Preliminary Design Report.docx

7/29/2019 Preliminary Design Report.docx

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Preliminary Design Report

arun Kathaesign Head

ushkar Sikkaeam Vice-Captain

BJECTIVE

he objective of this project is to design, simulate, analyse

d then fabricate a racing vehicle intended for sale to then professional weekend racing enthusiast.

he vehicle should be aerodynamically designed, economic,fe and single seat high performance vehicle. Ergonomicsd safety have been an integral part of our design strategyd anthropometric data has been used. Special focus will be

ut on human safety, the ease of mass production of thehicle. Almost all the vehicle subsystems will be designed

d fabricated by the team indigenously.he vehicle will be fabricated meticulously by the team,ing state-of-the-art facilities, comprehensively satisfyingth the design goals and manufacturing constraints.

NTRODUCTION

onsidering that the vehicle is meant for a non professionalcing enthusiast, the Supra SAE car has been designed andbricated considering the fact that the vehicle should bempletely safe for the driver in case of collisions from any

de and should be stable enough to avoid toppling in case ofeep cornering (something that can be expected duringrning at high speeds). It should also be aerodynamicallyrrect for better maneuverability and road adherence even ate highest achievable speed of the vehicle (80km/h).hereby, the over-all vehicle development methodology thatand that will be followed by our team is stated below:

1. Design Considerations2. Task Assignment3. PVC modeling of roll cage4. CAD Modeling (Data utilized from PVC modeling)5. Analysis of CAD Model6. Ergonomics analysis7. Revision of CAD Model after ergonomic analysis8. Simulation of component assemblies and sub-

assemblies before fabrication.9. Chassis Fabrication & Suspension Systems Assembly10.Steering & Braking Systems Assembly11.Engine and Transmission Mounting12.Final Integration, testing & optimization

ue importance has been given to the rules and regulations

escribed in the SUPRA SAE India 2012 rule book. The

hicle adheres to all the rules and regulations mentioned ine rule book.

he team members have utilized their engineering knowledgeto designing a vehicle that gives raw racing fun, is very

fe for the driver, gives due importance to ergonomics and issy to control and drive at the maximum speed of thehicle.

PVC MODELING

Every design has certain shortcomings which should be

rectified in order to arrive at the final optimized design thatcan be fabricated without any difficulty and fulfils all theobjectives of the design.The intended purpose is to extract the parameters whichwould form the basis of CAD modeling. PVC modelingserved as a low cost method of exposing glitches in ourdesign. The design was rectified and was madeergonomically suitable and safe for the driver

ROLL CAGE DESIGN

OBJECTIVE

An improved power to weight ratio was an importantparameter while designing vehicle and with the limited powerand engine limitation, the only means to improve this critical

parameter is to reduce the overall vehicle weight. Anotherchallenge during the designing of the vehicle wasmaintaining the overall safety of the driver, as reducing theoverall weight of the vehicle compromised with the safety ofthe driver, hence additional safety measures had to be takento improve the safety of the driver.The function of the space frame is to protect the driver and

support front and rear suspension systems, engine, steeringsystem and other systems/sub-systems in the vehicle. The

objective of the frame design was to satisfy these functionswhile meeting the SAE regulations with specialconsiderations given to safety of the occupants, ease of

manufacturing, cost, quality, weight, and aesthetics.Moreover care has been taken to ensure that there are

minimum welds on the frame pipes and maximum bendsensuring better strength and less cost of production of thevehicle. Chassis members have been utilized efficiently toreduce the constraints during fabrication.


