| Since the birth of the internal combustion engine,the crank and connecting rod mechanism is widely used in the automobile engine to realize the work cycle and complete the energy conversion.The propulsive force produced by the combustion of the combustible mixture is transmitted from the piston to the connecting rod,and finally to the crankshaft.During this process,there is a lot of mechanical loss,one of the most important reasons is that the swing angle of the connecting rod is so large that the piston exerts a large lateral pressure on the cylinder,reducing the conversion efficiency from internal energy to mechanical energy.The large lateral pressure also increases the friction loss between piston ring and cylinder sleeve,which leads to many problems,such as shortening the life of the engine and the vibration of the engine.In this thesis,a new power transmission mechanism of the engine was proposed,which was based on the research of the working characteristics of the crank rocker mechanism.It was introduced to the engine power transmission mechanism,replacing the traditional crank connecting rod mechanism.The new power transmission mechanism based on the crank rocker mechanism can meet the requirements of the engine working cycle and it can be stable and reliable to complete four working strokes of the engine,with a small connecting rod of the swing angle,and small side pressure on the cylinder,which can reduce the friction loss between the piston ring and engine cylinder sleeve,prolonging engine life;The use of straight axis instead of the crankshaft,can save the processing cost.The main research contents of this thesis are as follows:(1)The motion of the traditional engine crank and connecting rod mechanism was analyzed.The defects of the power transmission were explained from the aspect of the influence factor of the transmission efficiency,and shortcomings are explained from the aspect of the coordination between the pressure angle and stroke crank.(2)Basic conception of new power output mechanism of engine was put forward.The characteristics of quick-return and dead point were analyzed.The feasibility of the application of crank rod mechanism used in the engine power output mechanism was fully understood.The working principle of a new type of mechanism was discussed.(3)The dimension optimization of the new structure was carried out with MATLAB,to achieve the highest efficiency of the new mechanism,the weakest quick-return characteristic and the smallest occupancy space.The motion law of the new mechanism after the optimization was calculated and analyzed and the advantages of the new type of mechanism in the connecting rod were demonstrated.(4)The solid model of the new type power output mechanism and the traditional crank connecting rod mechanism was established with the three-dimensional design software SolidWorks.The kinematics simulation analysis was carried out after the model was imported into ADAMS software.The correctness of the model and the accuracy of the simulation system were verified by the comparison between the results and the theoretical calculation.The dynamic simulation analysis and comparison of the new mechanism and the traditional crank connecting rod mechanism were carried out to verify the advantages of the new mechanism in reducing the pressure of the piston on the cylinder side.(5)The static analysis of the main parts of the new mechanism were analyzed with ANSYS finite element analysis software,and lay the foundation for the structural optimization of the parts.(6)Design of experimental apparatus.The design scheme of the experiment were described,and the selection method of the screw pair and the stepping motor was discussed,which lays the foundation for the processing of the experimental apparatus.(7)The machining of the experimental apparatus was made,and the working condition of the new type of mechanism and the feasibility of the new type of mechanism used in the engine were also verified by experiments. |
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