SREC

7/27/2019 SREC

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SRI RAMAKRISHNA ENGINEERING COLLEGE

Baja SAEINDIA 2012

Design Report

7/27/2019 SREC


BAJA SAEINDIA 2012 Design Report

Team registration ID: 57991

Author: R. Raamprashaath

Author email ID: [email protected]

INTRODUCTION

This event aims at challenging the

budding engineers and makes them face

real time challenges in designing and

fabricating BAJA vehicle. Our vehicle

serves its purpose by compiling with all

rules set by the BAJA SAEINDIA.

TECHNICAL SPECIFICATIONS

OVERALL DIMENSIONS & WEIGHT

Overall length 2050 mm

Overall height 1535 mm

Overall width 1603 mm

Track width (front)

(rear)

1400 mm

1400 mm

Wheel base 1476.5 mm

Ground clearance 254mm

Kerb weight 350 Kg

ROLL CAGE

Material ASTM A106 B

Construction Tubular

Type of weld GTAW (TIG)

Number of welds 62

Co-author: B.Prasanth

ENGINE

TypeFour stroke petrol

engine

Model Briggs & Stratton

Displacement 305 cc

Maximum

power10 HP @ 4000 rpm

Maximum

torque18.65 Nm @ 2600 rpm

Mounting Rear transverse

TRANSMISSION

Type Rear wheel drive

Gear boxConstant mesh (4

forward + 1 reverse)

Model Mahindra Alpha

Gear & gear

ratio

I 31.45

II 18.7

III 11.4

IV 7.35R 55.08

SUSPENSION

Front Parallel unequal

wishbones

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RearParallel unequal

wishbones

Shock absorbersMonotube inverted gas

shocks

Travel 100 mm

STEERING

TypeVariable rack and

pinion

Model Maruti 800

Steering ratio 14:1 to 20:1

Turning radius 4 m

Lock to lock

turns3

BRAKES

Front Disc brakes

(200 mm)

RearDisc brakes

(200 mm)

Braking distance 10 m

Bias 70:30

PERFORMANCE

Acceleration 0.55 m/s2

Grade ability 26.430

Maximum speed 41.25 kmph

SAFETY

Centre of gravity 488 mm

Static stabilityfactor

1.51

Roll over

probability15 %

3D VIEW

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ROLL CAGE DESIGN

The objective of the roll cage is to

accommodate the driver and other

components of vehicle and protect them

under collisions. The overall roll cagegeometry is guided by strict rules which

are constantly referred to ensure rule

book compliance and the driver safety is

given top priority.

The initial design was made using

the guidelines given in rulebook. A PVC

prototype was made to ensure the space

proficiency. This design is developed

considering the aesthetics and safety. Thisstructure is then modified to make it easy

to manufacture. The entire design was

done using Pro/E software.

MATERIAL SELECTION

This PVC model is further developed into

a structure with the help of finite element

analysis.

MATERIAL PROPERTIES

Material ASTM A 106 B

Yield strength 463.77 N/mm2

Ultimate strength 552.43 N/mm2

Young’s modulus 205 GPa

Outer diameter 33.4 mm

Wall thickness 3.38 mm

Welding preferred TIG

MATERI AL

TENSILE

STRENGTH

(N/mm2)

COST/

m(Rs.)

WELDA

BILITY (Scale 5)

AVAILA

BILITY (Scale

5)

AISI 1018 370.2 600 5 4

AISI 4130 448.8 2200 1 1

IS 1239 407.45 765 4 5

ASTM

A106 B

463.7 273 4 5

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ANALYSIS

The roll cage designed is finite

element analyzed using ANSYS software

and features are added suitably to

strengthen the structure.

