Renault applies model-based systems engineering to dual-clutch transmission

  • 08-Oct-2014 01:05 EDT
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Renault is equipping its conventional vehicles with a new seven-gear dual-clutch transmission, developed by Getrag.

Car manufacturers are facing various and sometimes contradicting constraints such as energy efficiency, high performance, driving comfort, reliability, and safety. In a global context, they must also adapt driveline designs to different markets. Therefore, Renault must handle a variety of powertrain designs. Moreover, due to increasingly intelligent systems, mechanical and controls system design cycles are more and more linked. A common system mock-up is needed.

Renault has implemented model-based systems engineering (MBSE) to manage these challenges as well as to reduce development cycle and costs. With MBSE, design and integration problems are solved earlier, the number of prototypes and test benches are reduced, and cross-team collaboration is improved. The MBSE approach allows Renault to evaluate, throughout the development phases, the key attributes of the complete vehicle including the engine, transmission, actuators, and chassis.

Renault recently extended its MBSE approach to include a new dual-clutch transmission (DCT) and controls strategies validation and optimization.

The DCT, developed by Getrag, is being integrated into C-segment vehicles such as the Renault Mégane or Scenic, and will be widely applied to other vehicle ranges. The new DCT includes seven gears. Wet clutches allow for increased torque capacity up to 300 N•m (221 lb•ft).

The DCT enables gear pre-engagement when another gear is already engaged and drives power. The gear shifting is limited to clutch switching, without significant engine torque reduction. It makes the whole gear change faster, smoother, and more comfortable than a standard automated manual transmission. The engine control unit just needs to manage a slight torque drop by controlling the fuel injection in diesel engines or spark advance in gasoline engines.

The internal DCT command relies on electrohydraulic actuation for clutches and electromechanical actuation for shifting gears. The electrified command decreases the gearbox’s global power consumption, and it is mandatory when gears are shifted without available engine power (for instance, stop-start applications).

To address different steps of the design V-cycle, Renault must carry out numerous analyses to integrate the gearbox with the various engines and chassis. To cope with multiple simulations addressing different levels of assumptions, Renault has opted for LMS Imagine.Lab Amesim software from Siemens PLM Software as the simulation platform for multi-domain modeling. Using LMS Amesim, various levels of models can be built depending on user constraints and needs: parameters availability, level of details and accuracy, fast simulation constraints, real-time capabilities, etc.

For the DCT project, Renault has used two levels of models addressing the complete drivetrain:

• Level one model: actuators are assumed to be ideal (excepting delays). This model remains simple and accelerates simulations for controls development and validation. It can be used for real-time applications, such as hardware-in-the-loop or software-in-the-loop to help software development.

• More detailed model: mechanical actuators geometry (barrels, connected finger, etc.) is replicated in the model to accurately compute contact forces between components. Main lines and consumers are included within hydraulic circuits that are pressurized by electropumps for clutch actuation. The speed of electropumps is regulated by the control logic to control pressure on the clutch pistons. This model was built to perform deeper analysis related to transmission actuation control and design.

These models help engineers understand the power flows between all subsystems and components as well as some drivability aspects.

Two types of validation were performed to demonstrate the models’ capabilities and accuracy:

• Functional validation confirms very simple scenarios such as correct gear shifting and providing the right actuators responses to the requests.

• Experimental validation compares measurements and simulation results with various variables such as gearbox in-shaft speeds, side-shafts torques, vehicle longitudinal acceleration, engine speed or actuators positions.

Functional model validation is an important stage in the modeling workflow. This step makes sure that the system will have the right type of behavior and functionality. Then, model correlation with experimental data lets Renault check simulation capabilities.

System simulation is used at Renault throughout the V-cycle for different applications. At the beginning, system simulation is applied to select the best system architecture and evaluate how a solution helps answer customer requirements. Then, simulation is used to evaluate high-level controls laws as well as calibration of actuator regulations to estimate the influence of different controls calibration on the gear shifting quality.

For the DCT project, approximately 60 requirements have been translated into scenarios. Then, the scenarios were simulated to validate virtually that the system and its controls fulfill the requirements. This early evaluation enabled Renault to isolate, understand, and solve several minor bugs and logic design issues that could have become critical if identified later on. Moreover, prototype testing can be accelerated by applying simulation during the pre-validation stage of the controls logic.

In addition, MBSE helps engineers quickly evaluate new designs or controls logic improvements, for example, to reduce fuel consumption with a good balance between the NVH response and drivability.

This article was written for Automotive Engineering by Vincent Talon of Renault and Nicolas Sabatier and Patrice Montaland of Siemens PLM Software.

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