---- WHITE PAPER Vehicle Suspension Analysis CONTENTS Introduction 1 Role of vehicle suspension 2 Motion analysis 2 Motion analysis using COSMOSMotion 3 Real-life example 4-5 Exporting loads to COSMOSWorks 6-7 Automating analysis using COSMOSMotion API 7 SolidWorks Corporation
INTRODUCTION COSMOSMotion is a simulation software package for motion study of any mechanism. Motion study is a term for simulating and analyzing the movement of mechanical assemblies and mechanisms. Motion studies are two types; one is kinematics and the other dynamics. Kinematics is the study of motion without regard to forces that cause it, and dynamics is the study of motions that result from forces. Kinematic simulations show the physical positions of all the parts in an assembly with respect to the time as it goes through a cycle. Dynamic simulation shows joint reactions, inertial forces. This paper mainly deals with the vehicle suspension analysis using COSMOSMotion, and how an automotive designer can optimize their suspension design using COSMOSMotion simulation software package. COSMOSMotion is a perfect simulation tool to perform dynamic and kinematic analysis of any mechanism. Mechanisms are represented as assemblies of rigid components and each component has certain degrees of freedom. Design optimization can increase the value of a product by improving its performance within its operating environment. This paper also addresses how a design engineer can use COSMOSMotion on real time mechanisms like vehicle suspension, and how he can succeed in getting satisfactory results and also saving valuable time and money. The following Fig 1 is CSUN Formula SAE 2005-2006 race car front and back suspension on which CSUN students performed dynamic analysis using COSMOSMotion and COSMOSWorks and they competed with other schools in West competition in Fontana in June 2006. Figure 1 CSUN Formula SAE Race Car Suspension VEHICLE SUSPENSION ANALYSIS no. 1
ROLE OF VEHICLE SUSPENSION / MOTION ANALYSIS MESHING Role of vehicle suspension Suspension is the term given to the system of springs, shock absorbers and linkages that connects a vehicle to its wheels. Suspension systems serve a dual purpose - contributing to the vehicle's handling and braking for safety and driving pleasure, and keeping vehicle occupants comfortable and reasonably well isolated from road noise, bumps, and vibrations. Suspension system is an assembly used to support weight, absorb and dampen road shock, and help maintain tire contact as well as proper wheel to chassis relationship. A vehicle in motion is more than wheels turning. As the wheel revolves, the suspension system is in a dynamic state of balance, continuously compensating and adjusting for changing driving conditions. Several forces affect the tire to road contact of a vehicle. Vehicle dynamics is the study of these forces and their effects on a vehicle in motion. Road isolation is the vehicle's ability to absorb or isolate road shock from the passenger; the degree to which this is accomplished is controlled by the condition of the suspension system and its components. A properly functioning suspension system allows the vehicle body to ride relatively undisturbed while traveling over rough roads. Suspension design will affect the handling of a vehicle. If the design engineer can refine his problem definition to a single objective - or one objective at a time - the optimization process becomes easier. Hence, it is very important to analyze vehicle suspension components before manufacturing. Dynamic analysis has to be performed on a vehicle suspension to analyze their components and also to see how they are going to perform in worst-case scenario. Motion analysis The traditional method of performing dynamic and kinematic analysis of any mechanism is preparing the data, solving the algorithms, which involves the solution of simultaneous equations, and analyzing the results. For a complex mechanism like vehicle suspension shown in the following Fig 2., solving the dynamic equations for motion "by hand" requires intensive calculations, and even with the help of computerized spreadsheet it may take a few hours to get the results and plot the graphs. One can develop a program using software to solve the dynamic equations of motion, but if the geometry of any component changes then the whole program has to be changed again. A design engineer can successfully overcome these problems in motion analysis by using COSMOSMotion simulation software. VEHICLE SUSPENSION ANALYSIS no. 2
MOTION ANALYSIS USING COSMOSMOTION Figure 2 CSUN FSAE Race Car suspension model If the engineer selects too many variables, or too few, the effectiveness of the analysis can be hampered. Motion analysis using COSMOSMotion COSMOSMotion is a simulation software package to analyze and optimize a mechanism, and it is embedded in the SolidWorks interface. It enables engineers to model 3D mechanical systems as "virtual prototypes" and can produce kinematic and dynamic results such as acceleration, joint reaction forces, and inertial forces. COSMOSMotion helps to reduce the number of physical prototypes needed in product development. And also, an engineer will be able to increase the efficiency of the product and can eliminate the expense caused by design changes late in the manufacturing process. COSMOSMotion speeds up the process by reducing costly design change iterations. It enables an engineer to design and simulate moving assemblies so that you can find and correct design mistakes before building the physical prototypes. It also calculates the loads that can be used to define load cases for structural analysis. Motion data, such as forces, accelerations, velocities, and the exact locations of joints or points on geometry can be extracted using COSMOSMotion. Forces that result from motion are of particular interest because they can be used as loads for FEA of individual members in COSMOSWorks environment. Typically, the highest load for a cycle is used to perform a linear static Finite Element Analysis (FEA) of critical individual components of a mechanism. Integration of SolidWorks (solid modeling), COSMOSMotion(motion simulation), and COSMOSWorks (FEA) software can greatly streamline this process - especially important when studying design alternatives, where many analyses are required. VEHICLE SUSPENSION ANALYSIS no. 3
