O os-03 cae-simulation_of_power_liftgate_gm


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O os-03 cae-simulation_of_power_liftgate_gm

  1. 1. CAE Simulation of a Power Liftgate Subsystem for an SUV Vishwabharathi M. Santosh K Swamy Umesh Nayaka Senior Engineer, CAE-Closures Closures Lead Engineer, CAE-Closures Senior Group Leader, CAE-Closures Leader GMTCI GMTCI GMTCI Bangalore- 560066 Bangalore-560066 Bangalore-560066 BangaloreAbbreviations:FEA - Finite Element AnalysisDESVAR-Design VariablesDESOBJ-Design ObjectiveDCONSTR- Design Constraints AbstractsThis paper presents the work done on the t typical Liftgate subsystem of a sport utility vehicle (SUV) which has two variants; amanual operated liftgate and a power actuated liftgate, with the liftglass assembly. In addition to the usual loads the manually manuaoperated liftgate experiences, the power liftgate has the power loading exerted by the struts, which are usually higher in magnitude. iences,This loading is a combination of gas strut and actuator loads. A load matrix is developed specific to each vehicle & type of power ssystem used. The matrix will include combinations of normal operation, reversal, & obstacle detection conditions. Also included will hebe variations on temperature & grade. There can be more than 30 load cases contained in the load matrix. Some of the loading loadinconditions may be conflict with respect to others. It is the responsibility of the analyst to evaluate each loading condition using FE s FEAjudgment.The work highlights the optimization of power liftgate subsystem for weight reduction. The optimized sub-system not only met the subperformance requirements for the power loadcase It also ensured that mass is below the baseline mass of the liftgate. A worst loadcase.power load case is considered for the optimizations using technique available in HyperWorks® OptiStruct. There is approximately e OptiS1.5 kg of weight reduction compared to baseline design.IntroductionThe liftgate subsystem that is used for the study is a typical system with a power liftgate and a manual iftgateliftglass assembly. a. Power Liftgate Systems: Activation of the system completely opens the liftgate Systems until it comes to a stop. Reactivation of the system closes the liftgate in the latched position. b. Manual Liftglass Assembly: The Liftglass is Unlatched, pulled open, allowed to , auto-rise, and then slammed to close. rise,The liftgate subsystem in an SUV is typically manual. In this vehicle, power liftgate has been madeoptional. Same subsystem assembl is used for both manual and power liftgate variants. The liftgate ame assemblyshould meet the performance targets for both cases and should not be over designed for manual system. shouldThe loading is a combination of gas strut and actuator loads, in which a load matrix is developed specificto each vehicle & type of power system used. The matrix will include combinations of normal operation,reversal, & obstacle detection conditions. Variations on temperature & grade are included. There can be acle Vmore than 30 load cases contained in the load matrix. Some loading conditions may be in conflict withrespect to others. The worst load case is considered for further study. The grade (also called slope, considerincline, gradient, pitch or rise) refers to the amount of inclination of the road surface to the horizontal. This )grade is included in the gravity card. 1Simulation Driven Innovation
  2. 2. This work highlights the optimization of the liftgate subsystem to meet the performance targets as well asmass reduction of the power liftgate. Inner panel, reinforcements and plates (figure1a) are considered as figure1a)design variables. Displacement and stresses are considered as design constraints. The existing liftgate is acementof Aluminum and satisfies most of the static and dynamic performance targets of the manual liftgate. In targetorder to satisfy the performance target of the power liftgate (where the loading magnitude is 3 times ®higher than that in the manual case) the optimization techniques available in HyperWorks OptiStruct techniquewere used to get the effective thickness for reinforcements and plates to meet the required criterion ctivewithout increasing the weight of the existing design.Analysis PhaseGeometry and FE ModelA OptiStruct finite element (FE) model was employed ,which consists of fully trimmed liftgate with inner tructpanel, outer panel, strut bracket, strut plates, hinge reinforcements ,hinge assembly, glass assembly, hinge assemblyliftgate interface components such as latch–striker assembly, contact wedge and slam bumpers latch striker(figure 1a) and liftglass interface components such as latch–striker assembly, contact and slam bumpers. latch striker bumpersOuter and inner panels are connected with adhesive. Hemming is done along the edge of the outer andinner panels. Hinge reinforcement is connected with inner panel through spot welds. Hinge assembly isbolted to inner panel and hinge reinforcement. Hinge pivot is modeled in such a way that liftgate rotatesfreely about hinge axis. Glass hinge pivot is in-line with the liftgate hinge and the glass hinge is modeledin such a way that liftglass rotates freely about the common hinge axis. at Figure 1a: Liftgate assembly a: Figure 1b: Reinforcements and plates 2Simulation Driven Innovation
