ABSTRACT

This project required immense research and study of

various systems incorporated into a formula race car

and also the design methodologies used in todays industrial scenario. It also included the study of the

previous models built by other teams. It challenged

our knowledge of the engineering principles and

practices.

The process started with the identification of the

major goals of the project and conversion of those

objectives into measurable quantities. After this

various constraints were identified. The team was

then divided into various sections and work was

allotted to each section according to their field of

expertise. The design for each component was

iterated until the desired objectives were fulfilled.

SUSPENSION DESIGN

The suspension system of a car serves a dual

purpose contributing to the car's handling and braking for good active safety and driving

performance, and keeping vehicle occupants

comfortable and reasonably well isolated from road

noise, bumps, and vibrations. However keeping in

mind the flat event track the suspension was

designed to improve the vehicle level.

Firstly the rulebook was studied to ensure

compliance to SUPRA rule. As per the rulebook the

car must have a wheelbase of at least 1525mm (60

inches) and must be equipped with a fully

operational suspension system with shock absorbers,

front and rear, with usable wheel travel of at least

50.8mm (2 inches), 25.4mm (1 inch) jounce and

25.4mm (1 inch) rebound, with driver seated. Also

the wheel size is restricted to a minimum of

203.2mm (8 inch). Once the rulebook had been

studied the goals and constraints were identified to

initiate the design of suspension geometry.

Suspension geometry is governed by kinematic laws

Team VEGA JSS Academy of Technical Education

Preliminary Design Report

SUPRA SAEINDIA 2014

of motion and a compromise has to be made

between the kinematically and practically optimum

geometry. Team VEGA decided to go with the four-

wheel independent Double A-Arm suspension

design. A wheel size of 13 inches (330.2mm) was

chosen in order to meet the demand for acceleration

as well as handling. The teams plan was to pack the entire upright and kingpin assembly within the

wheel therefore a wider wheel size with large offset

was chosen. As our wheel was 330mm in diameter

hence the upper and lower ball joints could not be

more than 300mm apart. As for the packaging of

brake assembly and the uprights, suitable clearance

was maintained to locate the lower ball joints inside

the wheel.

After putting the variables in place, kinematic design

was started. This included the length of the desired

front view swing arm (FVSA). Once this was

located, a desired location of the roll centre was

marked on the centre line of the vehicle. The basic

goal was to find the optimum location of the RC and

to minimize RC migration. Now as the vehicle is

cornering, lateral forces at the Centre of gravity

(CG) of the frame tend to create a moment about the

roll Centre, the RC hence should be as close to the

CG as possible, however a high RC would create

undesirable jacking forces. After a number of iterations a RC height of 45 mm above the ground

was chosen. Once the RC is determined, a line

between the Centre of the tire patch and the RC is

drawn to find the location of the IC, this also finds

out the upper arm angle. Finally the data is fed into a

suspension modeling software which calculates the

roll Centre location for various upper arm lengths

and body roll angles. After numerous iterations a

suitable arm length is chosen. A suitable camber

angle was decided to ensure maximum contact of

tires with ground.

CHASSIS AND FRAME DESIGN

The Chassis design is done keeping in mind the

requirements of high torsional stiffness, drivers protection, manufacturability, serviceability,

compactness and packaging of all other components.

The overall structure is compiled to reduce the

complexity and fulfillment of systems packaging and

so the suspension pick-up points are calculated

taking consideration of the diveness and Squatness

for chassis members. IS 3074 (ERW) steel

spaceframe is chosen over 373MPa Yield Strength

and Roll Hoops including Main Roll hoop and Front

Roll hoop with ASTM 106 (Seamless) due to

bending strength and basically the availability in the

desired wall thickness in nearby region was primary

reason. With optimized amount of triangulation and

keeping the weight as low as possible, the chassis is

targeted for 30 kg including brackets and mountings.

Pick-up points of suspension and engine produces

significant amounts of forces, thus they were

attached to the frame at triangulated points. The

frame is designed using CATIA V5 CAD and

analysis work is done on CATIA V5 FEA and

ANSYS 14.0. All harness and safety attachment

points are given space to the requirements according

to the Rule Book. The design is implemented to

provide load paths and stress regulation throughout

the extremities of suspension mountings including

front impact members and side impact members to

ensure complete safety to the driver. The farther

material is from the axis of twist the stiffer the frame

will be in bending and torsion. This concept is

implemented by adding Structural Side Pods to the

basic frame.

