Extending the Inverse Vehicle Propulsion Simulation Concept -To Improve Simulation Performance

Drive cycle simulations of longitudinal vehicle models is an important tool for design and analysis of power trains. On the market today there are several tools for such simulations, and these tools use mainly two different methods of simulation, forward dynamic or quasi-static inverse simulation. Forward dynamic simulation is capable of describing the dynamic behavior of 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 the ability of describing additional dynamics in a good way. Here known theory for stable inversion of non linear systems is used in order to try to combine the fast simulation times of the quasi-static inverse simulation with the ability of describing the dynamics as in the forward dynamic simulation. The stable inversion technique together with a new implicit driver model forms a new concept, inverse dynamic simulation. Using this technique the need to develop dedicated inverse models is reduced, and it is shown that a large class of models that can be simulated in forward dynamic simulation also can be simulated in inverse dynamic simulation. In this respect, three powertrain applications are used that include important dynamics that can not be handled using quasi-static inverse simulation. The extensions are engine dynamics, drive line dynamics, and gas flow dynamics around diesel engines. These three cases also represent interesting mathematical properties such as zero dynamics, resonances, and non-minimum phase systems, i.e. unstable zero dynamics. The inversion technique is demonstrated on all three examples, and the feasibility of inverse dynamic simulation of these systems is shown. Moreover, using the three examples, inverse dynamic simulation is compared to forward dynamic simulation regarding simulation set-up effort, simulation time, and parameter-result dependency. It is shown that inverse dynamic simulation is easy to set up, gives short simulation times, and gives consistent result for design space exploration. This makes inverse dynamic simulation a suitable method to use for drive cycle simulation, and especially in situations requiring many simulations, such as optimization over design space, powertrain configuration optimization, or development of powertrain control strategies.