  3. 3. Process Flow:Steps for Topology and gauge optimization are shown in figure 2. Figure 2: Process flow chart for Analysis PhaseDefinition of Optimization Parameters:Topology and Gauge optimization technique is selected in order to get the optimal design and optimalthicknesses to meet the performance target and for significant weight reduction. In the topologyoptimization, design variable is inner panel thickness, which is defined by DESVAR card and related toPSHELL properties. The objective function of the present work is to minimize the volume of inner panelwhich can be defined by DESOBJ card. Deflections and volume responses is created through response responsescard. Ball stud deflection is design constraints which can be defined by DCONSTR card. Thickness of theinner panel is varied from 10 mm to base thickness. Base thickness is taken as the thickness of themanual liftgate. Problem definition for topology optimization is described in the table 1. 1For gauge optimization, thickness of reinforcement and plates is the design variable which is defined byDESVAR card and is related to individual PSHELL properties can be defined by design variable propertyrelationship card. The objective function of the present work is to minimize the weight of reinforcementsand plates which can be defined by DESOBJ card. Deflections and stress responses are created throughresponse card. Displacement and stress are the design constraints which can be defined by DCONSTR mentcard. Thickness of the reinforcement and plates is varied from base thickness of 2 mm and 3 mmrespectively. Base thickness is taken from the manual liftgate. Problem definition for gauge optimization isdescribed in the table 2 for each load case. 3Simulation Driven Innovation
  4. 4. Design Objective Design Gage Responses Variables Range Constraints Function 10 mm to Minimize Power Inner panel Displacement Displacement Base the Loading Thickness and Volume < 1mm Thickness volume Table 1: Problem defination for Topology optimization Design Objective Design Gage Responses Variables Range Constraints Function Base Displacement Power Reinforcements Displacement Minimize Thickness < 1mm Loading and Plates and Volume Volume to 2mm Stress < YS Combined Base Displacement (Power Reinforcements Displacement Minimize Thickness < 1mm load + and Plates and Volume Volume to 3mm Stress < YS Gravity ) Table 2: Problem defination for Gauge optimizationResults & Discussions:Topology and gauge optimization is performed separately on Inner panel and reinforcement, platesrespectively. This is done because increasing thickness favors gravity loading, so no significant reductionin ball stud displacement. This study tells which area on the inner panel need to be stiffened. Figure3 areas eedshows the inner panel mass distribution and critical area that need to be improved. Based on this studythe changes are done on the reinforcement that is merging the 2 reinforcement into one shown in figure4which meets the performance targets on power liftgate. For mass reduction the scope was to performfurther gauge optimization on the reinforcement and the hinge and strut plates. The optimized thickness isshown in the table 3. Hence gauge optimization for power load and combined load (powerload + Gravity)conditions is performed and effective thickness values are obtained. There is almost 1.5 kgs of weight oreduction in the reinforcement and plates without deviating from both the manual and power liftagateperformance. 4Simulation Driven Innovation
  5. 5. Figure 3: Mass Distribution and area need to be stiffen Figure4: Changes done on reinforcements Current Base Components Optimized Design Gauge Reinforcement 3.0 mm 2.1 mm Plates 4.5 mm 3.5 mm Table 3: Thickness comparsion for base design and current optimized designConclusions & Remarks:Using topology optimization technique on inner panel, it was possible to increase stiffness to meet theperformance targets of power liftgate without affecting the performance of the manual liftgate.Using this technique one component is eliminated from the total assembly, by which the manufacturing y,cost is saved.Using gauge optimization technique, approximately 1.5 kgs of weight is reduced in the liftgate withoutdeviating from both the Manual liftgate and power liftgate performance. ACKNOWLEDGEMENTSThe author would like to thank Mr. Elliot Deavasagayam (EGM - Body & Exterior Engineering, GMTCI),Mr. Edward J Sizen (Director - Vehicle Systems) and Dr. Rao M Chalasani (GM India Director, DirectorGM India Advanced Vehicle Development), for giving us the opportunity to work on this challengingproject and to present this paper in Altair user conference. We would like to thank our colleagues for theirvaluable support. REFERENCES[1] HyperStudy 10.0 Manual. 5Simulation Driven Innovation