ERGONOMICS: Properly incorporating the driver

into frame design can be very difficult because of

wide variations in driver sizes. Each driver interface

has to be designed so that it is comfortable for

accommodating drivers who range in height from

1.55m to 1.90m.Comparison of different material

properties is shown below:

Material

Candidates

Design Requirements

UTS (N/m2) TS (N/m2)

Density (Kg/m2)

IS 3074 432 373 7860

AISI 4130 670 435 7850

ASTM 106 480 300 6100

AISI 1018 634 386 7800

TORSIONAL STIFFNESS: Torsional stiffness is

defined as the resistance of the structure to torsional

loads. The frame is subjected to frequent torsional

strains while cornering, this also changes the wheel

loads as calculated while designing of the

suspension. Torsional rigidity of the frame is

targeted for above 2000 Nm/degree. Otherwise

undesirable changes in camber and toe can occur if

the frame lacks stiffness. Each of the systems of a

car must be packaged within the frame. The

placement of the components limits the available

paths for tubes, which is usually detrimental to the

chassis stiffness.

FRAME FINITE ELEMENT ANALYSIS: The

assumption made in using beam elements is that the

welded tubes have stiffness in bending and torsion

and inclusion of transverse shearing effect. The

analysis was done by taking the Linear Tetrahedral

Geometry for meshing. Then results are analyzed

and iterated for Von Misses yield Stresses and

optimized accordingly for considerable factor of

safety.

Table: Boundary conditions of various tests.

STEERING SYSTEM

The next way-point in the design process is the

steering system. Steering is another important aspect

of the vehicles handling. If the system is not properly designed the wheel may toe in or out during

suspension travel, this is known as bump steer.

Sr.

no.

Test Boundary

conditions

Force moments Magnitude

1. Static Shear Clamp rear suspension

mounts

Downward force

at front

bulkhead

1440 N

2. Static Overall

Vertical

Bending

Clamp- front

and rear

suspension mounts

Uniformly

distributed

loading

1500 N

3. Static torsional

loading

Clamp- rear

suspension

mounts

Clockwise

Moment at

bulkhead side

310 Nm

4. Acceleration

Analysis

Clamp- front

and rear suspension

mounts

Force applied

towards rear

840 N

In order to minimize this event the IC of the tie rod

must coincide with that of the control arms. This

ensures that the tie rod travels in the same curvature

as that of the control arms and there is no

unintentional relative movement between the

kingpin and the tie rod.

GEOMETRY: Ackermann geometry is generally

used in production cars in order to minimize tire slip.

While this geometry is very effective in slow speed

turns, it is not suitable for high speed cornering.

During a high speed turn the inner wheel provides

for very little cornering force therefore its slip is

irrelevant and can be neglected. Most of the

frictional force is generated by the outer wheel and

therefore it accounts for much of the steering.

Parallel or even reverse Ackerman geometry is used

in these cases. A compromise between parallel and

Ackermann geometry was chosen by the team.

STEERING RATIO: Overall steering ratio is an

important parameter because it determines how

"quick" the steering is. Like many parameters,

steering ratio is partly a driver preference, but some

guidelines do exist. A very fast ratio will be more

sensitive to the drivers steering inputs, but extreme sensitivity may increase driver fatigue or make it

difficult for the driver to keep the car pointed in the

desired direction when road inputs jerk the drivers hands. At the other extreme, too slow a ratio will

require large hand movements, which is not

desirable for the tight SUPRA SAE 2014 courses.

Driver does not have to shuffle his or her hands

around which would again reduce the cars maneuverability. In order to negotiate the tightest

corners (m outer diameter) for the SUPRA SAE

circuits with less than one rotation of the steering

wheel, a steering ratio of about 8:1 was decided by

Team VEGA.

CASTER ANGLE: Positive caster angle induces a

self-cornering force that provides straight line

stability, but increases steering effort. Toe is the

angle made by the wheel with respect to the

longitudinal axis of the vehicle. Static toe of front

and rear wheel is taken as zero to maintain

directional stability.

TURNING RADIUS: According to the rulebook, the

turning radius of hairpin turn is 4.5m. So we

designed our steering geometry to take a turn of

minimum 2.5m radius of circle. Table below shows

the different steering and suspension geometry.

BRAKES

Brakes of a vehicle matter a lot in the performance

of a vehicle. To get maximum heat dissipation team

decided to use disc brakes. Parameters which define

the performance of braking system were defined and

calculated below.

WEIGHT TRANSFER: To get a desire tractive

force on drive wheels (i.e. rear wheel in our car) we

fixed the static weight ratio of front and rear as

40:60 and it becomes 54:46 at the time of retardation

in brake test as given in rulebook.