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MATERIALSELECTION

he rules define the cage to be made with materialsuivalent to the following specification: Steel members withleast equal bending stiffness and bending strength to 1018

eel or ASTM A106 Grade B & Tube Grade having arcular cross section with a 31.75 mm (1.25 inch) OD and aall thickness varying from 2.5mm to 3 mm for differentembers.aterials that can be used for this type of tubing are 1018ild Steel and 4130 Chromoly Steel. The 4130 Chromolyd the 1018 mild steel has the same modulus of elasticity, soing it does not affect the weight or stiffness in membersth the same geometry. However the increase in Yieldrength affects the bending strength. As the bending strengthaffected not only by cross sectional moment of inertia of

e material but also by the radius, the 4130 allows the usagea larger diameter tube with a smaller wall thickness. Thisturn can allow a reduction of weight. However, 4130

hromoly Steel would increase the cost of fabrication as theaterial is not available in our vicinity. 1018 mild steel is

ailable at Punjab Tubes Limited, Ludhiana. The proximity

source will put a huge impact on the cost of the vehicle,aking it more economically feasible than using 4130hromoly Steel. The chassis will be manufactured using bendbe construction at a majority of places. Welding joints, bothmple and MIG will be made in the vehicle.

RGONOMICS

nthropometric data was considered for the 95th

percentileale driver. Data like full functional length of arm, leg etc,ight, buttock to knee length etc. were taken. Angles b/w

nees and legs, torso etc were taken while taking ergonomic

ating data into account. To be doubly sure of the designnstraints acc to the rule book and ergonomics data, we alsoed a 3D mannequin of a 6 feet human, 95th percentile male.annequins or Digital Human models/virtual models wereeated based on anthropometry of the drivers to be used for

sualization, simulations as well as to aid in modeling thecupant seat. Good human formula racing vehicle interfacesign ensures that the vehicle cockpit will ensure ease oferation like a conventional vehicle. Measurements are such

ken that when seated, the angle between the fore-arms and

per arms of the driver subdues an angle near 120 degrees,hile on the steering as this is the most comfortable position

r steering-human interface.

ROLLCAGE

Frame was designed and analyzed using Ansys, Catia &SolidWorks 2007 software. While designing, there are a fewimportant loading situations that should be analyzed. Theseinclude frontal impact, side impact, rear impactand rollover impact. Special focus was put on ergonomics ofthe drivers, keeping in mind the safety and comfort.

Design weight comes out to 452 Kg with approximationsafter considering a factor of safety (FOS) 1.3. Since the Yieldstrength of material used is 386.6 MPa and as per the analysisthe maximum stress that the frame could bear came out to be66.42 MPa. Therefore calculating the factor of safety as perthe stress: 386.6 MPa / 66.42 MPa = 5.8115

(FOS is greater than 5 as per the rule book)

Frame weight < 68kgMaterial: AISI 1018

Round tubes used

Max width of roll cage: 900mmMax length of the roll cage: 2616mmMax height of the roll cage: 1100 mm

DESIGNCONSIDERATIONS

Self Weight of Roll Cage: 68 Kg

Other weights on roll cage:

Engine: 80 KgTransmission: 30 Kg

Driver: 70 KgOther weights: 100 Kg

Total Weight: 348 Kg

Design Weight: 452 Kg

FEAANALYSISOFROLLCAGE

Front Impact

It was assumed that worst case collision would be seen whenthe vehicle runs into a stationary object. To properly modelthe impact force the deceleration of the vehicle after impactneeds to be found. The research found that the human bodywill pass out at loads much higher than 9 times the force ofgravity or 9 Gs. A value of 10 Gs was set as the goal pointfor an extreme worst case collision. Loads are only applied at

one end of the chassis because application of forces at oneend while constraining at the other result in a more

conservative approach because there would be increasedbending loads due to larger unsupported loaded lengths.Considering worst case collision, the vehicle collides to a

stationary wall at acceleration 10Gs (Mostly achieved byplanes)

From the impulse equationF. dt = change in momentumF. dt = m. dvF = m. dv/dtF = m.aF = m*10*g = mg *10 = total weight * 10


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= 6664N

e are taking 7000N as part of our liberal approach.

