Paper Number

Team: VAJRA

Ashish Kumar SinghDesign Team Captain

Chitransh AgnihotriTeam Captain

Copyright © 2009 SAE International

ABSTRACT

This report has the details our work and the procedure and methodology we use for this event’s preparation. Right from the first day we have faced so many problems. But we kept our cool, applied logical and analytical approach for them, this developed our personalities as we were now beginning to learn how efficiently a team can work and the output is this report. Creating a concordance we have made a concept ATV vehicle within the BAJA Rulebook and have taking care of all the failures.

INTRODUCTION

Our approach for this competition was to bring out a successful vehicle with some new innovations. The Preliminary Design Report is outcome of our approach towards this competition. Before beginning the design we must know the needs which where required for the ATV, that is why we put ourselves in the shoes of the customers who are going to purchase this vehicle.

REQUIREMENTS OF A VEHICLE:

1. Cost of the vehicle. 2. Looks 3. Endurance or Life.4. Parts easily available for maintenance.5. Speed and Acceleration.6. Maneuverability.7. Mass and Overall dimensions must be less.

With this we had a view of our ATV. This started our mission and we set up some parameters for our work, distributed ourselves in groups.

SUB-TEAMS FOR DESIGN

● Roll Cage ● Transmission ● Brakes and Wheels ● Suspension ● Steering

Our main aim was to work under the guidelines of the rule book, and use the maximum limits.

PARAMETERS FOR VEHICLE

● Achieve an acceleration of 3m/sec2

● Restrict the weight to 200 kgs. ● Minimum wheelbase of 54 inches. ● Total length min.6 feet and max. 7feet ● Ground clearance of 8 inches. ●Total height of 48 inches(with clearance above head) ● Avoid Over-engineering.

FINITE ELEMENT ANALYSIS

With using Autodesk Inventor we have also made a detailed FEA of the Roll cage design, which was successful. This enhanced our learning approach and limits for practically analyzing the elements as done in industries. This experience is very amazing as this is something which we never would have practiced if it was not for this competition.

MAIN SECTION

ROLL CAGE

Objective

The function of roll cage is to protect the occupant and provide the support for all the operator control system, front and rear suspension, power train. The objective of the frame design was to satisfy these functions while meeting the SAE regulations with special considerations given to safety of the occupants, ease of manufacturing, cost, quality, weight, and overall attractiveness. Other design factors included durability and maintainability of the frame.

Design

The IET DAVV Baja team designed a vehicle frame with primary emphasis given to factors of safety, durability, performance, and manufacturability while abiding by requirements established by ASIA BAJA 2010 rulebook. Some of the goal design points are 1. Factor of safety =2.52. Overall chassis weight = 80 kg3. Least additional members for strength and support4. Maximum roll cage stability (as the dimensions of roll cage are decided after the full analysis of Vehicle dynamics)

Safety

The components of the frame are the RRH, LDB, RHO, FBM, LC, LFS, SIM, FAB, and FLC, Per SAE Competition Rules, the RRH, LDB, RHO, FBM, and LC material properties were required to have a bending stiffness and a bending strength equal to or greater than that of 1018 steel with an O.D. of 1 in. and a thickness of 0.12 in. Members LFS, SIM, FAB, and FLC were required to have a minimum wall thickness of .035 in and a minimum O.D. of 1 in. All frame members with a bend radius greater than 6 in. may be no longer than 28 in. unsupported. Clearance guidelines dictate a minimum of 6 in. vertical distance from the driver’s head to the bottom of the RHO and 3 in. clearance between the rest of the body and the vehicle envelope. The SIM is designed to give the occupant extra security during a side impact on the vehicle and to reduce the possibility of the driver leaving the cockpit. The SIM is bent outward from the car at 10 degrees and curved ribs vertically attach the SIM to the LFS which gives a strong and spacious enclosure for the driver

Analysis The IET student team’s skill set included some familiarity with static, linear, elastic FEA using Inventor The analysis was performed for several impact scenarios including: Nose impact (See Figure 3), Side (at driver’s location), Side (at nose), Top rear, and Top corner. Analysis indicated stresses below the yield strength of mild steel (207.0 MPa) for all scenarios

except the top impact study which showed a maximum stress of 570 Mpa. Based on these results, reinforcements are to be added to the top.Material data Steel, Mild

Properties Values

Young's Modulus 2.2e+005 MPaPoisson's Ratio 0.275Mass Density 7.86e-006 kg/mm³Tensile Yield Strength 207.0 MpaTensile Ultimate Strength 345.0 MPa

TRANSMISSION

We are planning to use a synchromeshed transmission with a Piaggio Ape transmission with these Gear Ratio’s in Reverse OrientationReason for Reverse orientation

1.) High acceleration is achieved around 1.7 times higher.

