Frontloading in Transmission Concept Optimization

Transmissions today are frequently installed in a range of different vehicles and vehicle variants, with clearly differing loads in each specific case. It is therefore increasingly important to perform detailed simulations of future operating scenarios under real driving conditions at an early point in the development process. IAV has therefore further refined the models of its Velodyn (Vehicle Longitudinal Dynamics) tool to compute bearing or cogwheel loads already during longitudinal dynamic cycle simulation in the concept phase.

“Today it is not a rarity for transmissions originally developed for a conventional car to be put into a completely different vehicle – such as a sports car or a pick-up, or even in a nonroad vehicle”, explains Dr. Klaus von Rüden, IAV Head of Department for Powertrain Concepts and Transmission Electronics. “But this can be doomed to fail if the loads occurring in these other vehicles are too high for some of the transmission components.”

IAV’s experts have faced this challenge several times in recent years, and therefore decided to perform detailed Velodyn simulations for different applications already in the concept phase. In the traditional approach, transmission loads are not computed until the transmission design phase and validated during endurance testing. Now, “frontloading” with Velodyn permits initial estimates already at the start of the V-process so that the design engineers are given valuable time to react to changes in requirements. The new approach with its early, consistent use of simulation also makes an important contribution to the digitization strategy of the automotive industry.

Together with IAV’s hardware designers, Dr. Klaus von Rüden and the simulation team have worked with Dr. Felix Matthias, IAV Technical Consultant for Powertrain Simulation and Drivability to develop new models permitting numerous predictions: which forces occur in the transmission with which frequency? Which application scenarios result in peak loads? Is there excessive load on bearings or clutch linings? “Already in the concept phase we can therefore see the various operating scenarios for the transmission under real-life conditions”, says Matthies. “Such precise knowledge of every application is crucial for system optimization. For example, the simulations may indicate a need for a stronger bearing or additional clutch disks.” The method is also attractive because it reduces the need for additional validation, thus helping to cut material consumption and production costs.

Besides detailed information about the powertrain components, Velodyn also needs to know the essential parameters of the model. These include, for example, vehicle mass, characteristics of the combustion engine, road resistance, maximum torque and wheel radii, which are also easy to vary if necessary. The tool uses these inputs in the RDL simulation mode to reproduce realistic situations, including extremes such as racetrack conditions or driving on sand with the wheels held at full steering lock. In the end, the developers obtain detailed information about bearing forces, efficiency levels of individual components and specific load spectrums.

Velodyn has been extended from a purely longitudinal dynamic tool to a two-track model and now also supplies transversal loads, such as that on the differential when driving round bends. “This is also important for studies in the RDE context”, says von Rüden. The complex RDE test cycles also include bends, while in the past the vehicle simply had to run straight ahead on the roller dynamometer. Velodyn is now therefore also equipped for RDE.”

The new features have been available since early 2016. They have already proven their worth in several customer projects and are currently being put in the Velodyn library, where they will be available in future to all users. The tool can be purchased from the IAV partner Exothermia. “Velodyn therefore offers a real USP which will certainly be of interest to many of our customers”, says Matthies. “It also once again demonstrates our leading position in the area of transmission models, with the possibility of transmission calibration from the desk.”