Real Time Simulation of Complex Automatic …

1 1 real time Simulation of Complex Automatic Transmission Models Marius B u , Andrei Maciac, Mircea Oprean, Nicolae Vasiliu real time Simulation of Complex Automatic Transmission Models 2 Introduction To manage the function of a vehicle s engine, transmission, and related subsystems, almost all modern vehicles make use of an electronic control system. This powertrain control system continues to become more Complex in order to meet the increased cus-tomer expectations and tightening environmental regulations. The development cycle of electronically controlled mechanical devices can be speed up using hardware-in-the-loop (HiL) Simulation .

2 For powertrains, this replaces tradi-tional testing environments such as real vehicles or powertrain dynamometers that are often expensive, time -consuming, and subject to variability. Modern electronically controlled Automatic transmissions (AT) employ logic features of the implemented software to provide good performance and shift quality over a wide operating range. New control algorithms and calibrations techniques are used to meet permanently in-creasing comfort standards regarding the gearshift of AT. This is a typical application for which the use of HiL Simulation has a big impact. In order to cope with real - time Simulation constrains, only rough models are often used.

3 However studies show that it is possible to use detailed models of modern AT, [7], [1]. Such models allow the testing of electronic control units under simulated conditions that would otherwise be very expensive or awkward to reproduce, for ex-ample high altitude, incorrect settings or changes due to parts wear. For AT an ade-quate physical mechanical model can also provide good efficiency estimation. A high level of modelling of the transmissions permits also to study the influence of comfort improving control strategies ( clutch slipping) on fuel consumption. Supplemen-tary difficulties appear when a detailed model of the Electrohydraulic Control Unit (EHC) is required since the usual hydraulic component models are not adapted for real - time Simulation , [1].

4 This paper aims to present typical modelling of AT and real - time Simulation issues involved in these applications. Models of key components (hydraulic control circuit, clutches, brakes, torque converter etc) adapted for real - time are discussed and their use is integrated in a full powertrain model adapted for comfort and fuel consumption studies. The results presented demonstrate that a real - time Simulation of AT with de-tailed hydraulic control circuit is possible. The highly detailed AT models are developed and tested offline using LMS AMESim (AMESim) a 1D multi-domain Simulation platform.

5 AMESim gen-erates C code that can be use in simulink and by use of real - time Workshop can be downloaded on different HiLS targets. A dspace platform was used in order to evaluate the benchmark problems and to demonstrate the real - time performance of Complex powertrain models. real time Simulation of Complex Automatic Transmission Models 3 real - time Simulation demands To turn an offline plant & control model into a real - time model is necessary to ensure that the plant model runs with fixed step solver. This can make real - time Simulation more challenging than desktop Simulation . Usually some simplifications should be done but with good understanding of real - time needs simplifications can be kept small.

6 Moreover, for a Simulation to execute in real - time , the amount of time spent calculating the solution for a given time step (execution time ) together with the amount of time spent processing inputs, outputs, and other tasks must be less than the length of that time step. It is necessary to leave sufficient safety margin to avoid an overrun when simulating in real - time , figure 1, [6]. Figure 1. The constrains of the step size for real - time Simulation To move from desktop Simulation to real - time Simulation on the chosen real - time hardware, the following items can be adjusted: solver type, number of solver itera-tions, step size, model size and fidelity.

7 The challenge is to find appropriate settings that provide accurate results (results sufficiently close to the results obtained from desktop Simulation ) while permitting real - time Simulation . Recommendations for this process are given in [6]. Base on the authors experience, when using AMESim to develop a powertrain model for real - time applications the following steps are recommended: 1. Build a standard AMESim model and test it with variable step solver; 2. Modify the model considering the specific recommendations for real - time ( use only submodels proven for real - time Simulation , reduce the number of states espe-cially the ones with higher dynamic) and validate the model ; 3.

8 Adjust the parameters in order to work with fix step solver and test it in AMESim; 4. Connect the model with the simulink using AMESim- simulink interface blocks and test the model using the desired fix step solver from simulink ; real time Simulation of Complex Automatic Transmission Models 4 5. Build an appropriate user interface for the real - time application, generate the code for real - time , load it to the real - time platform and connect the interface to the plat-form (if necessary). The first step is not mandatory. It allows testing very detailed models and can be use as a validation tool. It is also recommended if the use of real - time submodels can af-fect the results.

9 If sufficient validation data exist it can be skipped. Prerequisites Typically the development of a plant model for real - time application implies the use of more than one software packages. Today different software packages offer dedi-cated components libraries that can be use for modelling and Simulation of power-trains and many support real - time Simulation (AMESim, Dymola, SimulationX etc). Nevertheless simulink is the preferred environment for control system design and code generation for real - time applications (using real - time Workshop). Different software is needed to control the real - time platform and a supplementary experiment environment can be use.

10 All aspects regarding software compatibility and configurations must be considered before the project is started. It is advisable to firs test every software packages in-volved and the compatibility and interfaces between them. In the studied cases the models were developed in AMESim and exported on a dspace RT platform using real - time Workshop from simulink . Therefore is essential to check the versions compatibility and test the interfaces between: 1. AMESim- simulink ; 2. simulink - dspace ; 3. AMESim- simulink - dspace . Every software developer provides compatibility tables but generally not all the pos-sible combinations are fully tested.