TEST LOADRESULTS

STRESS F.S

Front impact

22540 N 221.336 2.03

Rearimpact

22540 N 205.49 2.19

Sideimpact

11500 N 219.347 2.05

Roll over

test 9000 N 211.462 2.13

Heave test 4500 N 159.07 2.83

Front

bump test 5250 N 75.53 5.95

Rear

bump test 5250 N 95.599 4.7

FRONTAL IMPACT TEST

The dynamic energy of the masses under

impact is given by

E = 0.5 * {m1m2/m1+m2} * (u2-u1)2

The impact force is given by

F = E/t

Where t is the impact time; t = 1s

Mass of vehicle = 460 kg

Relative velocity = 50 kmph

F = ¼ * 460 *142 * 1/1 = 22540 N

The above determined load is applied on

the frontal area of roll cage and the

stresses and deflection values are found

satisfactory.

REAR IMPACT TEST

The impact force to be applied is given by

F = ¼ * 460 * 142 * 1/1 = 22540 N

This load is applied on the roll cage and

the stress values and deflection are found

satisfactory.

SIDE IMPACT TEST

The impact force to be applied is given by

F = ¼ * 460 * 102 * 1/1 = 11500 N

This load is applied on the roll cage and

the stress values and deflection are found

satisfactory.

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ROLL OVER TEST

This test is performed to analyze

the structure under rollover impact

conditions. The vehicle is pretended to

roll and the load is applied on the top

members of structure.

The impact force is given by

F = 2 * 460 * 9.81 = 9000 N

HEAVE TESTThis test is performed to strength

of the base of vehicle. The static force

applied is given by

F= 460 * 9.81 = 4600 N

BUMP TEST

This test is conducted to check the

structure when the vehicle lands on a

single wheel after a bump. The impact

force for both front and rear bump test is

given by

F = ½ * 460 * 9.81 *2.32 = 5250 N

FRONT BUMP TEST

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REAR BUMP TEST

MANUFACTURING METHODOLOGY

The joints that are to be welded

are edge prepared prior to welding

process. The profile on the edges is drawn

using TUBEMITER software. The cut

tubes are held by clamps on a firm base

and are welded in order to ensure

accuracy. The welded regions are

immediately covered with sand to

prevent air cooling of the welds. This

decreases the internal stresses that would

result due to welding.

SUSPENSION DESIGN

The suspension gives the driver

the comfort and isolates the components

from shocks that arise due to road

conditions. The suspension used is

parallel unequal double wishbones (both

front and rear) as this could perform

better than many other types. The

suspension is set to perform well in the

off-road conditions.

MATERIAL PROPERTIES

Material ASTM A 106 B

Yield strength 288.81 N/mm2

Ultimate strength 428.56 N/mm2

Youngs modulus 205 GPa

Outer diameter 26.7 mm

Wall thickness 2.87 mm

Welding preferred TIG

The initial design of the arms is

then modified to have to have no bends to

increase its strength. The arms are finite

element analyzed using ANSYS software.Initial design

This design is analyzed usingANSYS and found that it doesn’t possess

adequate strength during impact. Hence a

new model is developed and analyzed

using ANSYS.

FINAL DESIGN

Lower

arm

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ANALYSIS

Weight of vehicle including driver

= 460 kg = 4512.6 N

Number of arms = 4*2 = 8

Assuming equal forces on each arm, static

upward force on each arm is

F = 4512.6/8 = 564.075 N

The dynamic load on each arm is

Fd = 2*564.075 = 1128.15 N

Hence it is taken as 1200 N. Also

due to rolling motion and friction, there is

a load in the direction of motion which isestimated as 0.3 times the normal load.

Fr = 0.3*1200 = 360 N

These loads are applied on the end

of arm and stress values are found out.

ARM CONDITION STRESS F.S

Upper

All DOF = 0 at

mountingpoints;

Fd, Fr at rod end

136.874N/mm2

2.11

Lower

All DOF = 0 at

mounting

points;

Fd, Fr at rod end

139.352

N/mm2 2.08

MANUFACTURING METHODOLOGY

The A arms are TIG welded with

the help of fixtures and holding

equipment. The welded regions are

immediately covered with sand to

Upper

arm

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prevent air cooling of the welds. This

decreases the internal stresses that would

result due to welding.

SHOCK ABSORBER

The shock absorber absorbs the

impact loads that act on the vehicle. The

shocks that are light with considerable

travel are chosen for the purpose.

