Research On Engine Assembly Accuracy Prediction And Its Application Based On Flexible Hypothesis

Engine is the "heart" of the car,the performance of the car is directly determined the quality and performance of engine.The engine is also a precision thermal machine,consisted of hundreds of precision parts.The precision of the parts and the thermal deformation of the parts directly affect the assembly precision of the engine,and thus affect the engine performance.At present,most engine assembly precision analysis is given priority to with rigid assumptions,it’s difficult to directly consider the flexible deformation of the parts,the traditional Monte Carlo method has the disadvantage of low efficiency when used it to calculate the assembly qualified rate.For the above disadvantages,this paper studies the engine assembly precision analysis technology based on the low-discrepancy sequence and flexible deformation.The main research contents are as follows:(1)This paper introduces the product assembly precision analysis based on the rigidity assumption and the related research based on the flexible hypothesis.The development and research status of computer aided tolerance(CAT)design at home and abroad,point out the shortcomings of existing methods of assembly precision analysis,and the research significance of the thesis is presented.(2)The dimension chain calculation and tolerance optimization technique are introduced.Introduced the basic types and basic calculation method for the dimension chain,the transfer coefficient and contribution rate of tolerance optimization are studied,which is important to tolerance optimization,finally analyzes the GD&T and assembly tolerance effect on assembling accuracy.(3)The dimension chain calculation method based on the flexible hypothesis is studied.The dimension chain calculating model based on flexible hypothesis can be directly considered the flexible deformation of product,it can overcome the deficiency of the traditional dimension chain calculation,and finally the assembly accuracy of crankshaft assembly under the working conditions is calculate as an instance for verified.(4)The Monte Carlo tolerance analysis method based on the low-discrepancy sequence is studied.Based on the low-discrepancy sequence of Monte Carlo method can effectively reduce sampling and improve the computational efficiency of Monte Carlo method based on the low-discrepancy sequence,this paper introduces the methods of non-normal distribution processing,assembly precision analysis model and the calculation method of assembly qualified rate,finally combining the actual case of engine assembly to validate the method.(5)Based on the above research results,design and develop a deviation sequence can consider flexible deformation based on low product assembly precision of the analysis and prediction software system,the system development background,the overall design and function modules in detail.Finally,summarizes the thesis,points out the innovation points of this paper and discuss the next step for the study in the future.