Extending the inverse vehicle propulsion concept - To improve simulation performance

Abstract: Drive cycle simulations of longitudinal vehicle models is an important toolfor design and analysis of power trains. On the market today there are severaltools for such simulations, and these tools use mainly two differentmethods of simulation, forward dynamic or quasi-static inverse simulation.Forward dynamic simulation is capable of describing the dynamic behaviorof a system to a high level of detail, but suffers from long simulation times.On the other hand, quasi-static inverse simulations are very fast, but lack theability of describing additional dynamics in a good way. Here known theoryfor stable inversion of non linear systems is used in order to try to combinethe fast simulation times of the quasi-static inverse simulation with the abilityof describing the dynamics as in the forward dynamic simulation. Thestable inversion technique together with a new implicit driver model forms anew concept, inverse dynamic simulation. Using this technique the need todevelop dedicated inverse models is reduced, and it is shown that a largeclass of models that can be simulated in forward dynamic simulation alsocan be simulated in inverse dynamic simulation. In this respect, three powertrainapplications are used that include important dynamics that can not behandled using quasi-static inverse simulation. The extensions are enginedynamics, drive line dynamics, and gas flow dynamics around dieselengines. These three cases also represent interesting mathematical propertiessuch as zero dynamics, resonances, and non-minimum phase systems,i.e. unstable zero dynamics. The inversion technique is demonstrated on allthree examples, and the feasibility of inverse dynamic simulation of thesesystems is shown. Moreover, using the three examples, inverse dynamicsimulation is compared to forward dynamic simulation regarding simulationset-up effort, simulation time, and parameter-result dependency. It is shownthat inverse dynamic simulation is easy to set up, gives short simulationtimes, and gives consistent result for design space exploration. This makesinverse dynamic simulation a suitable method to use for drive cycle simulation,and especially in situations requiring many simulations, such as optimizationover design space, powertrain configuration optimization, ordevelopment of powertrain control strategies.