2.) Advantage in hill climbing events and maneuver-ability.

3.) Faster Cornering acceleration.

Gear Ratio’s Speed @ 3000 rpm

Dia 22. Dia. 24

First Gear 1:55.08. 5.7 6.3

Second Gear

1:32.72 9.65 10.6

Third Gear 1:19.95 16 17.4

Fourth Gear

1:13.40 24 27

Reverse Gear

1:31.48 10.3 11.2

Also we will be using 2 sprockets and a chain which will take output from Differential end of transmission and take it to axle.

Reason for choosing Chain Drive:1.) Maximum speed will be around 40 which is appreciable.2.) If not used the thrust can overturn the vehicle.

This will decrease the final drive ratio by 1.4 times, as diameters of sprockets are in these ratios and maximum speed will reach 27 * 1.4 = 37kmph (at 3000 rpm).So at looking at these calculations we have analyzed that a 24 inch dia wheel is needed by this sort of transmission for a proper speed.

SUSPENSION

A Suspension acts to provide cushioning action to the driver by absorbing the shocks from the road and also helps the tires to maintain good traction.

Demands from a good suspension system?

○ Structure. ○ Suspension system ○ Stiffness - Design for maximum torsion Stiffness and least weight. ○Provide sufficient ground clearance. ○Within track range. ○Design to provide typical tunable features.

Complexity

Design mounting such that some extend of adjustment is possible, like

1.) Suspension. 2.) Ride height/ Suspension travel. 3.) Body attitude. 4.) Wheel loads/springs. 5.) Dampers. 6.) Static settings of wheels alignment geometry. 7.) Roll centre HT front and rear. 8.) Swing arm length. 9.) Height of steering rack.

Failure1.) Failure occurs if they are not able to

isolate the driver from the shocks or if they are so soft that they compress to their solid length while working.

2.) Spring damper may buckle if length is more. 3.)Spring compresses to solid length under any load.

Our Vehicle design

We have chosen Independent type suspension in both Front and Rear because:

1.)Little space requirement. 2.) A kinematic and/or elastokinematic toe-in change, tending towards under steering is possible. 3.) Easier steer ability with existing drive.

4.) Low weight. 5.) No mutual wheel influence, thus good road holding, especially on bends with an uneven road surface

Independent 1.) In Independent type firstly, we thought

using unequal double wishbone suspension in both front and rear. But now we are planning to adapt different types in front and rear.

Front:

In front we will use the widely used double wishbone suspension.

1. It gives more movement of the tires and to the spring than Mac person strut type.2. We can distribute forces at different point on roll cage.3. Desired camber angle, castor angle and ground clearance can be achieved.4. The double A-arm uses solid, rigid control arms to mount the knuckle to the chassis. These arms prevent deflection during cornering which ensures that the steering and wheel alignment remain consistent.

Rear:

In rear we are planning to use swing axle type suspension with including central positioned suspension

1. It gives more movement of the tires and to the spring than double wishbone type.2. We can distribute forces at the centre along with sides of roll cage body.3. Desired camber angle, castor angle and ground clearance can be achieved.4. Ride Quality: By decoupling the front wheels and not by mounting the chassis on a solid beam, there is better ride isolation between the sprung and unsprung masses providing improved ride characteristics and more predictable suspension response.

Dimensions

Arm lengths will be according to the designing and fitting during fabrication.

