Research On Modelling And Evaluation Of Vehicle Dynamics For Hardware-in-the-loop Simulation

With the rapid development of over one hundred years,the vehicle has evolved from a simple mechanical system to a mechatronic system and a cyber physical system.The vehicle performance has been greatly improved,while the complexity of the vehicle also increases doubly,and the vehicle matching,calibration and integrated development become more difficult.Using advanced simulation technologies to reduce or even substitute physical assembly tests is one of the major trend in the vehicle product development.In practical application,the transient processes of some systems,assemblies and components are hard to model in real time currently,such as hydraulic,pneumatic,engine combustion processes et al,pure model simulation is still hard to completely substitute the physical assembly tests.During the product development processes,the component suppliers hope to carry out the vehicle performance matching tests of the physical assemblies and components earlier,without having to wait for the prototype manufactured,to reduce the development risk.After decades of development,the vehicle manufacturers have formed their own vehicle development platform.They can continue to use most of the mature physical assemblies and electronic control units when developing new cars,and the major task is to optimize and match with the new car performance and parameter calibration.Currently,the international automobile industries are committed to using hardware-in-the-loop technology by embedding the physical systems,assemblies,components and electronic control units into the vehicle model to conduct vehicle product development,which is one of the current research hotspots.The hardware-in-the-loop technology has gradually extended from the controller hardware in the loop to the mechanical hardware in the loop,and developed to the hardware in the loop driven by the simulator.By directly embedding into the dynamic test rigs of real objects,the inaccurate modelling problems of the transient process of some assemblies and components can be effectively solved,and the transient process of the vehicle can be simulated with higher fidelity.Component suppliers can carry out vehicle performance matching tests for real objects more accurately and earlier.The vehicle manufacturers can optimize and match the new car rapidly based on physical assemblies,electronic control systems and the new car model,and the new car can be updated and upgraded rapidly to the market.Combined with the driving simulator,most objective and subjective evaluation of vehicle performance tests in the late development cycle can be conducted in the driving simulator in advance.The assemblies as well as components can be tuned,and the electronic control systems can be validated and calibrated in various complex environments,which greatly shorten the development cycle and reduce development costs.During the development processes of the hardware-in-the-loop simulation,there is a need from industry that the physical systems,assemblies and components can be in the loop simulation in various levels,however,it is found that the model modularization of the current commercial softwares of real-time vehicle dynamics is mainly at system level,which is hard to close the mathematical modual in the model corresponding to various level hardwares on demand.When certain physical electronic control system is needed to be calibrated,the simulation model is required to provide the signals of other electronic control systems which are coordinated with it.For example,the powertrain electronic control systems and chassis electronic control systems must be calibrated in coordination.However,the existing commercial softwares of real-time vehicle dynamics mainly lack the available electronic control system models.And during the processes of the electric control system calibration and the system,assembly as well as component hardware in the loop simulation tests,it is mainly aimed at the evaluation and optimization of the vehicle transient motion process,while the existing objective evaluation methods for vehicle performance mainly focus on the evaluation of steady-state performance.In this paper,a vehicle real-time dynamics modular modeling method is tried to explore to build a hierarchical real-time dynamics modular model according to the architecture of the systems,assemblies and components defined in the vehicle structure;The modeling of electronic stability control system is chosen as an example to explore and implement an electronic control system modeling program in which the control strategy is accurately modelled and the actuator is functionally modeled.And an evaluation method for vehicle motion transient motion process is tried to propose.The main research contents are as follows:Firstly,a hierarchical real-time vehicle dynamics modular model is studied.In view of the challenge that the automatic derivation of the dynamics equation according to the geometric topological structure of the mechanical system is hard to build a real-time dynamics modular model,in this paper,a modular modelling method is explored based on the compound constraint isolating and decoupling.Four basic dynamics modules including compound constraints,compound bodies,compound positions and compound forces/moments are systematically defined,and the difficult problem of isolating and decoupling of assembly and component models is resolved.The dynamics functions of assemblies and components of each system belong to one of the basic dynamics module defined in the compound constraint isolating and decoupling method.The steering system,travelling system,braking system and powertrain system are isolated and decoupled respectively,and each submodule is modeled.The hierarchical real-time vehicle dynamics modular model is built and applied to the hardware-in-the-loop successfully.Secondly,the digital electronic control system model is studied.In view of the fact that the existing real-time vehicle dynamics models of commercial software are mainly simple functional logic ECU model,the modeling of electronic stability control system is taken as an example to explore and implement a modeling program including the accurate modeling of ECU strategies and the functional modeling of actuators in this paper,and a detailed controller strategy model and functional actuator model of the digital ESC model is built.Thirdly,an instantaneous wheel turn center method for evaluating the vehicle transient motion process is proposed.Considering the tire forces are the original source to produce the vehicle motion,the vehicle motion is a transient response process mainly from the wheel to the body,an evaluation method based on the instantaneous wheel turn center is tried to explore in this paper.Based on the accurate calculation of the instantaneous wheel turn center,the evaluation index named dispersion of instantaneous wheel turn centers is proposed.The results show that the dispersion of instantaneous wheel turn centers can evaluate the vehicle motion transient process more sensitively as compared to the vehicle performance index.Finally,the modular dynamics model is validated.The model simulation results agree well with vehicle field test data.The brake assembly hardware in the loop simulation platform is built,and the modular model can close its model modules corresponding to the physical assemblies on demand.The test rig is driven by the driving simulator,and the virtual proving ground tests are conducted to validate the effectiveness of the digital ESC model.In addition,the instantaneous wheel turn center method is applied to the evaluation of vehicle transient motion processes.The digital model and evaluation method of this paper can be applied to the vehicle hardware-in-the-loop simulation development effectively.