Dymola Resource Center

This paper describes some usage examples of Dymola within Toyota. Dymola has been used in many divisions, including Engine, Drivetrain, and Chassis. In the Drivetrain division, acceleration performance and noise vibration are being evaluated. In the Engine division, we have constructed an Engine library for Diesel Engine Control. Using the model, we have analyzed behavior of mass flow, pressure, and temperature in all parts of the engine. In addition evaluation of a designed control system was done.

"To construct the drivetrain models, we have been mainly used Dymola. For a simulation package, it is important that it is easy to construct models. It is also important that a model once built is able to be easily re-used. Therefore, Dymola is convenient because it has a drivetrain library, and if the library doesn't contain a model which we need, we can make the necessary model easily."

The HILS (Hardware In the Loop Simulation) is a popular technique to debug control logic of vehicles. Previously, only simplified models could be used to achieve real time performance in the simulations. On the other hand, quite detailed models of engine, drivetrain, hydraulics and brake system were developed with Dymola in recent years. Therefore we would like to use these models also in HILS. However, real time is difficult to obtain for stiff model components, such as the hydraulics, because integrators with fixed step size must be used. With explicit methods very small step sizes are needed to ensure stability. With implicit methods large nonlinear systems of equations have to be solved. Both approaches seem to be not feasible. To improve this situation, the new inline and mixed mode integration technique introduced by Dymola is evaluated for an engine model and results are reported.

In this article, hardware-in-the-loop (HIL) simulation of a passenger car automatic gearbox is discussed. The simulation includes detailed models of the mechanics and hydraulics and less detailed models of the other parts of the car's drive train like its engine, torque converter, differential gearbox, chassis and driving resistances. After a short description of the components to be modeled, special issues of simulating variable structure mechanical systems (coupled frictional elements), simulating hydraulics and simulating in real time with the gearbox control electronics hardware in the loop are discussed. A simulation based, detailed assessment of the dynamics of the gearbox hydraulics show that it might be modeled (under certain assumptions) with fixed causality without major loss of accuracy. Therefore nonlinear systems of equations in the hydraulic parts of the model can be avoided. This enables the usage of a model based on hydraulic component submodels, rather than on overall global dynamics to be used for real time simulations with standard HILsimulation hardware. The article ends with a short discussion of HIL-simulation results and an outlook on future work.

In order to comply with increasing consumer and regulatory demand for improved fuel economy and lower emissions, Ford Motor Company is developing a Hybrid Electric Vehicle (HEV) version of the Escape sport utility vehicle for production in 2003. Since HEVs typically have several different operating modes (e.g. electric launch, active neutral, regenerative braking), an important concern is the fact that each of these modes and the transitions between them lead to minimal driver perceived vibrations. In order to understand how the design and control of an HEV influences what is "felt" by the driver, we need to build models that accurately reproduce the dynamic response of the power-train. In this way, the response for a given mechanical configuration and/or controller design can be evaluated.

A model targeted at prediction of driver perceived vibration was developed and validated against experimental data. However, one unexpected result of this work was to demonstrate that we could take the dynamic model used to reproduce the behavior described previously and, by using some advanced Modelica features, derive a second model that predicts the system efficiency of the transmission without having to create an entirely new model for that purpose. The system efficiency model was also validated against experimental data and showed very good agreement. The result is that rather than spending time creating and maintaining two different models (one for dynamic response and one for system efficiency) we were able to build one on the foundation of the other. Furthermore, we determined it was possible to generate a single model that could describe both types (i.e. dynamic and steady-state) of responses by merely changing the values of a few model parameters.

It is shown how to model and simulate frictional effects present in gearboxes and in planetary gearboxes. This includes modeling of gear wheel stucking and sliding due to Coulomb friction between the gear teeth leading to load torque dependent losses. This allows reliable simulation of, e. g., stick-slip effects in servo drives or gear shifts in automatic gearboxes. It is also discussed how the friction characteristics can be measured in a useful way. The presented models are implemented in Modelica and demonstrated at hand of the simulation of an automatic gearbox.

Models that can be used to analyse the fuel consumption of auxiliary units in heavy vehicles are presented. With the purpose of evaluating the influence from various drive concepts and control principals, a model library is developed in the modelling language Modelica. The library contains a mixture of models developed from physicalprinciples and models fitted to collected data. Modelling of the cooling system is described in some detail. Simulation results are compared with measurement data from tests in a wind tunnel.