Study On Modeling Of Quasi-instantaneous Engine Output Torque And Mounting Load Based On Indicator Diagram

High-quality dynamics model for dynamic load simulation is one of the trends ofvehicle dynamics model research and development. Internal-combustion engine generateshigh frequency excitation during operation, which may cause dynamic response in fullvehicle. However, the most widely-used internal-combustion engine model in vehicledynamic simulation is steady-state model, which can’t describe the fluctuation of enginedrive torque and mounting load along with the change of crankshaft angle. Consequently,this article concentrates on the modeling of instantaneous engine drive torque output andpowertrain mounting load in order to improve the dynamic performance of the vehicledynamic.Main purpose of this article is to build the quasi-instantaneous engine dynamics modelbased on indicator diagram, which was able to compute the dynamic output of crankshaftspeed, drive torque and powertrain mounting load in720degrees of crankshaft rotation cycle.It is important that this engine model is suitable to full vehicle simulation use. Andmeanwhile, the model should have the capability of real-time simulation for its further use indriving simulator.Main research contents of this article are as follows:1. Study on quasi-instantaneous engine dynamics model. Piston-connecting rod systemand engine block model have been built, and the coupling between the two parts is taken asone-way-coupled model.To satisfy the requirement of real-time simulation, dynamically equivalentpiston-connecting rod model was built. The connecting rod is simplified to spring anddamper, and its mass is distributed to piston and crank, which makes the piston translationand the crank rotation uncoupled. This model can be solved much faster than traditionalmulti-body dynamics model because rigid differential-algebraic equations will not bebrought out. Based on multi-body dynamics, Newton-Euler equations of engine blockrelative to moving reference frame are derived, which can make the calculation of mountingload more accurate when the engine model is used in full vehicle dynamics simulation.2. Study on key issues in quasi-instantaneous engine modeling, which are high speed algorithm of indicator diagram interpolation, quasi-instantaneous friction model and enginemounting model respectively.High speed algorithm of indicator diagram interpolation has been used to calculate theinner pressure. Interpolation interval index is recorded when interpolation，which helps tofind the suitable interval rapidly in next time step. This algorithm can obviously improve thecalculation speed for more than ten times especially for large amount of data. The modelingof quasi-instantaneous engine friction can reflect the relationship of frictional force andtorque and the crankshaft angle. The coefficients of the friction model are identified based onthe steady-state friction torque. Engine mounting model has been built, and the parameters ofMaxwell-based mounting model are identified according to its dynamic stiffness curve.3. Verification of quasi-instantaneous engine model and its application. The real-timecalculation performance and model accuracy have been verified. The model also has beenembedded into full vehicle dynamic model.This quasi-instantaneous engine model has been realized using C code. It completelymeets the real-time requirement for reason that a10seconds simulation only needs0.93seconds for calculation. Verification under steady state conditions: Another inlinefour-cylinder engine model is established in Adams/Engine module. By comparing the twomodels, the simulation results are in consistence with each other very well. Simulation undernon-steady state conditions: Quasi-instantaneous engine dynamics model simulates undernon-steady state conditions, such as variation of load torque, variation of throttle percentageand not completely combustion, which certificated that the model has non-steady simulationcapability. Full vehicle dynamics simulation: The engine model is embedded into full vehicledynamics model and some cases like straight-line acceleration condition has been simulated.Dynamic effect caused by quasi-instantaneous drive toque and mounting load output appearsin full vehicle dynamics simulation.