his force is applied the force on the first member after the

ushing area, while restraining from the back side.aximum Stress obtained from FEA analysis was less thane yield strength of the material, so the vehicle is safe foront collision.

deImpact

s a side impact is most likely to occur with the vehicleready in motion so it was assumed that neither vehicleould be a fixed object. The side impact force was calculatedeping 4 Gs of deceleration which is equivalent to 2665Nr our vehicle. Side impact force is calculated /analysed bynstraining the entire one side of the frame & applying arce equivalent to & 3000N on the other side of theame.3000N force has been taken for analysis since duringllision the vehicle will decelerate at a force equivalent to

G & as the weight of the frame is 68 Kg the net force comes

ut to be same as stated above. Since the other vehiclesould also be in motion so relatively less force will act one vehicle. Thus taking 4Gs for the side impact,= 2665N

RolloverImpactAs there wont be any direct forces that would cause rollover

thus rollover impact was analyzed for 3.5Gs ofdeceleration,which is equivalent to 833N of force, but we performed teston 1000N after which the factor of safety comes out to11.195. Rollover impact determines the cornering capabilityof the vehicle without toppling. It is the measuring of

adherence of the vehicle to the ground when acted upon by aforce which intends to topple the vehicle. It is calculated byconstraining the bottom of the frame and applying a sideforce on the top of the roll hoop.

RearImpactIt was assumed that worst case collision would be seen whenthe vehicle runs into a stationary object. To properly modelthe impact force the deceleration of the vehicle after impactneeds to be found. A value of 9 Gs was set as the goal pointfor an extreme worst case collision. Loads are only applied atone end of the chassis because application of forces at oneend while constraining at the other result in a moreconservative approach because there would be increasedbending loads due to larger unsupported loaded lengths.

Considering worst case collision, the vehicle collides to astationary wall at acceleration 9Gs (Mostly achieved byplanes)F = 6000NThis force is applied at the two rear most corners of the rollcage, while restraining from the front side. Maximum Stress


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tained from FEA analysis was less than the yield strength

the material, so the vehicle is safe for front collision.

ARTMODULATION

RAKINGSYSTEM

he braking system can lock all four wheels simultaneously.e will be using 220mm axial disc brakes and double pistonlliper with each piston diameter inches for braking front

d rear wheels. Considering deceleration at 1.5G, frontynamic weight comes out to 62% after weight transferuring deceleration. For this dynamic weight, the biasingquired is 62.05% in front and 37.95% at the back. Requiredaking torque at front and rear axle is 716.63 LbFt and8.38 LbFt. For average foot pedal force of 75 Lbs anddal ratio 6.34, we are creating rear and front torque equal to05 LbFt. Using a 220 mm disc and double piston calliperdia inches and considering break pads of radial height

5 inch and coefficient of friction 0.65; our break lineessure comes out to 3363.47 Psi, which is in a considerablenge.

fter doing some market research we zeroed in on to brakellipers & disc of motorcycle considering the factors likest, availability and ease of installation. The callipers will bewered by dual master cylinders. The reason for using twoaster cylinders is to impart brake biasing and increasingfety by incorporating dual redundancy and confirmationth SAE rules. Using this system, a failure in one circuitll not result in entire braking failure. Another reason for

choosing this design was its compact arrangement. The

master cylinders mount directly to the indigenously builtpedal with pedal ratio 6.34.

SUSPENSIONSYSTEM

The suspension was designed with the main aim of keepingminimal load transfer and good straight line stability during

cornering, braking and acceleration, making the suspensionand the vehicle in general very stable. The suspension is

of Double Wishbone type with nonparallel A-arms. We haveused a longer wheelbase to maintain stability at high speedsand to minimize any handling problems. This decision gaveus reduced longitudinal load transfer with no over steer. Italso gave us more space to pack the rest of the components.

