3Suspension PurposeIsolate passengers and cargo from vibration and shockImprove mobilityImprove vehicle control
4Basic Terminology Sprung Mass Mass of all components that do not move much when suspension is displaced. (given the frame as a fixed reference)(Frame, engine, passengers, etc,)Some suspension components are actually partially sprung mass
5Basic Terminology Unsprung Mass Mass of components that move when suspension is displacedMinimizing the unsprung mass allows for more optimal suspension operation
6Basic TerminologyBumpVertical displacement of entire sprung mass
7Basic Terminology Roll Front View angular rotation of the sprung vehicle mass
8Basic Terminology Pitch Side View angular rotation of the sprung vehicle mass
9Basic Terminology Roll Center Center at which the sprung mass pivots about during a roll situation (lateral acceleration)This is a dynamic point: moves around throughout suspension travel
10Basic Terminology Pitch Center Center at which the sprung mass pivots about during a Pitch situation (fore/aft acceleration)This is a dynamic point: moves around throughout suspension travel
11Basic Terminology Camber Front View tilt of the tire. Leaning the top of the tire inboard adds negative camber
12Basic Terminology Toe Top view angle of the tire in a static situation Turning the front of the tire in is referred to as adding “toe in”Important for both front and rear tires
13Basic Terminology Steering Axis Axis about which the wheel/Tire rotate about during steering inputsAlso known as “King Pin Axis”
14Basic Terminology Caster Angle Side view tilt of the steering axis. Creates camber change with steering inputCreates a restoring force for centering steering wheel
15Basic Terminology Caster Trail Side view distance from the steering axis ground plain intersection and the contact patch center pointCreates a restoring force for centering steering wheel
16Basic Terminology Scrub Radius Distance From which the ground plain intersection of the Steering axis and the center of the tire contact patchLarge effect on drivers feel and steering effort
17Basic Terminology Steering Arm Line between the steering axis and there steering linkage “tie rod”
18Basic Terminology Bump Travel Vertical distance wheel is able to move up from static position, with reference to vehicles sprung massDroop TravelVertical distance wheel is able to move down from static position with reference to vehicles sprung mass
19Passenger ComfortThe perception of vehicle comfort is very subjective. Much depends on the cabin conditions. The main objective of the designer is to minimize the rate of change of acceleration (jerk).
20Trophy truck video Front Independent double wishbone Suspension Rear Solid axleHigh horse power vehicle
32Advantages Fewer Individual Components Easier to cheaply manufacture and assembleSimplified drivetrain layoutHigh Load CapacityAxle Components are protectedCan use leaf or coil springsAlso can accept many different types of linkages to gain desired geometrySolid wheel attachmentMinimal alignment eminence
33Disadvantages Disadvantages: Higher Unsprung Weight Can lead to “wheel hop”Axle wrap when in a leaf spring configurationHigh Roll Center HeightNot an Independent DesignCorners are coupledFixed Camber Angles
34Camber ChangeThe diagram below shows how the camber is statically fixed, and does not change in reboundThe middle diagram shows how the camber of the two wheels are linked to one another
35Solid axle adjustability As far as the static characteristics of the suspension the camber and castor are preset in the manufacturing of the axle housingHowever the dynamic characteristics of the suspension are highly adjustable with various forms or bar linkagesThere are many different linkage designs for a solid axle ranging from leaf springs to multi-link suspension systems
37Double Wishbone Suspension With Unequal Length Upper and Lower ArmsFound On:-Stock Cars (Front)-Corvettes (C5 &C6) (Front and Rear)-Honda Civics (‘88-’00) (Front)-Most Modern Sports Cars
38Advantages Arguably the best handling suspension design Wheel gains negative camber in bumpLow Unsprung WeightPackaging does not compromise stylingLow HeightMany different geometry characteristics possibleDesigner can design suspension with minimal compromisesInfinite adjustability, with the most easeVehicles roll centers can be placed almost anywhere
39Disadvantages More expensive More components to make and assemble Alignment and fitment are critical to vehicle performance, large area of adjustmentTolerance of parts must be smallerRequires constant alignment checks for optimum performanceMore complexDesign often becomes more complex because all suspension parameters are variableFrame has to be able to pick up a-arm inboard pointsTire scrub occurs with vertical wheel displacementHowever this can be minimized during design
40Double Wishbone Tuning The double wishbones complexity enables it to be adjusted quite readilyThe suspension geometry can be adjusted in two distinct waysMove the location of the inner Chassis attachment pointsAdjust the inclination of the upright and the pick-up locations on the uprightThe camber, castor, roll center, etc…. can all be individually adjusted on this type of suspension relatively easily.
42Suspension Types: MacPherson Strut Invented by Earl S. MacPhersonFirst used on the 1951 Ford ConsulFord held the patent for the Macpherson strut system by many rival companies invented similar systems to avoid Ford royalties
43Suspension Types: MacPherson Strut AdvantagesLow production costsStamped constructionPreassembledStrut body carries spring assemblyCompactSimple mounting and no need for an upper control armSimplicityReduction in fasteners and alignment of vehicle suspension components.
44Suspension Types: McPherson Strut DisadvantagesLarge camber variationBody roll and wheel movement contribute to camber attitudeVertically tall mounting positionThis compromises vehicle stylingRough rideSome ride comfort may be lost, as it is hard to move smoothly because of bending input forceDangerous replacementThe spring must be compressed and assembled on the strut body, this causes the handling of a charged spring.
45Associated forces in the strut Since the strut serves as the upper control arm as well as the damper it is required to provide the force to hold the wheel at the desired camber attitude.
46Adjustment of MacPherson Strut Since the strut governs the King pin axis as well as the camber of the tire, these two parameters are linkedThe adjustability of the MacPherson strut is limited, due to its simplicityMost adjustability of the suspension is achieved by modifying the location of the upper strut mounting location.
47Suspension Types: MacPherson Strut MacPherson Struts are widely used on a variety of cars today from the everyday road car to world class race cars