Selection, Modification and Analysis of Suspension ... - IRD India

Selection, Modification and Analysis of SuspensionSystem for an All-Terrain VehicleEshaan Ayyar, Isaac de Souza, Aditya Pravin, Sanket Tambe, Aqleem Siddiqui & Nitin GuravE-mail : eshaan004@gmail.com, isaacd68@gmx.com, adityaraman91@gmail.com, sank_200956@yahoo.comAbstract - The real pleasure of driving for an off-roadenthusiast can be described as the thrill of the terraincoupled with a capable machine to handle the terrain.However, this pleasure can be derived only when thecomfort level of the driver is maintained. Thus, it isconcluded that the suspension system (which is responsiblefor providing a comfortable ride quality to the driver) isone of the most important sub-systems to be designed. Thispaper aims at selecting, modifying, analyzing andfabricating a suspension system capable of handling roughterrains while maintaining the ride quality.I. INTRODUCTIONSuspension system is the term given to the systemof springs, shock absorbers and linkages that connect avehicle to its wheels.When a tire hits an obstruction,there is a reaction force and the suspension system triesto reduce this force. The size of this reaction forcedepends on the unsprung mass at each wheel assembly.In general, the larger the ratio of sprung weight tounsprung weight, the less the body and vehicleoccupants are affected by bumps, dips, and other surfaceimperfections such as small bridges. A large sprungweight to unsprung weight ratio can also impact vehiclecontrol.The main role of suspension system is as follows:It supports the weight of the vehicleProvides a smoother ride for the passengersProtects the vehicle from damageKeeps the wheels firmly pressed to the ground forbetter tractionIt isolates the vehicle from road shocksThere are three basic components in any suspensionsystem:SpringsDampersAnti-sway barsThe following types of suspension systems aregenerally available in the market:1. Mechanical Suspension System:i) Independent SuspensionLeaf Spring SuspensionMacPherson SuspensionWishbone Suspensionii) Dependent SuspensionRigid Axle Suspension2. Electric Suspension System3. Magnetic Suspension SystemII.SELECTION OF SUITABLE SUSPENSIONSYSTEMThe selection of the suspension system which willbest satisfy the requirements of an ATV was carried out.Out of the many available suspension systems in themarket, the Double Wishbone Suspension System wasselected for the ATV. This selection was done based onthe following basic parameters:1. Load bearing capacity2. Flexibility3. Cost4. Technical aspects: Camber, Stiffness, Rolling5. Availability of parts and componentsIII. DESIGNThe design procedure for the chosen suspensionsystem is divided into two stages:1. Primary design:Basic design and development of SuspensionSystem components62ISSN : 2319 – 3182, Volume-2, Issue-4, 2013

International Journal on Theoretical and Applied Research in Mechanical Engineering (IJTARME) Modified design parameters based onapproximation of Dynamic ConditionsStatic testing and analysis2. Secondary design:Mathematical modeling of finalized concept ATVDynamic testing and analysisModification of Design Parameters based onDynamic Testing resultsThe following components are to be designed:Suspension SpringWishbonesKnuckleDesign procedure for the components of Suspensionsystem is dependent on the suspension geometry (asshown in Fig.1 and Fig.2); found out by taking intoconsiderations the design constraints. According to the mass distribution of 60:40 (Rear:Front)Mass per wheel (Front) = 50 kgMass per wheel (Rear) = 80 kg1) Front springAngle of inclination of the strut = 60 (from horizontal)Point of attachment of strut = 10” (254 cm) from chassisend ….(from suspension geometry)Reaction force acting from the ground on the wheel =(Mass per wheel * 9.81) N= (50 kg * 9.81) N= 490.5 NFig.1 Front suspension geometryFig.2 Rear suspension geometryDesign of suspension springAssumptions made: Sprung mass = 260 kg(approx.) Factor for static to dynamic conditions : 2.5Fig.3. Forces on front wishboneConsidering the wishbone hinges as the point aboutwhich moment is taken;Horizontal distance of reaction force from hinge point= 17.36” (44.09 cm) ….from suspensiongeometryHorizontal distance of strut attachment point from hingepoint = 8.2” (20.828 cm)By taking moment about hinge points :490.5 * 17.36 = Spring Force * 8.23 Spring Force = 1034.6 NConsidering the dynamic factor,Dynamic force acting on the spring = 2586.59 NAccording to the ride conditions and road quality for anATV, it is concluded that the optimum spring travelshould be approx. 4” (10.16 cm)Hence, Required Spring StiffnessDynamic Spring Force=Spring Deflection= 25.46 N /mm=2586 .59101.663ISSN : 2319 – 3182, Volume-2, Issue-4, 2013

