【作者】 黄粉莲；

【导师】 纪威；

【作者基本信息】 中国农业大学 ， 车辆工程， 2014， 博士

【摘要】 营运货车在促进国民经济和社会发展的同时,也给人类所面临的能源危机和环境污染问题带来严重的威胁。动力传动系统是车辆正常行驶的动力源,其性能的优劣直接影响汽车的动力输出、燃油消耗和污染物排放。动力传动系统的仿真、匹配优化是提高动力传动系统全局效率、改善经济性及排放性的重要技术措施。针对行驶工况下货车动力传动系统参数匹配不佳及瞬态工况下柴油机性能恶化等问题,本文建立动力传动系统工作过程仿真模型,开展了稳态、瞬态工况下涡轮增压柴油机性能预测、动力传动系统动态过程仿真、标准行驶工况下整车性能仿真及优化等研究工作。建立基于Matlab/Simulink的涡轮增压柴油机系统工作过程实时仿真模型,对稳态工况下发动机动力性、经济性、碳烟排放、热NO与瞬发NO排放等进行预测。对进气流量计算平均值模型进行比较分析,在充分考虑EGR率、残余废气系数及充量系数影响的基础上,对原始进气流量模型进行修正,通过仿真分析并结合试验数据进行验证,确定了最佳的进气流量计算模型。通过详细分析传动系统各部件间的动力学关系,建立动力传动系统转矩平衡方程,采用逆向推理法制定了自动变速器动态三参数最佳动力性和最佳经济性换档规律,利用有限状态机Stateflow对自动变速器换档逻辑控制进行设计,仿真分析了货车载重变化对换档规律的影响及车辆加速与制动过程的动态响应特性。建立涡轮增压柴油机系统瞬态过程及整车动态性能仿真平台,对柴油机瞬态响应及瞬态工况下的燃烧、NO排放特性进行预测,仿真分析了发动机稳态、瞬态工况下摩擦转矩变化规律。对整车空载原地起步连续换档加、减速过程进行仿真,分析了动态过程发动机转矩、转速、曲轴角加速度、汽车加速度、车速及档位随油门开度变化的情况。在标准行驶工况下对样本车辆循环百公里燃油消耗、PM及NO排放进行仿真,通过分析车辆主要设计参数对车辆性能的相对敏感性,提出一种基于敏感性系数确定优化指标权重系数的方法,以标准行驶工况下车辆循环百公里燃油消耗、PM及NO排放为优化目标,对传动系统的传动比进行优化设计。优化后车辆经济性、NO排放有所改善,PM排放有较大幅度降低。更多还原

【Abstract】 For a long time, commercial trucks have greatly promoted economic and social development, but meanwhile, they have caused serious environmental pollution and exacerbated energy crises. Powertrain system is the lifeline for the vehicles normal traveling. Therefore, the performance of powertrain has a direct impact on the power output, fuel economy and pollutant emissions of vehicles. In recent years, the simulation, matching and optimization of powertrain system has become the researching focus since it’s an essential solution to improve the global efficiency of powertrain and reduce the fuel consumption and pollutants.To predict the performance and pollutant emissions of vehicular turbocharged DI diesel engines during both steady-state and transient process, firstly, a zero-dimensional thermodynamic real time simulation model which based on the filling and emptying method was developed to describe the working process in cylinder. The thermodynamic model takes into account all the engine subsystems viz. turbocharger, intercooler, fuel pump and speed governor. In order to estimate the transient performance more accurately, the Two-Vibe curve model was adopted to simulate the actual heat release rate and fuel burning speed. In addition, the incomplete combustion was taken into consideration. Furthermore, the convective heat transfer rate to the combustion chamber walls was simulated through the heat-transfer coefficient with transient correction. Subsequently, both thermal and prompt NO mechanism were applied to predict NO emissions, and the extended-Zeldovich mechanism and overall reaction rate theory were adopted to simulate the net formation rate of NO. What’s more, the optimal mean value model of air mass flow calculation was determined via comparison various mathematical models of air mass flow and comprehensive optimization.Secondly, the torque balance equation that takes into account all the drag force was established based on the detailed analysis of dynamic relationship between the components of powertrain system. Then gear shifting strategies was optimized for fuel economy and maximum power, and the automatic transmission shift logic was controlled by using finite state machine of Stateflow. Study focused on the evaluation of vehicle performance, and particular attention was given to the engine behaviors under transient conditions, dynamic response characteristics of vehicle acceleration and braking process.Thirdly, according to crankshaft torque balance based on the conservation of angular momentum principle, the instantaneous values of engine speed and angular acceleration were simulated. Specifically, the engine indicated torque that includes the contribution of gas and reciprocating inertia forces of all cylinders was calculated according to the instantaneous cylinder pressure and engine dynamics. The friction torque of diesel engine was calculated through a detailed analytical model, which includes the contribution of piston rings assembly, loaded bearings, valve train and auxiliaries, and describes the non-steady profile of friction torque during each cycle. Moreover, the load torque was determined via the torque balance of powertrain system.Finally, all above models were integrated and a simulation platform of the entire vehicle system was established based on the Matlab/Simulink. Using a step input signal as the step throttle (fuel pump rack position) change, and then run the model to mimic vehicle real transient process under various (vehicle) speeds and gear. The validation of the model was done through comparison of the simulation results with measured values. Fortunately, the simulation results are quite in line with the actual situation, it’s showed that the design of model is reasonable and accurate.To estimate the engine fuel consumption and pollutant emission under real driving conditions, the vhehicle model was simulated based on the standard driving cycle. The simulation results show that the acceleration transient events and the related turbocharger lag phenomena significantly contribute to the cycle cumulative emissions and fuel consumption. Through the sensitivity analysis of fuel consumption and pollutant emissions, estimating the overall impact of design parameters on the fuel consumption and emission performance. The main factors include the vehicle weight, tire rolling resistance, aerodynamic drag and driveline configuration. Studies also indicate that it is difficult to change each of these parameters to reduce the fuel consumption, NO and PM emission simultaneously. Eventually, optimizing the transmission ratio for fuel economy and emissions based on the the sensitivity coefficients. Consequently, the results of this study will be greatly helpful to predict and analysis the economy performance and pollutant emissions of commercial trucks and provide a useful reference basis for the design and optimization of powertrain system.更多还原