping technology is mainly used in this article as a vital method, which established a model on the computer, with CAD modeling technology, computer supported cooperative work (CSCW), user interface design, knowledge-based reasoning technology, design process management and document technology and integration of virtual reality technology, to form concurrent engineering methods based on computer and desktop of the distributed environment to support the design. Its trueness can be the same as the real one to some extent. So we can replace the real model with the virtual prototype to test and evaluate the characteristics and parameters of every candidate design.This thesis is based on former empirical formulas, established mathematical models in limit conditions and then generalized it to all conditions, so that makes it clear that what the state would be like in all conditions and at all positions. However, this method contains five-dimensional nonlinear equations which can't be calculated by normal analytical method. So MATLAB has been used. The results remain to be confirmed owing to a large use of iterative methods. Another method, virtual prototype technology,used in chapter 4, used three-dimensional software for dynamic simulation on the ripper, in some dangerous conditions, compared with the former results, confirmed the both two methods were correct and accurate and the mathematical modeling is proper because of their results are almost the same (relative errors are within 5%).The sizes and directions of forces are known macroscopically in the previous chapters, finite element analysis of static is used in chapter 5. Both the strength and stiffness can meet the requirements based on the result of analysis on the shaft, the arm and hydraulic cylinders. Plastic deformation or fracture will not occur due to the deficiency of strength and stiffness. There is no shape defect caused by welding because of the arm and the hydraulic cylinders are idealized in the model, so the stress is much less than their allowable one.