混合动力车辆加速工况发动机介入抖动的分析与优化

Analysis and optimization of engine shaking in hybrid electric vehicles under drive conditions

混合动力车辆在电池电量较低、城市路况拥堵的情况下行驶时,为保持电池电量,发动机会频繁地启动发电,从而引起整车抖动问题。该文建立了混动总成发动机介入抖动的物理模型,采用仿真和实验相结合的方法,研究了混动车加速过程中发动机介入瞬间的抖动产生及路径传递机理。结果表明:发动机介入瞬间的抖动出现在发动机点火之前的集成启动发电一体化发电机(integrated starter generator, ISG)倒拖发动机阶段,其抖动水平由第一循环缸压峰值大小决定;混动总成瞬时刚体模态和传动系扭转模态耦合作用提高了发动机介入抖动水平,并将抖动通过动力总成悬置传递至车身。基于该结论,提出了传动系和动力总成模态解耦原则与优化悬置限位结构2项优化措施,并结合整车测试验证了所提措施有效。

[Objective] The engines of plug-in hybrid electric vehicles work much more frequently under low state-of-charge conditions compared to those of fuel vehicles,resulting in unignorable shaking when the engines are started.Most previous studies have focused on the mechanisms of engine shaking under engine start conditions and not under drive conditions.However,because of the drive motor torque effect,the mechanisms of the engine shaking between the engine start and drive conditions are considerably different.Therefore,studying the mechanisms of engine shaking in hybrid electric vehicles under drive conditions is considerably important.[Methods]In this paper,a physical model,which includes the torsional vibration physical and powertrain(PWT)rigid physical models,is developed to describe the phenomenon of engine shaking in hybrid vehicles.Subsequently,an experimental scheme for the engine shaking is designed.In addition,the physical model is validated through experiments.Finally,the excitation source and transfer path mechanisms of the engine shaking in hybrid electric vehicles under drive conditions are studied by coupling simulations and experiments.[Results] Results showed that:(1)Engine shaking occurred before the internal combustion engine(ICE)sparking,which greatly differed from that in the case of fuel vehicles.(2)Engine shaking was strongly dependent on the first-cycle cylinder pressure during the integrated starter generator pulling ICE to increase engine speed for sparking.In addition,the first cycle cylinder was dependent on the crankshaft position,causing the randomness of engine shaking.(3)The other root cause of this phenomenon was the coupling effect between the PWT rigid model and the torsional model of the driveline.(4)The PWT transient rigid model was strongly influenced by the torque of the drive motor under different drive conditions,affecting the coupling between the PWT rigid model and the torsional models of the driveline.(5)The transfer path of engine shaking was from the engine mounts to the vehicle body.Based on the results,two optimization solutions were proposed:The first solution was decoupling the PWT rigid model from the driveline torsional model by lowering the frequency of the torsional vibration damper model.Another solution was reducing the nonlinear dynamics stiffness of PWT mounts by optimizing the metal frame of PWT mounts,enhancing the vibration isolation from PWT to the vehicle body.[Conclusions]The complex coupling mechanisms from the excitation source to transfer paths for engine shaking under drive conditions are found by integrating simulations and experiments.The two optimization solutions are applied to a hybrid electric vehicle,which can considerably reduce engine shaking under drive conditions.These achievements can provide an important reference for improving the noise vibration harshness of hybrid electricvehicles.