The custom made shocks don’t suit

the purpose as it has lower elasticity than

that of automobile springs. Hence

readymade springs are used in the

shocks. They are mono tube inverted gasfilled shocks.

STEERING

The steering system gets the

vehicle into the desired direction. The

steering system used must avoid over

steer and must be rugged to perform in

off-road conditions.

TYPEWEI

GHT

EASE

OF

MOUNTING

COSTSENSITI

VITY

Variablerack and

pinion

Less High Less Medium

Recircula

ting ball

type

High Low HighVery

high

Central

rollerand rack Less

Mediu

m

Mediu

m High

The steering chosen is variable

rack and pinion as it suits the purpose

better and is easily available.

STEERING CALCULATIONS

The steering geometry and

mounting points are given in Susprog 3D

and the lock angles are found out.

Inside lock angle, ϴ = 18.230

Outside lock angle, φ = 26.840

Rear wheel track, a = 1400 mm

Wheel base, b = 1476.5 mm

Distance between pivot centers, c = 1120

mm

Turning radius of inside front wheel

= (b/sin φ) + (a-c)/c = 3300 mm

Turning radius of outside front wheel

= (b/sin ϴ) + (a-c)/c = 4700 mm

Steering ratio = 14:1 to 20:1

Lock to lock turns = 3

Overall turning radius = 4 m

The manual variable rack and pinion

steering of Maruti 800 is used in our

vehicle.

BRAKES

The disc brake of TVS Apache is

chosen for all wheels. The discs are light

in weight and provide a good brakingperformance. The master cylinder of

Maruti 800 is used to provide the

necessary braking force to all discs.

Discs used: 200 mm discs

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BRAKING CALCULATIONS

Maximum speed of vehicle,

V = 41.25 kmph = 11.46 m/s

Target braking distance = 10 m

Weight of vehicle = 460 kg = 4512.6 N

Kinetic Energy = mv2/2 = 30206.27 Nm

Braking force needed=KE/10 = 3020.63 N

Deceleration, d = Fb/mg = 6.57 m/s2

Weight distribution F:R = 40:60

Front axle dynamic load

= W1+(d*W*h)/(g*L)

Rear axle dynamic load

= W1- (d*W*h)/(g*L)

Where W1 = static weight on front axle

W2 = static weight on rear axle

W = total weight of vehicle

D = deceleration of vehicle

L = length of wheel base

Front axle dynamic load = 2712.03 N

Rear axle dynamic load = 1800.5 N

Brake biasing F:R 60:40

Braking torque T=µRPA*2n

µ - coefficient of friction

R -effective radius of discs

P –pressure applied by TMC

A-area of caliper of disc brakes

n- number of disc pads

The braking torque is found to be

sufficient to lock the wheels. The braking

circuit is diagonal split (X type) to reduce

the chances of skidding.

Stopping time, t = v/d =11.46/6.57=1.75 s

Stopping distance, S= *t – 0.5*d*t 2 = 10 m

POWER TRAIN DESIGN

The real wheel drive is used in our

vehicle as it could provide the balance

and avoid torque steer. The transmission

system used must suit the transverse

orientation of the engine. The

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transmission system of Mahindra Alfa is

chosen for the purpose. The gearbox used

is 4 speed manual constant mesh gearbox

with 1 reverse. The gear ratios are

Gear I - 31.45:1

Gear II – 18.7:1

Gear III – 11.4:1

Gear IV – 7.35:1

Reverse – 55.08:1

Transmission efficiency = 0.8

PERFORMANCE CHARACTERISTICS

ACCELERATION

(Power available to acceleration) = (brakepower * transmission efficiency) – (power

required to overcome total road & air

resistance at max speed & top gear)

(We*V*a)/(1000*G) = (P * 0.8) – (Rr +Ra)V

We – equivalent weight of vehicle

V – Velocity of vehicle

a – Acceleration of vehicle

G – Gear ratio

P - Brake power

Rr – Rolling resistance

Ra – air resistance

We = W = (If * 0.8 * G2 + Is)/r2

If = 1.265 Nm2; Is = 3.12 Nm2;

G = 7.35; r = 0.2794 m

We = 5252.9 N

Hence

(5252.9*a*11.46)/1000*7.35=6.6*0.8 –

0.775

Therefore acceleration, a = 0.55 m/s2

Time to reach 0 to maximum speed

(41.25 kmph) is 20.84 s.

