fsae suspension

7/16/2019 FSAE Suspension

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Final Presentation to Engineering Panel

Seth Beckley, Kevin Gygrynuk, Josh Hilferty, Mike Teri



FSAE “The Formula SAE ® Series competitions challenge

teams of university undergraduate and graduatestudents to conceive, design, fabricate and compete

with small, formula style, autocross racing cars……Over the course of three days, the cars are judged in aseries of static and dynamic events including:technical inspection, cost, presentation, andengineering design, solo performance trials, and highperformance track endurance.”1

1 http://students.sae.org/competitions/formulaseries/west/eventguide.pdf



Sponsor Mike Hawley

Employed by W. L. Gore

Former UD FSAE member, designed the suspensionsystem for two consecutive years

Resource of much valuable information on suspension



Suspension: How it Works Key Parts:

upright

lower a-arm

upper a-arm

Spindle/

rotor red = points fixed

to chassis



Key Parts Continued

pushrod

rocker

(bell crank)shock

red = points fixed

to chassis



Key Parts: Sway Bars and Tie Rod

Sway Bar

sway bar arm

and linkage to

rocker

tie rod to

Steering rack



Suspension: How it WorksKey Terms:

Camber: The angle of the wheel with respect to vertical.

Kingpin Angle: The angle measured between the steering axis and vertical.

Scrub Radius: The distance between the steering axis and the wheel’s contact patch.

Image taken from: www.mgf.ultimatemg.com/



Suspension: How it works Roll Center:

Defined by intersection of lines between the tire contactpatch and instant centers of wheel travel.

Defines the instantaneous point about which thechassis rolls



Key Terms: Anti-Dive: A suspension geometry setup that resists the diving action of the nose of the

car from diving during braking Anti-Squat: A suspension geometry setup that resists the diving action of the tail of the

car from diving during acceleration

Center of Gravity

A-arms

The closer the convergence points are to the height of the center of gravity, the more anti-

dive or anti-squat characteristic is present

Image taken from Competition Car Suspension, Allan Staniforth

Suspension: How it Works



Project Scope Determination of most efficient suspension configuration and

geometry Determination of spring and damper requirements Determination of anti-dive/anti-squat requirements

Determination of optimal values for camber, caster, and kingpin anglesas well as scrub radius

Determination of attachment points at wheel, brake, steering rack,axle, and chassis interfaces

Design based off of existing wheels and tires Design synthesis and real-time simulation of complete and functional

suspension system Output a working, useable suspension system for the 2010-2011 UD

FSAE car Maintain a high level of easy adjustability for further tuning of the

suspension system



FSAE Rules Applicable to

Suspension Minimum wheelbase of 60”

If front and rear track are of different lengths, smaller

track must be at least 75% of larger track

Minimum of 2” useable wheel travel

Minimum of 1” jounce

Minimum of 1” rebound



Additional Constraints Budget of $1000

Constraints imposed by other teams Drivetrain – axles and rear hubs

Driver controls - steering rack location

Chassis – construction of chassis

Cooperative – brake rotor and caliper selection



Metrics and Target Values Wheelbase: 61” Front Track: 50” Rear Track: 2” less than front Adjustable Anti-Dive and Anti-Dive: 1” vertically on specific pickup points

Roll Center: Stable, < 1” vertical movement over 1.5” deflection in roll, < 1’horizontal movement Scrub Radius: < 1” Camber: -2⁰ static camber, maintained over ¾” deflection in roll Kingpin Angle: 0-5⁰ Caster Angle: 0-5⁰

# Tools to Adjust and Tune Suspension: 3 tools Adjustments easy to access: Yes Camber and toe adjustment without disconnection of parts: Yes Material Strength: Factor of safety for range of normal operation: > 2 Material Machinability: Maximize Material Weight: Minimize



Suspension Style Choice Unequal A-arms

Most commonly used for racing suspension, almostexclusively used in FSAE

Style most suited for stiff racing independentsuspension

Reliable, with predictable and calculable motions andforces throughout travel.



A-arm Length Adjustability Threaded Chassis Mount

Typical and reliable method, maximize strength and rigidity

Threaded A-arm

mounts to chassisspherical rod end

To adjust, bolt is removed,

Locknut loosened, and

rod end turned

Locknut



Camber Adjustability Shims at upright Particular shim thicknesses

can be correlated tospecific camber changes

Easily adjustable: loosen bolts

and drop shim into place

Reliable and successful concept,

upright a-arm clevis

shim



Anti-Squat and Anti-Dive Adjustability

Anti-Squat and Anti-Dive Adjustability

Adjustment is achieved by switching out different sets of bushings.

Bushings are cheap and easy to manufacture.

bushing

bushing



Kinematic Design Extensive use was made of

Excel spreadsheets anddynamic CAD models tosimulate suspension andachieve desired performance

characteristics. Two Dimensional Simulation

of Suspension in Roll

-20

-15

-10

-5

0

5

10

15

20

25

30

-30 -25 -20 -15 -10 -5 0 5 10 15 20 25 30

Y

( i n

)

X (in)

Body Roll Simulation

Neutral

1.5" Deflection Right Roll

1.5" Deflection Left Roll



Lower A-arms Dimensions determined by kinematic and force

analyses.

