Suspension Design Procedure

Suspension Design ProcedureThe following is the algorithm for suspension designing to be followed in given order I Decide type of suspension system IIDecide best possible set of tires and wheelsIII Estimate basic dimensions wheelbase,trackwidth(s), cog height I !et static values for suspension parameters" #odel the geometry to ensureminimum plausible change inparameters IDesignandvalidatesuspensioncomponentsTYPE$e take Double wishbone here"%owever you need to choose yoursTIRE & WHEEL SELECTION !ometimes you are bound by competition rules to use a particular set of tires&wheels%owever, if not then you need to decide the optimum set of tires and wheels'ne method to do this is using the wheel decision matri(Ref to research paper illustrating decision matrixASSUMPTIONS AND ESTIMATES$heel base is defined as the distance between the front and rear a(le centerlines") longer wheelbase provides a greater straight line stability, whereas a shorter wheelbase ensures better maneuverability"Longitudinal load transfer is inversely proportional to the wheelbase.*ront and rear track width are assumed, it is an important factor that resists overturning"Lateral load transfer is inversely proportional to trackwidth.The ma(imum height of the center of gravity of the cariscalculated,assumingthatthecarpasses thetilttest,whichinvolvestiltingthecaratan angle of +,- on a platform"The total weight of the car, weight distribution and valuesofsprungandunsprungmassare calculated"Design .arametersThefollowingparametersaretobekeptinmind while beginning suspension design/0aster0amberToe1ingpin Inclination#otion 2atio2oll center height3ump steerShark Model Camber/4egativecamberisusedinstaticconditionsso thatduringroll,whenthetiretiltsoutwardsthetire contactpatchisma(imi5edprovidinggreaterlateral force and thus a better grip" Caster/.ositive0astergeneratesnegativecamberonthe outsidetirewhenthewheelissteeredandpositive camber on the outside tire" During cornering to maintain a suitable tire contact patch a slight negative camber is re6uired and hence a positive caster is used"Toe/Toe7inresultsinincreasedstraight7linestability,while toe7out6uickensthetransitionalbehavior"Toeonthe front tires is not a ma8or contributing factor, but the rear tiresaregenerallyincorporatedwithatoe7insoasto reducetheirtendencytogolooseduringcorneringand hence maintain the rear stability"Kingpininclination:Itistheanglemadeby thesteeringaxiswiththeverticalinfrontor rear view. The prime motive of providing a king-pin inclination is to reduce the scrub radius i.e. theking-pino!setatground.Scrubradiusis re"uiredtobeminimi#edtoreducesteering e!ort.Motionratio/Itisdefinedastheratioofwheel travel/springtravel"9enerallyarisingrateis preferred for increasing stiffness with travel"RollCenter/Thepointofintersectionoftheroll a(iswiththeverticalplanethroughthewheel centres is called the roll centre" The roll center height is kept low to avoid :8acking;, i"e",lifting of the inner rear wheel during cornering"KINEMATIC ANALYSIS2oll 0entre migration9raphs for various parameters$ront camber in bump%ear camber in bump$ront toe in bump%ear toe in bump$ront spring travel%ear spring travel2oll !imulation%ear camber in roll$ront camber in rollDesign and )nalysis )fter the suspension geometry was simulated and optimi5ed, the ')D T2)4!*E2$henevere(ternalforcesactonthe tires,transferofloadtakesplace dependinguponthedirectionand magnitudeofforces"Thisisbecause thecentreofgravityisabovethe groundandnetmomentshavetobe balanced at all points">)TE2)> >')D T2)4!*E2Duringcornering,loadtransfertakes placefromtheinsidepairofwheelsto theouterwheels"Thisistermedas lateral load transfer" Thus,theoutertiresaresub8ectedto ma(imum lateral force">)TE2)> >')D T2)4!