design reportof baja sae india -2010

Institute Of Technology And Management Gurgoan, Haryana SAE Baja Asia 2010

The Techie Tyros

Design Report 2010 DESIGNED BY

Vikrant Dalal Vice-captain and Head of Design Team

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#TTT-3 SAE BAJA ASIA 2010 Design Report Vikrant Dalal Vice-captain, Head of Design Team Copyright © 2009 SAE International

1.0 ABSTRACT

5.

Wheel base – 130 cm or 52 inch approx

The objective of the Baja competition is to design a Baja all-terrain vehicle that embodies innovation, simplicity and functionality, delivering high performance and safety at a reasonable price. This report details the considerations, functions and processes behind the separate vehicle subassembly

6.

Braking distance – 1400 cm

7.

Turning radius – 240 cm or 96 inch

3.0 MAIN SECTION 2.0 INTRODUCTION The design of Baja 2010 is divided into follow section: Baja-2010 is an international competition sponsored by the Society of Automotive Engineers (SAE). Engineering students are given a challenge to design, simulate and manufacture a “fun to drive”, versatile, safe, durable, and high performance off road vehicle. The Techie Tyros 2010 Baja team consists of 22 undergraduate students in Automotive and Mechanical Engineering. The goal of the 2010 car is to improve on some of the key areas that have caused the team problems over the last few competition years. These areas are: suspension, steering, driveline, hub and fabrication tolerances. tolerances. It was decided decided that, while making components lightweight is important, strength and durability of key components would not be sacrificed for weight reduction. All subassemblies and components were researched and designed to meet pre-established team expectations. For designing, simulation, analysis and optimization of the vehicle components various software such as Pro-E (design and analysis), Cosmos (analysis and simulation), Optimum K and K and suspension suspension analyzer (Suspension design and analysis), ADAMS and ADAMS and IPG IPG car maker (vehicle maker (vehicle dynamics) are used.

1.

CHASIS AND ANALYSIS

2.

ENGINE AND TRANSMISSION

3.

TYRES

4.

BRAKES

5.

STEERING

6.

SUSPENSION

7.

HUB DESIGN

3.1 CHASIS AND ANALYSIS The kind of body we are required to manufacture is a unitized body. The roll cage is of utmost importance for us as it would be the one which would provide safety to the driver, mounting points for various systems and even ergonomics and looks to the vehicle.

3.1.1 MATERIAL The design targets of our vehicle for Baja 2010 are as follows:

The material used in vehicle must fulfill the SAE Baja





Table 1: Material property MATERIAL

YIELD STRENGTH (KSI)

MODULUS OF ELASTICITY (KSI)

COST PER METER (RS)

ELONGATION AT YIELD POINT (%)

AISI 1018

53.7

29700

600

15

AISI 1020

42.7

29700

2200

36

IS 1239

59.12

29700

765

18.5

AISI 4130

65.1

29700

2500

25.5

83 82 81 80 79 78 77 76

2500 ) s 2000 R ( 1500 t s o 1000 C 500 0

) G K ( t h g i W

AISI 1080AISI 1080AISI 1020 1020 IS 1234 1234 AISI 4130 4130

cost(*10)

After running all five analyses it was found that there is a need of additional member. After having added these members, a second analysis using identical loading constraints was completed and results of these tests are shown in table 2. For front collision test stress diagram and displacement diagram is shown in figure 2 and 3. Table 2: FEA Analysis results

Graph 1: Weight and Cost comparison 3000

In order to optimized the strength, durability and weight of Chassis cosmos was used to analyze the chassis for all six loading condition. The six analysis tests conditions are front impact, side impact, rollover impact, heave and the loading on the frame from the front and rear shocks shock s

Type of case

Force applied

Result

Front Collision

4500 KN

Passed

Side Collision

1200 N

Passed

Rollover

1800 N

Passed

Front Bump

810 N

Passed

weight

Figure 2: Stress analysis for front collision AISI 4130 and IS 1239 part-1 having good yield strength will allow the usage of tubing with smaller wall thickness. This will in turn reduce the weight of our chassis. Also 4130 and IS 1239 part-1 are more ductile than other materials so it will deform more before its ultimate failure. But cost of per meter length of 4130 is 2.5 times more expensive IS 1239 part-1. So considering the above said factors we have chosen IS 1239 part-1 pipes to be used for our chassis.

3.1.2

FEA ANALYSIS

The initial design is shown in the Figure 1. Some notable features are the fact that the design consists of 4 main members: the roll hoop, the horizontal hoop, and the two perimeter hoops. As mentioned above the design was made using the Pro-E solid modelling package. Figure 1: Roll cage model in Pro-E

Figure 3: Stress displacement for front collision





Comparison between previous years roll cage design is done and the results are shown in table3. Table 3: Comparison of pervious 3 years design 2007-BAJA ROLLCAGE DESIGN

2008-BAJA ROLLCAGE DESIGN

2010-BAJA ROLLCAGE DESIGN

we are using M&M champion transmission. To increase

the torque following options were available: 1. Manipulation of power transmission outside the gear box using gears, sprockets and chain. 2. Engaging the reverse gear lever while driving in all the forward gears and using the first gear in forward as reverse gear. 3. Using the transmission system in normal conditions.

