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.

2 The development cycle of electronically controlled mechanical devices can be speed up using hardware-in-the-loop (HiL) Simulation . 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.

3 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. 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.

4 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]. This paper aims to present typical modelling of AT and real-time Simulation issues involved in these applications.

5 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.

6 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.

7 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. 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.

8 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. 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 .

9 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. Adjust the parameters in order to work with fix step solver and test it in AMESim; 4.

10 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.