BRAKE EFFICIENCY: Braking efficiency is

defined as the ratio of maximum wheels-unlocked

vehicle deceleration to tire-road friction coefficient.

The braking efficiency expresses the extent to which

a given tire-road friction coefficient available to a

vehicle is transformed into maximum wheels-

unlocked deceleration. Brake system is designed as

to achieve maximum retardation of g .The distance travel by the car from 40kmph to 0kmph is

6.9meters.For (coefficient of friction)=0.7,brake

efficiency is 88% which is fairly good and it

becomes 100% at =1.

BRAKING FORCE: Brake system is designed to

achieve the ratio of 1.27:1 braking force on disc by

calipers in front and rear wheels (which obtained

according to the longitudinal weight transfer).

Selected pedal ratio was 4:1 due to which pedal

force require for this is 207.5N which can be easily

apply by the driver.

Rotors having diameter of 240mm and 220mm were

selected to use in front and rear disc respectively.

KPI 3

CASTER 4 positive

CAMBER 2 negative

TOE 0

STEERING RATIO 8:1

ENGINE AND DRIVETRAIN

ENGINE: For the purpose of SUPRA SAEINDIA

2014 competition our team has chosen an engine

from a HONDA CBR 250r motorbike. Our teams

intention is to build a small and a very light Formula

car and this compact power train unit perfectly fits to

our car conception. It is a four stroke water cooled

single cylinder SI engine with a displacement of

250cc and it weighs just 35.4 kilograms. This engine

will be overcharged by the intake manifold using the

ram wave effect.

Engine specification:

Displacement 250 cc

Bore 76 mm

Stroke 55 mm

Compression ratio 10.7

Engine power 25bhp@8500rpm

Engine torque 22.9@7000rpm

DRIVETRAIN: The drivetrain system consists of

every component from the engine output shaft to the

wheels.

Our goal is to achieve a speed of 80kmph because in

the endurance race, average speed lies in the range

of 47-57kmph and usually we dont see speed greater than 80kmph although the maximum speed is

105km/hr. Looking at our speed calculation, we see

that our car is capable of reaching this speed with the

final drive ratio of 4:1(56/14).Table shows the

different gear ratios of drivetrain with maximum

traction force, acceleration and velocity for peak

engine torque.

gear Gear

ratio

Tractive

force(N)

Acc.

(m/s2)

Velocity(m/s)

1 3.33 3443.113 10.43 4.72

2 2.117 2188.909 6.63 7.43

3 1.571 1624.363 4.92 10.02

4 1.304 1348.94 4.08 12.07

5 1.115 1152.87 3.49 14.12

6 0.962 994.627 3.01 16.37

Fig.2.1 shows the plot between tractive force and

road speed. The "Constant Engine Power" line is

equal to the maximum power of the engine, which is

the upper limit of tractive effort available, less any

losses in the driveline. For maximum acceleration

performance the optimum shift point between gears

is the point where the lines cross. The area between

the lines for the different gears and the constant

power curve is indicative of the deficiencies of the

transmission in providing maximum acceleration

performance.

INTAKE RESTRICTOR DESIGN: The restrictor is

a very significant part of the intake system being

modeled. The restrictor is the ultimate restriction on

the amount of air which can flow into the intake

system, and thus, the amount of power produced by

the engine. Consequently this segment of the intake

manifold is the logical place to commence

simulations.

A thorough understanding of the flow through this

section will allow the team VEGA to improve the

design as much as possible, giving the best possible

air flow into the plenum. In order to get the

maximum mass flow rate and minimum pressure

drop across the restrictor, converging-diverging

geometry is selected with throat section of 15mm.

From the data gathered through the numerous

simulation in CFD fluent, it can be observed that the

optimized value for converging and diverging angle

of restrictor were found to be 10 and 6

respectively. Optimization of converging-diverging

angles for minimum pressure drop is shown in

tabular form:

Row value Diverging angle

column value

4 6 8 10 12

Conv

ergin

g

ang

le

8 0.21 0.192 0.198 0.21 0.22

10 0.2 0.193 0.195 0.214 0.22

12 0.199 0.197 0.193 0.196 0.198

14 0.22 0.196 0.20 0.205 0.213

15 .192 0.184 0.21 0.196 0.20

1300 mm

377.7 mm

FRONT VIEW

CAD MODEL

508 mm

TOP VIEW

SIDE VIEW

330 mm

43.29