Design based on vehicle dynamicstheory and researchof previously successful designs.



Upper A-arms Dimensions determined by kinematic and force

analyses.

Design based on vehicle dynamicstheory and researchof previously successful designs.



Push Rod Design Transfers bump force to shocks

Supports weight of car in neutral stance



Rocker Design Determines ratio of pushrod motion to spring

compression.

Linkage point for sway bar



Sway Bar Design Individual project

assigned toSeth Beckley

Typical FSAE designstyle

Stiffness adjustability

achieved by changinglever arm length



Force Analysis The force analysis on the final design centered around

maximum cornering and braking forces estimatedduring competition.

The team decided upon a goal of structural integrity through a 5g vertical impact.

The estimated braking and turning values were

conservative, and surpassed the benchmarked 1.4 gexpected in competition.

The rockers were designed to optimize the travel of theshock absorbers.



Force Analysis Factor of Safety

The factor of safety for the suspension components undernormal turning and breaking is over 5.

Failure of Components The rod ends are the weakest members of the suspension

structure, and have an estimated failure rating of 4500 lbf . Rod ends are expensive and not as easy to replace as other

hardware so the mounting bolts have been undersized toprovide a factor of safety less than the components

themselves. Finite Element Analysis

A finite element analysis was conducted using solid modelingtools as well as manual calculations to ensure eachcomponent’s performance



Ride and Roll Rates Using vehicle dynamics theory, shock travel limits, and

bump and cornering conditions, desired ride and roll rates were determined:

Ride Rate:

Front: 148.4 lb/in

Rear: 146 lb/in

Roll Rate: Front: 18750 lb•ft/rad total, 15483 lb•ft/rad contributed by

springs, 3267 lb•ft/rad contributed by sway bars

Rear: 20875 lb•ft/rad total, 14016 lb•ft/rad contributed by springs, 6859 lb•ft/rad contributed by sway bars



Spring Stiffness and Damping Spring Stiffness was determined by desired ride and

roll rate, and the ratio between pushrod movementand spring compression.

Damping can be guessed at, but not dialed in until caris driven and tested.

From spring stiffness calculations, the target

suspension frequency was estimated to be 3 – 3.5 Hz which can be achieved through shock adjustability.



Final Product To determine the achievement of the geometric target

values the suspension was assembled onto the partially completed frame and measured.

Assembly will continue throughout the final week of Phase 4.

The final assembly of the suspension will then be

presented to the sponsor on December 17th

2010.



Performance Evaluation/Validation Chromoly tubing and welded connections will be tested to

failure and compared to force analysis during the final week of the Fall 2010 semester.

The car will not be completed until the very end of seniordesign, and thus testing of the effectiveness of the system

will have to be postponed until winter session.

A test plan has been developed to analyze the performance

under driving conditions. Once the car is built, the UD FSAE club will take over

testing and tuning of the suspension using methodsoutlined by Team Suspension



Performance Evaluation Measures Camber Effectiveness: Tire temperature analysis

after test runs

Load Transfer: G force measurements from onboarddata acquisition

Jounce, Body Roll & Anti Squat/Anti-Dive: onboardmeasurement and tuning

All evaluated performance measurements can beadjusted through adjustability in the suspension and will be tuned to optimal properties.



Camber Effectiveness The efficiency of the camber, ride, and roll rates can be

measured by analyzing tire temperature distributionafter 5-10 laps around the track.

Each tire’s temperature will be measured at threelocations on the tire 1” from the outside shoulder

1” from the inside shoulder

Center of the tire Possible results of the tests and their solutions have

been outlined in the test plans given to the UD FSAEclub.



Load Transfer G-force analysis will be completed through the car’s

onboard computer.

Acceleration measurements will be recorded at every point along the line the car travels around the track.

The data extracted from the computer will enable theteam to calculate resultant G-forces.



Jounce, Body Roll & Anti Squat/Anti-Dive

These performance targets will be evaluated by directly measuring them as the car is put throughtesting on the track.

Under maximum braking, accelerating, and corneringconditions, these properties will be measured.

From this analysis the car will be finely tuned to

achieve the set target values.



Budget Materials Cost = $322

Aluminum, Steel, Chromoly Tubing

Parts Cost = $550 Bearings, Rod Ends, Spherical Joints, hardware

Miscellaneous Costs = $100

Manufacturing Cost = ~$0.00

All fabricating was done by team in FSAE shop andstudent shop at no charge

Total Cost = $972



Project Management The design of each component in the suspension

assembly have been completed and optimized.

All geometrical target values have been met.

The suspension will be tuned after testing iscompleted in order to satisfy performance metrics.

Budget has been reduced and falls within the

constraint. Team is on schedule to finish project and present

results to the sponsor on December 17th 2010.



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