Explicit Simulation of Dampened Starter System using Altair Radioss Siva Sankar Reddy. A Sr. Engineer CAE, PES Valeo India Private Limited Block - A. 4th Floor, TECCI Park, Old No.285, New No.173, Rajiv Gandhi Salai, (OMR) Sholinganallur, Chennai - 600 119. Thangavelu.Chinnamuthu Engineering Manager, PES Valeo India Private Limited Block - A. 4th Floor, TECCI Park, Old No.285, New No.173, Rajiv Gandhi Salai, (OMR) Sholinganallur, Chennai - 600 119 Abstract Gear Reduction Starter Motor is used in automotive engine starting system. The starter motor has many sub assemblies and Reduction gear unit is critical, considered for this simulation. Reduction gear unit consists of Ring gear, Ring gear support, Satellite gear, Cover, Sun gear and dampers. Simulation is done to understand the behavior of dampers and Impact load on gear tooth with and without dampers. Both tetrahedral second order elements and hexahedral elements were used depending upon the complexity of the geometry. Numerous contacts were defined using Type 7 contacts. Simulation was done using Altair Radioss 10. Preprocessing was done using Altair HyperMesh 11.0 and Post processing is done using Altair HyperView 11.0. Introduction Starter Motor (DC Motor) is used in automotive applications to assist starting of an engine. The Gear Reduction Starter Motor has an inbuilt reduction gear unit that helps to increase the output torque compared to actual motor torque however the output speed be less than Motor speed (Armature speed). While starting an engine, the gear box unit will be subjected to very high impact load momentarily due to initial friction. In order to reduce the impact of momentary peak load, arrangements made to allow the ring gear to rotate for a limited angle that reduces the momentary peak load. The dampers are used to allow ring gear rotation by observing the energy generated (compression) and reduce the impact load on ring gear of reduction gear mechanism. Process Methodology (details with figures) In the study presented in the paper, the ring gear assembly consists of 20 components including ring gear, Ring gear support, Satellite gear, Armature shaft, dampers, Cover, screws and brackets. Tools used Preprocessing: Altair HyperMesh 11.0 and Altair Hyprecrash 11.0 Solver: Altair Radioss Block 100 Solver Post processing: Altair HyperView 11.0 and Altair HyperGraph 11.0 FE Modeling: Regular shaped geometries were generally modeled using Hexahedral elements and Complex molded components were modeled using Tetrahedral elements. First order elements are generally used in the concept evaluation stages while second order elements are used in the validation of final design. HyperMesh 11.0 is used for preparing the FE Model of the individual components and the assembly. The FE Model is shown in Figure 1. Simulation Driven Innovation 1
Figure 1: FE Assembly Model Figure 2: FE Model Individual parts. Simulation Driven Innovation 2
Interface Definition: The contact surfaces needed for the accurate definition of the interfaces are created in HyperCrash using self Impact option. Contact Interfaces of Type 7 is created and friction is modeled by choosing the coulomb friction option. Depending upon the contact status of the interface, appropriate minimum distance for impact is carefully chosen. Material Model Definition MAT42_Ogden properties are used for dampers, Polyamide properties for ring gear support and steel properties for remaining parts. Loading conditions Torque and velocity is applied through the rigids. Figure 3: Loading conditions. Control Cards and Engine Settings Appropriate control cards for controlling strain formulation are used to ensure that the stable time increments for the solution are not abruptly low. All required output controls are activated to capture stress, plastic strain and deformation at desired time intervals. History output of Global variables like Internal energy, Kinetic energy, Hourglass energy and Total energy are requested to monitor the accuracy of the solution. Appropriate frequencies are defined for writing out results of field variables, global variable and, restart files. Eight processors are used for the engine calculation using HP-MPI in Windows 64 bit operating system Simulation Driven Innovation 3
Results & Discussions Two simulations were done to understand the importance of dampers and its properties. The maximum deformation in the dampers due to the impact was seen in the simulation, Along with that the deformation stress, contact forces and resultant torque is extracted. Some of the critical results observed are presented in the Figures. Deformation in the dampers. Due to force exerted by planet gears ring gear is rotating and compressing the dampers. The maximum angle from the reference position is nearly 11.2. By changing the damper properties, The ring gear angular displacement came down to nearly to 0.25. Figure 4 Deformation of dampers. Contact forces in the ring gear. The Max. force acting on ring gear handle is nearly 115N. This peak force is showing at time of max. damper compression. By changing the damper properties, The force acting on ring gear handle increased to nearly to 250N. Figure 5 Contact forces in the ring gear handle. Simulation Driven Innovation 4
Stresses in ring gear handle. Taking the time history of stress showing in root of ring gear handle, At the initial time of impact stress is going in the range of 220MPa, then its reducing considerably as the plot shown. By changing the damper properties, Max. value showing don t show any significant change. Max. value is 250MPa in this case. But the stress is not reducing to lower level as it is showing in with Ogden properties Figure 6 Stresses in the ring gear handle. Benefits Summary User Friendly mesh definition methods in Altair HyperMesh 11.0 have resulted in reducing the preprocessing time considerably. Ease of defining contact, User friendly Penetration detection and correction methods in Altair HyperCrash 11.0 has also helped in a reduction of time further. Overall there is approximately 20% of preprocessing time reduction. The revolutionary Token based Altair licensing ensures that the engineer can prepare a new orientation model in Altair HyperCrash when the Radioss engine solution for another orientation is in progress or read results of a calculation in HyperView or HyperGraph that is already completed. This means more productivity in Pre and Post processing which is commonly missing in other commercial tools. Challenges Key challenges in undertaking this project are listed below a) Selection of appropriate element type, size and control cards for element properties to ensure a manageable stable time increment for solution. b) Resolution of initial penetration in contact interfaces. c) Arriving at an optimal calculation time (total time of impact simulation) to ensure appropriate stabilization of Global variables (Internal and Kinetic energy) and minimize calculation errors. Simulation Driven Innovation 5
Conclusions Explicit simulation of dampened starter system using Altair HyperWorks Tools and Altair Radioss solver has given a considerable confidence to the Research and development team in the ability to predict the robustness of the design at the early phase of product development and identify improvement opportunities if any for future concepts. ACKNOWLEDGEMENTS The authors would like to thank Mr.Sriram.G, R&D Director, Valeo India Private Limited for his constant support in documenting this study and sharing it with the CAE community in the Automotive Industry. [1] Altair HyperWorks11.0 Online documentation. REFERENCES Simulation Driven Innovation 6