*E2>'49IT?DI4)> >')D T2)4!*E2$hilebrakingoraccelerating,loadshifts fromthereartofront(braking)orvice versa (acceleration) due to inertia forces" Thisistermedaslongitudinalload transfer" Thus,thefronttiresaree(perience greaterbrakingforcewhilethereartires are loaded under acceleration">'49IT?DI4)> >')D T2)4!*E29E4E2)> )..2')0%Tofindforces,wefirstdetermine lateraland&orlongitudinalload transfer"$ethenselectthe wheel(s)whicharesub8ectedto ma(imumloadstofindlimiting forces" There are two primary conditions thatneedtobesatisfiedfor making steady turns&braking and acceleration/Thenetforcealonga particular direction must be 5ero"The net moments about any point must be 5ero" )llforcesoriginateatthetire contactpatches@beitbraking, corneringoracceleration"$ethen navigate upwards tobalance forces andmomentsandthusfindthe forcesactingonthedifferent suspensioncomponentslike uprights, a7arms and pushrods"0'24E2I49During cornering, lateral load transfer takes place from the inner to outer tires" %ence, it is sufficient to consider the forces on the outer tires only@ as these are sub8ected to greater forces"$estartbytakingcoordinatesfromthe front view of the suspension system (front)"4e(t,weassumeacriticalvalueof cornering acceleration (say D"Eg)>ateralloadtransferiscalculatedandis addedtohalfthestaticloadtogetthe vertical forces acting on the outer tire"Theloadontheoutertireismultipliedby thisfactor(D"Eg)togetthema(imum cornering force"?prights'nlytheupperandlowerball8oints areconsidered"Theforcesonthe ball8ointscanbedeterminedby solvingtwolineare6uations/oneto balancethecorneringforceandthe other to ensure 5ero turning moment in the front view"*'20E! '4 ?.2I9%T! (ie 3)>> F'I4T!)$ishbone and .ushrodInthiscase,theforcesactingalongthea7armsandpushrod(ietensionand compression) have to be determined")proceduresimilartotheoneusedfor uprights is used, e(cept that there are three linear e6uations/ *orces in y7directionertical forcesTurning moments$I!%3'4E *'20E!$e have used a push7rod as opposed to the pull7rod shown above3raking and )cceleration Duringbraking,longitudinalloadtransfer takesplacefromthereartofronttires" %ence,itissufficienttoconsidertheforces onthefronttiresonly@astheseare sub8ectedtogreaterforces"During acceleration, load is transferred onto the rear a(leandhenceonlytherearsuspension needs to be analy5ed"$e start by taking coordinates from the side view of the suspension system (front)"4e(t,weassumeacriticalvalueof braking&acceleration (say D"Eg& Dg)>ongitudinalloadtransferiscalculatedand isaddedtothestaticloadontheparticular a(le"ThisisdividedbyGtogetthe ma(imum load on a tire"The load on the this tire is multiplied by this factor(D"Eg)togetthevalueofma(imum force"Duringbraking&acceleration,theuprights arestressedtoagreate(tent"%ence, onlytheupperandlowerball8ointsare considered"Theforcesontheball8oints canbedeterminedbysolvingtwolinear e6uationsfromthepointcoordinatesin the side view/ one to balance the cornering force and@theothertoensure5eroturningmoment in the side view"32)1I49 )4D 0'24E2I49/Itispossibletohavesimultaneousbrakingand turning"%owever,thecorneringandbraking acceleration will not be at their ma(imum values" ) value of g can be considered for both cases"*orcesaredeterminedinthesamewayas discussedearlierbytakingcorneringandbraking separately@andthentheforcesduetothetwoare added vectorially to get the resultant force'ncema(imumforceshavebeen foundout,theycanbeusedto decidethethicknessofthea7arms,pushrodetcandthetype and6ualityofbearings(spherical, rod7ends etc) to be used"EA)#.>E(for a *ormula !)E car)WHEEL ASSEMLY)fterthefinali5ationofsuspension geometryandcompletionofforce calculations, we proceed to