Design Of Engine Timing Silent Chain System For Hybrid Passenger Vehicle

This paper is completed under the joint support of the National Natural Science Foundation of China（NSFC）project "Variation Mechanism of Silent Chain and its Key Design Technology（51775222）" and the Key Research Project of Jilin Provincial Science and Technology Development Program "Research on Key Technology of Engine Timing Chain System for Hybrid Passenger Car（20200401136GX）".Hybrid passenger cars are becoming more and more dominant in the market due to their excellent fuel economy and driving performance close to that of pure electric vehicle.Conventional full-service engines cannot take advantage of the high efficiency in the new operating conditions of hybrid system.To this end,the major manufacturers have developed a variety of high thermal efficiency engines for hybrid conditions through improving the design,reducing friction losses and other new technologies.However,the timing silent chain system,which is an important part of the engine,still lacks improving work for hybrid conditions,and there is still room for improvement in reducing mechanical losses and improving thermal efficiency and NVH performance.Based on the technical characteristics and operating conditions of a hybrid passenger car engine,this paper studies the timing silent chain system and oil pump silent chain system.The paper firstly introduces the progress of domestic and international research on hybrid passenger car engine and silent chain,and explains the significance and background of the research work.After that,the basic knowledge of hybrid power system is briefly introduced,and the design ideas of timing silent chain system and oil pump silent chain system of hybrid passenger car engine are proposed based on the characteristics of operating conditions and technical improvement of hybrid passenger car engine.According to the design requirements of the timing silent chain system and oil pump silent system of a hybrid passenger car engine proposed by an OEM,this paper designed the parameters of the chain system according to the silent chain meshing principle and the design method proposed in this paper.In addition,the geometric models of the timing silent chain system and oil pump silent chain system are established.The results show that by redesigning the chain plate tooth profile and adjusting the chain structure with the working conditions of the hybrid passenger car engine,the chain system finally reduces the weight by about 25% and meets the strength requirements,and the light weight helps to reduce the mechanical loss and improve the response speed.In addition,under hybrid conditions,the engine timing silent chain system engagement frequency changes from200HZ～2000Hz to 400Hz～1500Hz,which avoids the lower the lower order inherent frequency of the chain system,and the reduction of the part quality makes its inherent frequency avoid the higher engagement frequency,and the engine NVH performance is more guaranteed.The dynamics models of the timing silent chain system and the oil pump silent chain system are established to study their dynamic performance under the load setting closer to the actual operating conditions.The trajectory of the chain plate,the tension between the chain links,the tensioning force of the tensioner and the variation law of the instantaneous transmission ratio in the system are analyzed by simulation.The results show that the silent chain system of small pitch chain plate with internal and external compound meshing mechanism has good transmission characteristics.The polygonal effect is not significant,the deviation of running trajectory is extremely small,the transmission ratio error is basically kept within 0.5%,the maximum does not exceed 1%.The maximum tension safety factor of tight edge meets the requirement of tensile strength,the operation is smooth and reliable,and the dynamic performance is excellent under the hybrid working condition.Based on the above work,the stress change law of chain plate and pin in the working process of chain drive system is analyzed by using rigid-flexible coupling technique,and the distribution of stresses in time and space of chain plate and pin is analyzed with the focus on the meshing process.The results show that the internal and external composite meshing mechanism can well reflect its superiority.The weak point of fatigue damage of the chain plate occurs at the crotch position of the chain plate and the Y-direction position of the pin hole,and the weak point of fatigue damage of the pin occurs near the shear surface,but the extreme values of the stresses meet the material strength requirements.The number of stress cycles of the chain plate and the pin is predicted by using the life analysis module.The results show that the fatigue life can cover the whole life cycle of the engine,and the pin is the weak link of the chain compared with the chain plate.The results show that the fatigue life can cover the whole life cycle of the engine,and the pin is the weak link of the chain compared with the chain plate.In summary,the design method of the silent chain system proposed in this paper is practical and feasible,and the timing silent chain system and oil pump silent chain system designed accordingly have good transmission characteristics and meet the design strength requirements.the fatigue life can cover the full life cycle of the engine,and the NVH performance is further improved.