International Journal on Theoretical and Applied Research in Mechanical Engineering (IJTARME)25 N/mm2) Rear springAngle of inclination of the strut = 80 o (from horizontal)Point of attachment of strut = 6.5” (16.51 cm) fromchassis end…(from suspension geometry)Reaction force acting from the ground on the wheel= (Mass per wheel * 9.81) N= (80 kg * 9.81) NFig.4. Forces on rear wishboneConsidering the wishbone hinges as the point aboutwhich moment is taken;Horizontal distance of reaction force from hinge point =14” (35.56 cm) …..(from suspension geometry)Horizontal distance of strut attachment point from hingepoint = 6.38” (16.02 cm)By taking moment about hinge points :784.8 * 14 = Spring Force * 6.38 Spring Force = 1722.13 NConsidering the dynamic factor,Dynamic force acting on the spring = 4305.325 NAccording to the ride conditions and road quality for anATV, it is concluded that the optimum spring travelshould be approx. 4” (10.16 cm)Hence, Required Spring Stiffness= =Table 1. Spring dimensionsSr.No.ParameterFrontSuspensionRearSuspensionMaterial Grade 4 oil hardened spring steel1 Wire diameter 11 mm 11 mm2 Inner coil 55 mm 55 mmdiameter3 Outer coil 66 mm 66 mmdiameter4 Total number 22 14of turns5 Free length of 365 mm 292 mmstrut6 Pitch of 18 mm 27 mmsuspensionspring7 Eye-to-eye 456 mm 484 mmlength of strut(unloaded)8 Stiffness 25 N/mm 40 N/mm9 Maximumdynamic springtravelB. Design of wishbones101.12 mm 100.88 mmThe design parameters that govern the dimensions of thewishbone are :i) Available length for wishbones: 32 inchesii) Available width for wishbones: 20 inches1) Front wishboneThe front wishbones are standard A-arms and thedimensions are decided on the basis of the length andwidth constrains (as shown in Fig.5). The wishboneshave unequal length.The upper wishbone is shorter thanthe lower wishbone.The advantage of having differentlengths is that when the car takes a turn a negativecamber is induced which increases the stability.Theunequal lengths also result in a positive camber of1.5⁰.The strut is mounted on the lower wishbone and theknuckle is attched to the wishbone by a ball joint. Thewishbone is then tested using Autodesk Inventor.40 N/mm= 42.375 N64ISSN : 2319 – 3182, Volume-2, Issue-4, 2013

International Journal on Theoretical and Applied Research in Mechanical Engineering (IJTARME)2) Rear wishboneFig.5.Front WishboneInitially, the A-arm was considered for the rearsuspension. However, while the vehicle takes a turn, dueto the horizontal forces acting on the attachments of thewishbones and the knuckle and due to lack of steeringon the rear wheels, there may be toe-in or toe-out of thewheels. This may lead to improper steering and mayresult in unbalance. Excess toe-in may cause oversteerwhile turning leading to loss of control. Excess toe-outmay cause understeering while turning.To avoid anytoeing, the A-arm is converted into H-arm (as shown inFig.6). Thus the vertical pin knuckle-wishboneattachment is converted into horizontal pin attachment.This prevents formation of an axis and hence thepossibility of toeing of the wheels. This ensures properalignment and steering. It also increases the ride stabilityand linear travel.Fig.7.Front KnuckleDue to lack of funds the above design could not bemanufactured.The knuckle of a maruti 800 wasmodified so that it could accmmodate the designedwishbones.The modified design is shown below.Fig.8.Modified Front Knuckle2) Rear knuckleThe rear knuckle was designed to accommodate thedesigned H-arms (Fig.9)C. Design of knuckleFig.6.Rear WishboneA knuckle is used to connect the wishbones to thewheel hub.1) Front knuckleThe first step in the design was market research. Astandard knuckle of MARUTI SUZUKI ESTEEM wasselected from the market and studied. The suspensionsystem of the Esteem is MacPherson type, hence theknuckle had to be modified. The designed knuckle isshown. (Fig.7)Fig.9.Rear Knuckle65ISSN : 2319 – 3182, Volume-2, Issue-4, 2013