The trackwidth was measured in proportion with the wheelbase, in order to extract good lateral load transfer and cornerentry. A front track of 1524 mm and a rear track of 1498 mmwere chosen. The wheelbase is 1900 mm. For effectivesuspension design the roll centre height must decrease at

about the same rate as the suspension is compressed. Theconsiderations adopted for such a design are as follows:

1) . Clearance between the joints and the wheels and tiresshould be given utmost importance. Upper and lower balljoints are located as far as possible from each other. Sincethe spread between the points is increased, it will help in

lower forces from any load to the chassis.

2) Suspension system should be designed to carry the sprungweight of the car as well as the increased weight at thefront suspension because of the dynamic weight transfer

during braking. The squat and the lift for the rearsuspensions during acceleration and deceleration shouldbe handled.

3) Excessive KPI (King Pin inclination) makes tire contactpatch to run up the edge of the tire as it is turned, henceKPI should not be greater than 3 degrees. However, if the

KPI is less than the scrub radius which should ideally be 0will not be minimum as scrub radius will increase becauseof a decrease in KPI. So a compromise is struck betweenthe KPI and the scrub radius.

4) Upper control arm length should be optimized so thatminimum change in roll centre location comes during

bounce and roll. A shorter control arm than the optimizedlength will make the camber gain progressive.

5) Lower control arm should be as long as possible becauseit helps in reducing angularity the ball joints must


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accommodate as well as slows down angular change of

the suspension members as they go through their travel.

Longer Swing arm lengths at normal ride height so thatthey give minimum camber gain.

Minimum roll centre movement by controlling followingfeatures:Optimizing upper control arm lengthNo lateral movement during turnsRelative movement of roll centre with suspension travel

for best handling results. We positioned our roll centres at3.23 inches and 5.00 inches above the ground in the frontand rear respectively. We had to keep such a differencebetween front and rear roll centres so as to suit our weightdistribution ratio and make sure that the car wont jack upfrom front during heavy acceleration.

onsidering all the above mentioned factors we havesigned our suspension system with technical specificationsfollows:

or the front suspension system, roll centre height is 3.16ches and castor gain is 0.01 degrees, camber gain -0.83grees and for the front natural frequency in cycle/sec, 1.64;e spring rate comes out to 170 Lbs/in with motion ratio of427.

or the rear suspension system, roll centre height is 5.16ches, camber gain -1.46 degrees and for the rear naturalequency in cycle/sec, 2.41; the spring rate comes out to 500bs/in with motion ratio of 0.449. We are using tie rods inar suspension system to minimize toe error duringceleration and deceleration.

he suspension with the above mentioned specifications is

ailable in the market. For this suspension system, Front and

ear camber v/s dive inches, Front and Rear ToeIn degreess Roll degrees, Front and Rear ToeIn degrees v/s diveches, Front and Rear roll centre height are coming out inrmissible limit.

l above parameters are being optimized for minimum rolleer and bump steer.

STEERINGSYSTEM

A rack and pinion steering system will be used over arecirculating-ball system because of low cost, lightweight andsimplicity in design. A standard steering system of Maruti800 will be used. Human factor will also be taken inpositioning the steering system-seating interface. The mostcomfortable angle between the arms and the fore arm is 120degrees; the height of the seat in our vehicle will also beadjusted so that the angle between the arm and the fore arm is120 degrees. The steering geometry is in accordance withAckerman steering System.

The error for the designed Ackermann geometry is comingout to be 15 percent at max (Well under 20 percentpermissible limit)

Technical specifications for steering geometry:

Knuckle length - 4inch Turning radius - 9ft Outer turning angle - 23 degrees Inner turning angle - 33 degrees Steering Ratio - 4:1

ENGINE AND TRANSMISSION AND THEIRMOUNTING

The complete drive train, that is the engine and transmissionis sponsored by the SAE-INDIA. Thus, our design isaccording to the specifications provided by the organizers.

