| As an important part of engine connecting rod group system, connecting rod bolt is mainly used for connecting rod big bonnet, connecting rod bearings and rod body, as well as suffering all occurring forces of connecting rod system. Therefore, connecting rod bolt is suffering from stretching and bending alternating load and lateral vibration loads. Since connecting rod bolt works in a harsh environment, fracture failure may happen. If there’s connecting rod bolt failure, the engine would be destroyed malignantly, which may lead to engine scraping, as well as harmful for the safety of tester and vehicle user. Therefore, to guarantee the reliability of the connecting rod bolt will keep engine’s stability and reliability.In this paper, connecting rod bolt tightening and mechanical conditions of service are considered. By analyzing stress state of connecting rod system and connecting rod bearing, a reliability design rule based on remaining preload coefficient and ultimate pressure for the connecting rod bolt is established. Meanwhile, criterion of reliability design of connecting rod bolt is built basing on statistical analysis and verification test evaluation. Through finite element calculation, fatigue test and durability test, rationality of design criterion and evaluation standard is determined.In the paper, common tightening methods of connecting rod bolts are analyzed. Through theoretical analysis and comparison tests, torque angle plastic method is confirmed as the optimal tightening method for connecting rod bolts. The paper analyzes the calculation method of springback extension rate of connecting rod bolt and springback of connecting rod end cap using theoretical mechanics, as well as summarizes the calculation formula. Calculation criterion of the torque angle plastic method is established by analyzing mechanical model of connecting rod bolt. Through tightening process comparison test, the rationality of the calculation of the connecting rod bolt torque angle plastic method is determined.In this paper, the condition of the test equipment for connecting rod bolts is introduced. According to the advantages and disadvantages of each equipment, the optimal matching equipment is chosen. Through test verification, the paper assures the consistency of the tightening process when the connecting rod is processed with the connecting rod. Through connecting rod bolt tightening service condition and the existing equipment condition, a set of test method of connecting rod bolt tightening technology is established.The paper takes design and verification of connecting rod bolt as the main line, which fully verifies the rationality of the established criteria and methods.1) Reversely develops a connecting rod bolt of certain type of engine by using criterion built by this paper, builds torque angle plastic guidelines for the calculation of tightening process by running text, as well as establishing the identified the connecting rod bolts calculation tightening process.2) Use the test criterion of tightening procedure which established in this paper to determine the testing technology of the connecting rod bolt. Through tightening process comparison test of connecting rod bolt, the tightening procedure calculation is the same as the test tightening procedure of connecting rod bolt, which proves the rationality of the connecting rod bolt tightening process calculation criterion.3) By strain testing, big end hole of connecting rod deforms little, roundness of connecting rod’s big end hole meets the design requirements, which proves rationality of the connecting rod bolt tightening procedure.4) Through finite element calculation, make sure static strength and fatigue strength of connecting rod bolt and connecting rod, bearing pressure, tangential force, and divided surface slip of rod cap all meet requirement, which proves the reliability design of connecting rod bolts.5) Through fatigue test of connecting rod, connecting rod bolt does not loose, there’s no invalidation surrounding connecting rod bolt and connecting rod fatigue safety coefficient meets requirement, which proves design and tighten the connecting rod bolts are reliable.6) Through engine durability test to assure the connecting rod bolts do not loose off, connecting rod does not fail, rod bearing and the connecting rod big end cover are normal, which means engine durability test passes the examination, as well as comprehensively verifies the reliability of the connecting rod bolt design and tightening. |
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