MAXIMUM SPEED

V = {(N*r)/(2.65*G)} * transmissionefficiency

Where N is engine rpm

r is wheel radius in m

G is gear ratio

Maximum speed = 41.25 kmph @ 2800

rpm

TRACTIVE EFFORT

Tf = 3603 * 0.8 * Pe/V

ROLLING RESISTANCE

Rr = (a+bV) W

a = 0.015; b = 0.0016

AIR RESISTANCE

Ra = k a * A * V2

k a = 0.045; A= 0.15125 m2

GRADE RESISTANCE

Rg = Tf – Rr – Ra

GRADE

ϴ = sin-1 (Rg/W)

Using the above stated formula the

maximum grad ability of our vehicle is

26.430.

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WHEELS AND TYRES

The tires must suit the off-road

conditions. Hence ATV tires are chosen.

Specifications 22” x 11” x 8”

The four plied tires provide good

durability. The tread width, side wall

width, load handling capacity of the tires

provides greater advantages with

considerable less weight.

BODY PANELS

The rear roll hoop (RRH) and the

base members are supported with the MS

sheets. The side panels are covered with

the polycarbonate sheets to decrease the

weight of the vehicle and improve

aesthetics. These sheets provide goodvisual effects and ease the painting works.

DRIVERS ERGONOMICS

The driver is provided a good room for

his works. The driver cabin is designed to

accommodate the largest member of our

team with adequate clearance from walls.

The racing seats with racks are purchased

which provides the driver good comfort

even during action.

SAFETY EQUIPMENTS

The vehicle is equipped with a

temperature sensory circuit which stops

the engine during any fire accidents. This

system automatically actuates kill switchif the local temperature increases beyond

a certain limit which may lead to fire.

The temperature sensors and

thermocouples attached at various points

on vehicle constantly measure the local

temperature. If the temperature exceeds

the predefined value the sensor actuates

the kill switch and stops the engine. This

prevents the further fire accidents.

Temperature

sensor

µ Controller

Kill switchEngine

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HORN CIRCUIT

The following block diagram gives

the horn circuit being installed in our

vehicle.

LIGHTING CIRCUIT

The following diagram gives the

lighting circuit which includes a reverse

light being installed in our vehicle.

ENGINEERING BILL OF MATERIALS

PART/SYSTEM SUB-SYSTEM

Engine

Fuel tank

Air filterExhaust

TransmissionGearbox

Clutch

Drive TrainHalf Shaft

Hub

Steering

Rack and pinion

Steering column

Steering wheel

SuspensionA-Arms

Shock absorbers

FrameASTM A106 B tubes

MS sheet

BodyLexon

polycarbonate

Brakes

Discs

Caliper

TMC

Brake lines

Safety Equipment Temperature sensorFire extinguisher

Electrical

Equipment

Lights (brake &

reverse)

Horn

Kill switch

WheelsRims

Tires

ClampsFasteners

Bushes

Miscellaneous Accessories

ACKNOWLEDGEMENT

Team phoenix would like to express sincere

gratitude to the following persons for their

guidance and support.

Mr.C.Natarajan, Faculty advisor

Dr.P.Karuppuswamy, HOD

Dr.R.Radhakrishnan, Principal

BAJA SAEINDIA selection committee

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REFERENCES

BAJA SAEINDIA Rule book 2012

“Design of Machine Elements” by R.S.Khurmi

& J.K.Gupta

“Automobile Engineering” by Dr.Kirpal Singh

“Race car vehicle dynamics” by Milliken

“Fundamentals of vehicle dynamics” by

Thomas D Gillespie

“Tune to win” by Carroll Smith

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