International Journal on Theoretical and Applied Research in Mechanical Engineering (IJTARME)The rear knuckle too could not be manufactured due tolack of funds.the knuckle of an esteem was modified asshown in the figureThe rear upper wishbone was tested as the strutattachment point was on the upper wishbone. The hingeswere considered as fixed points and a load of 4305.325N was applied at the strut attachment point.Fig.10.Modified Rear KnuckleTESTING OF DESIGNED COMPONENTSAnalysis of all the parts was done using Autodeskinventor.WishbonesThe front lower wishbone was tested as the strut isattached on the lower wishbone due to which most ofthe load acts on the lower wishbone. The wishbone wastested on Autodesk inventor. The two hinge points andball joint were considered as fixed points and a load of2586.59 N(load on spring) was applied at the strutattchment point.Load applied: 4305.325 NFactor of safety: 1.5Result: Design is safeB. KnucklesFig.12.Rear WishboneThe hub end of the knuckle was considered fixedand a load of 2586.95 N was applied at the lower part ofthe knuckle as shown in fig.13.Fig.11.Front WishboneLoad applied: 2586.59 NFactor of safety: 1.5Result: Design is safeLoad applied: 2586.59 NFactor of safety = 3.5Result: Design is safeFig.13.Testing of front knuckleThe attchment for the front knuckle was tested and theresult (Fig 14).66ISSN : 2319 – 3182, Volume-2, Issue-4, 2013

International Journal on Theoretical and Applied Research in Mechanical Engineering (IJTARME)Load applied: 2586.59 NFactor of safety = 3.5Result: Design is safeFig.14.Testing of front knuckle attchmentThe rear knuckle was tested in a similar way.theresults are shown belowIV. FABRICATIONThe fabrication of all the parts was done in theworkshop.The final fabricated parts are shown below.Material used for wishbones: AISI 1026Dimensions of pipe: 19 mm ID, 3 mm thicknessMaterial used for all other fabrications andmodifications:Mild Steel plates of thickness 4 mm and 8 mmLoad applied: 4305.325 NFig.15.Testing of rear knuckleResult: Design is safe (Factor of safety = 4)Fig.17.Fabricated front wishboneFig.16 Testing of modified rear knuckleFig.18.Fabricated rear wishbone67ISSN : 2319 – 3182, Volume-2, Issue-4, 2013

International Journal on Theoretical and Applied Research in Mechanical Engineering (IJTARME)Fig.19 Front knuckle with attachmentV. REFERENCES[1] Christina Elena Popa, ‘Steering System andSuspension System’, University Of SouthQueensland[2 ] Edmund F. Gaffney and Anthony R. Salinas,‘Introduction to Formula SAE Suspension’,University Of Missouri[3] Mitchell W., ‘Force based roll centres andkinematic roll centres’, SAE-India[4] Gertz L., L. Laranja, ‘An off-road suspensionsystem’, University Of Brazil[5] Gerrard M., ‘Roll centres and jacking forces’,Engineering Solutions[6] NK Giri, ‘Automobile Mechanics’, KhannaPublications, 1996[7] Kirpal Singh, ‘Automobile Engineering’,Standard Publishers Distributors, 2008[8] Thomas D.Gillespie, ‘Fundamentals of VehicleDynamics’[9] T.K. Garrett, K. Newton, W. Steeds, ‘The MotorVehicle’, Butterworth-Heinemann, 2000[10] Design Data Book, PSG Technology InstituteFig.20 Rear SuspensionFig 20. Final Assembly68ISSN : 2319 – 3182, Volume-2, Issue-4, 2013