- REAL-LIFE EXAMPLE The two most frequently used methods of shape optimization are gradient search and design of experiments (DoE). Real- life example CSUN FSAE 2005-2006 RACECAR Every year CSUN students build their own style Formula racecars. The design and fabrication of the FSAE racecar takes place over a period of nine months and is used as a training ground for young and innovative engineers in preparation for the engineering industry. This project employs the skills required in an engineering firm, from the design process to the fabrication process, where each step is always taking cost, ease of manufacturing, time, and safety into consideration. Designing is done with the help of CAD tools such as SolidWorks, COSMOS and other CAD tools. Modelling of the car components is done using SolidWorks and component analysis is done using COSMOS. CSUN FSAE 2005-2006 racecar suspension was analyzed and optimized using COSMOSMotion. A complete force analysis of CSUN Formula SAE 2006 racecar suspension was performed with help of SolidWorks, COSMOSMotion, and COSMOSWorks. Initially an Excel macro was created to analyze the road load conditions in worst-case scenario, including (1) accelerating, (2) braking, (3) cornering with bump and braking, and (4) cornering with bump and accelerating. Vehicle suspension components were assembled using SolidWorks and their appropriate joints were defined to create a mechanism using COSMOSMotion simulation software. Then, the road loads were applied to the suspension assembly in order to analyze the reaction forces between suspension components such as A-arm brackets, uprights, pittman arm, shock mount, and pushrods. VEHICLE SUSPENSION ANALYSIS no. 4
- REAL-LIFE EXAMPLE To analyze the vehicle suspension using COSMOSMotion, an engineer needs to know: 1. Each joint in the mechanism will have how many degrees of freedom 2. Spring stiffness and damping force in the shock absorber 3. Which parts are moving and which parts are fixed. 4. Input loads such as normal force, lateral force and longitudinal force. Figure 4 Front suspension model Sensitivity studies can point the engineer to the most significant parameters as well as the range of values having the most impact on the objective. First step in suspension analysis using COSMOSMotion involves defining all the components in the suspension assembly model as moving or grounded parts accordingly. After which the joints and joint primitives are generated automatically from SolidWorks assembly mates. For example, a spherical joint can be generated automatically from SolidWroks assembly mate such as point-to-point coincident joint. Next step involves adding a spring, either torsional or translational according to the design requirement, and defining the spring stiffness and also adding damper in the Shock cylinder and defining the damping force. And finally, applying the calculated road loads in worst - case scenario (1) cornering with bump and braking, and (2) cornering with bump and accelerating. Ability of COSMOSMotion to detect and fix interferences in the assembly model without switching between software is one of the primary benefits of integrating COSMOSMotion and SolidWorks. The motion of a particular joint or surface of point on component can be plotted as a line. After running the simulation one can plot all the results like reaction forces in three directions on each joint as shown in the following Fig. VEHICLE SUSPENSION ANALYSIS no. 5
EXPORTING LOADS TO COSMOSWORKS Figure 4 Rear suspension results using COSMOSMotion The engineer who undertakes optimization will get the best value out of the technology by performing optimization in the early stages of the design process. Exporting loads to COSMOSWorks Forces that result from COSMOSMotion can be used as loads for structural analysis of individual components. COSMOSMotion allows you to export reaction force results in a form suitable for import by many Finite Element Analysis (FEA) programs, where one can predict the component stresses, deflections and Factor of Safetry check. COSMOSWorks is a FEA tool, which is also embedded in SolidWorks. One can export COSMOSMotion reaction force results of a vehicle suspension component to COSMOSWorks to perform FEA. All COSMOSMotion entity property dialog boxes contain an FEA tab. On each of these tabs, one can select faces or edges on the part where the entity is attached. These faces and/or edges become the bearing surfaces for the forces calculated by COSMOSMotion. When the force data is transferred to the FEA application, the forces and moments are distributed onto the selected faces and edges. One can choose to define the bearing surface at the time you create an entity or at the time you export the results to the FEA application. Once the bearing surface is defined, it is used for subsequent transfers to the FEA application. An engineer can perform FEA analysis on each vehicle suspension component by exporting loads that result from COSMOSMotion. The following figure shows upright component of racecar suspension on which FEA has been performed using COSMOSWorks by exporting loads that result from COSMOSMotion, and the component has been optimized by reducing its weight. VEHICLE SUSPENSION ANALYSIS no. 6
EXPORTING LOADS TO COSMOSWORKS Engineers planning to use optimization as a tool for improving designs and products need to clear their minds of any pre-conceived ideas of what constitutes "optimal." The reaction forces on the upright component of suspension assembly after running the simulation are shown in the figure below. When loads are exported from COSMOSMotion to COSMOSWorks, the loads and their directions will be defined automatically in COSMOSWorks as shown in the figure. Mesh the component and run the design scenario. The FEA results can be displayed as shown in the figure below. Automating analysis using COSMOSMotion API An Engineer can automate the vehicle suspension analysis using application programming interface. SolidWorks supports application programming interface as well as COSMOSMotion. A macro can be developed using COSMOSMotion, which can automate the motion simulation. By running a macro one can run the simulation, add joints, and all those things which you can do manually in COSMOSMotion. And also you can connect COSMOSMotion to the spreadsheet using API, where you can input all the forces in spreadsheet and run the program all the results will be displayed in spreadsheet. VEHICLE SUSPENSION ANALYSIS no. 7
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