The details of the engine and transmission are:

EngineSpecifications


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he whole of the engine block has been designed consideringe dimensions as stated above thereby resulting to proper

ounting of the engine along with the transmission housingading to proper positioning of the rear axles. This will

sure no compromises regarding the stability and balance ofe formula vehicle. Keeping the serviceability of the enginemind the supporting frame members for the main roll hoop

d been bolted to the frame in accordance with the rulebook.his will allow us to remove the members whenever the

gine has to be removed for servicing.

e got the information regarding the space required forgine mounting and the position of the clips that hold thegine from our college automobile lab. The engine will be

ounted in a 31in x 26in x 33in space giving ample room forrvicing.

NNOVATION

EfficientcoolingsystemThe vehicle features wind tunnels on both sides whichincrease the velocity of incoming air by four times because ofthe area ratio and directs the air directly to the radiator, thusproducing an efficient and improved cooling.

ImprovedVisionandSafetyFor improved vision, front hoop has been shifted slightlytowards the front and a cut has been introduced in the front

bonnet for clear vision. Hand guards and shoulder guardshave been introduced for the better safety of the driver.

EfficientuseofmembersThe chassis has been designed with an aim to properly utilize

the members for mounting.

DigitalSpeedometer

COLLEGE FACILITIES FOR

FABRICATION

Our college is well equipped with CNC machines, lathemachines, CO2 MIG Welding, Electric Arc Welding, PipeBenders, Cutters, Drill machines and we have a fully

equipped Student SAE workshop with all facilities and toolsrequired for fabrication which we have utilized forfabrication of various vehicles.

CONCLUSION

Team NITJ is a well balanced team with team members with

various areas of specialization. Each member has contributedto the design of the vehicle making full use of theirspecialization. The team features a unique balance of

experience and enthusiasm. Most members have goodexperience of designing and fabricating vehicles in the

college facilities. The team also has few members who havebeen newly exposed to the complexities of designing andfabrication, hence giving them exposure to extremeengineering.The vehicle complies with all the rules and regulations set by

SAE India for the event. Doing PVC modeling before CAD


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signing allowed us to correct small glitches in our design

d optimize the vehicle design ergonomically. Designcisions were made with keeping ease of mass production,gonomics and simplicity of design in mind. The usage ofnite element analysis was invaluable to the design andalysis of the various sub assemblies of vehicle. Thealysis thus allowed optimizing the weight and strength ofe various sub assemblies of the vehicle. The analysis alsolped in arriving at final structure from base model byding and deleting members from various subassemblies tot best possible configuration to help the vehicle withstand

rious conditions that may be encountered during actualcing.he team has access to the best facilities in the collegeemises along with a SAE collegiate club workshop that willow the team to fabricate the vehicle indigenously.

CKOWLEDGEMENT

e would like to thank SAE for organizing such an event

at has given us an opportunity to realize and showcase thegineering skills that our team members have developed

ver the years. Team NITJ is highly grateful to: Prof. (Dr.) SK Dass, Director, Dr. BR Ambedkar

National Institute of Technology

Dr. Rakesh Chandra, Dean (Research andConsultancy)

Dr. Joseph Anand Vaz, Head of Department(Mechanical engg.)

Dr. Subhash Chander, Faculty Advisor, Team NITJr their assistance and encouragement on this project. Wee highly grateful to our college faculty for developing and

lishing our engineering aptitude which made us capable ofking up a project of this magnitude.

EFERANCES

1) Tune to win by Carrol smith2) Fundamentals of Vehicle Dynamics by Thomas D.

Gillespie

3) Bosch HandbookONTACT

1) Dr. Subhash ChanderFaculty [email protected]+91-9417864015

2) Amit KumarTeam [email protected]+91-9530538669

3) Pushkar SikkaTeam Vice [email protected]

+91-9872877044
mailto:[email protected]:[email protected]:[email protected]:[email protected]:[email protected]:[email protected]:[email protected]:[email protected]:[email protected]

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Preliminary Design Report.docx