Front:

Spring length: 230mm

Total length(spring + dampers): 356mm

Allowable travel of the spring : 75mm

Maximum travel of the spring: 92mm

Mean coil diameter:58mm

Wire diameter: 12mm

Spring stiffness(K): 32N/mm

No. of turns: 10

Rear:

Side Spring length: 320mm

Side Allowable travel of the spring: 120mm

Stiffness (K): 25N/mm

Centre Spring length: 265mm

Centre Allowable travel of the spring: 51mm

Spring stiffness (K): 35N/mm

Mean coil diameter: 70mm

Wire diameter: 12mm

No. of turns: 10

STEERING SYSTEM

The purpose of the steering system is to provide directional control of the vehicle to the driver with minimum input. While designing the steering system the constraints that we possessed were centre alignment of steering system, track width, human effort at the steering wheel and the desired response of the steering system. A Rack and Pinion steering was chosen over worm and sector and re circulating ball, due to its light weight, simple design and low cost. Also its relatively small size in the top view makes it easy to mount in comparison to the others. Very less play due to limited number of joints was also an important factor.

The steering system of Maruti 800 satisfies the aforesaid and also fits our dimensions.

Calculations/Dimensions:

(As calculated by satisfying dynamic stability equations)

Wheelbase=1524mm

Track width=1270mm

Steering angle

Inside wheel angle, 1= 38 deg.

Outside wheel angle, 0= 25 deg.

Formula used

tan1= L/(R-t/2)

Thus, turning radius R= 2667mm.

BRAKING SYSTEM

The criterion for designing the brakes stated as per the rule book is that all the four wheels should lock simultaneously as the brake pedal is pressed.

Dynamics:-

For designing the braking system, we will have to calculate the dynamic weight using the formulae as given below

Front axle dynamic load = w1+(/g)*W*(H/L)Rear axle dynamic load = w2- (/g)*W*(H/L).Where,w1=weight on the front axle in the static condition. w2=weight on the rear axle in the static condition.g=acceleration due to gravity.W=total weight of the vehicle.H=height of the centre of gravity.L=length of the wheel base.=deceleration of the vehicle.

Some formulae that we used for designing our brakes :

T(disc)= W1*(f/g)*R1+W2*(f/g)*R2.T(disc)=*R*(P*A)*2*no. of disc brake.Where,T(disc)= frictional torque on the disc.f=deceleration.W= weight of the body.R= Effective radius of the disc.R1=radius of the front tyre.R2=radius of the rear tyre.P=pressure applied by the TMC.=coefficient of friction.A=area of calliper for disc brake.

Components:-

Tandem master cylinder ,oil tank, proportioning valve, oil lines, disk valves.

Actuation System

The system is hydraulically actuated, via a brake padel which in turn generates a pressure in the master cylinder, which about 50 kPa, this pressure transmitted via the oil carrying line to the brakes.

Wheel brakes

All wheels are locked at the time of brakes via disk brakes. We are using disk brakes on all the four tyres to simultaneously lock them. The disk assembly consist of callipers, disk and friction pads. Two independent diagonal lines are used, in order to provide braking in case of failure of one line.

DIAGRAMS

Diagram 1 Rear Suspension (Swing Axle)

Diagram 2 Front Suspensions (Double Wishbone)

FINITE ELEMENT ANALYSIS We have used Autodesk Inventor for Stress Analysis.

Diagram 3. Lateral Stress analysis

Diagram 4. Rear End Analysis

Diagram 5. Middle Frame Analysis

Diagram 6.

CONCLUSION

With these analysis we conclude our Preliminary report. We have considered all the factors that can be applied

on the vehicle in an actual working conditions. We will make more analysis after this report which we will present before the competition.

ACKNOWLEDGEMENT

We are very thankful to Society of Automotive Engineers for organizing such an event which provides a great platform to students to explore their talent.

Also our college facultiesDr Ashesh Tiwari Sir (HOD Mechanical)Dr. Govind Maheshwari Sir (Faculty Advisor) Er. Vijay Kumar Karma Sir (Faculty Advisor) For providing us college resources and motivating us.

CONTACT

Raghvendra SinghMechanical 4th YearIET DAVVRaghvendra.mech2010@gmail.com

Ashish Kumar SinghMechanical 4th YearIET DAVVashish.mech2010@gmail.com

ChitranshMechanical 3rd yearIET DAVVChitransh.a2011@gmail.com