SAFETY

Poor

High

High

Average

High

High

Poor

Good

Very good

COMFORT ERGONOMIC

SPECE FOR ELECTRONIC DEVICES

More

Less

Sufficient

To heavy

Medium

Light

High

Low to high

Low

9/10

4/10

8/10

WIEGHT COST OF ROLLCAGE

STANDARDIZATION

We decided to work on the 3rd option due to following reason: 1.

We were able to check the weight

2.

Reduce the cost of the vehicle as we avoided the use of additional gears, sprockets and chains.

3.

We used standard parts, thus increased the reliability of the transmission system.

To find the speed of the vehicle corresponding to different gear ratios, the formulae used is Velocity on road =

3.2 ENGINE AND TRANSMISSION A quick look at the engine: Power - 8 kW at 4400 rpm

2 π ×N×R×60 1000×

Where, G=gear ratio N=revolutions per minute R=outer radius of the tire in meters. Some of our calculations for normal orientation are as follows:

Max Torque – 19 Nm at 3000 rpm Table 4: Normal orientation Engine was given to us. Thus we had a little choice while working on engine. Configuration of our vehicle would be rear engine rear wheel drive. We decided to keep the maximum speed of the vehicle at 60 km/hr as the vehicle is not about larger speed but greater torque and stability. As per the rules of the competition, the engine cannot be modified in any way. This restriction causes the design emphasis to be placed on the choice of transmission. For the transmission we have several options: A manual transmission (4 or 5 speed): this s ystem would allow the driver to select the right rig ht gear from the available gears allowing more control over the vehicle. This is seen on most manual cars with a standard “H” pattern.

Final Gear Ratios

Speed (km/hr)

Speed (km/hr)

First

31.45:1

0.65D

14

16

Second

18.70:1

1.109D

24

27

Third

11.40:1

1.82D

40

44

Forth

7.35:1

2.82D

60

68

Reverse

55.08:1

0.38D

10

9

D=22 inch

D=24 inch





constant. Thus, for better economy, the range of speed in each gear, for the driving tires of O.D. 22 inches; operating in normal forward orientation is:

Velocity on road =   ×

   

Apart from this, for mounting the engine we are going to use neoprene rubber mountings.

For the normal orientation of the transmission system and maximum speed of the vehicle as 60 km/hr radius comes out to be 11 inches. Apart from outer radius of the tire, other factors for the selection of tires include tread width, tread design, side wall width, load handling capacity, number of plies and treads on side wall etc which define the traction ability, tire resistance to wear and puncture and performance of the tire on various terrains.

3.3 TIRES

Reason:

Selecting the tires is one of the most important things as the whole vehicle is in contact with the road on these 4 points or rather patches. Also for designing an all terrain vehicle tires form the most important part. They should be such that they are able to provide enough traction on all kind of surfaces so as to transmit the torque available at the wheels without causing slipping.

1. Built with a 6 ply rating and a reinforced casing makes these one of the most puncture resistant tires in the market today.

Front

3. The deep tread and open wing design provides excellent clean-out with each lug and an improved traction.

First Second Third Forth Reverse

- 10 to 12 km/hr - 15 to 18 km/hr - 25 to 33 km/hr - 40 to 51 km/hr - 8 to 11 km/hr

2. Large shoulder knobs wrap down the sidewall to provide excellent side to pull out of the ruts without causing sidewall failure.

4. Special natural compound delivers added traction. 5. Smaller tires in front results in a smaller magnitude of moment on the wishbones due to cornering forces during steering. Outer diameter of tire – 21 inch Outer diameter of rim – 10 inch Tread width – 6 inch Aspect ratio – 0.68 Number of plies – 6

Rear

Outer diameter of tire – 22 inch Outer diameter of rim – 10 inch Tread width – 8 inch

6. Use of the larger outer diameter tire at the rear helps to provide good ground clearance and also 8 inch treads provides good traction to the power wheels.

3.4 BRAKES 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. For designing the braking system this year, we calculated the weight of our vehicle in static condition as well as in dynamic condition as per the deceleration (0.6 g) and stopping distance. In static condition it is around 60kg on each front tire and 110kg each on the rear tire. But in dynamic conditions, we consider weight to be 85kg on each tire, the front and the rear. We have calculated the dynamic weight using the formulae as given below:





g = Acceleration due to gravity. W= Total weight of the vehicle. H=Height of center of the gravity. L= Length of the wheel base. Deceleration of the vehicle is α.

The above highlighted specifications have been selected for our vehicle. We selected these as per our design of the braking system for 5.9 m/s^2 deceleration.

3.5 STEERING SYSTEM

We planned to use disc brake in all four wheels. Initially we thought of using disc brake in front and drum brakes in rear but problem with drum brake is of locking .For achieving the condition for locking at once on the application of brake paddle, it is preferred to use disc in all four wheels. Some formulas that we used for designing our brakes:

T (disc) = 1 ×

 

×

1 + 2 ×

 

× 2

T (disc) =  ×  ×  ×  × 2 × .    Where, T (disc) = Frictional torque on the disc f = deceleration W = weight of the body R = Effective radius of disc R1= Radius of front tire R2= Radius of rear tire P = Pressure applied by the TMC. µ= Coefficient of friction R=Radius of the disc A= Area of the caliper for disc brake P= Pressure applied by the master cylinder. Using these formulae, we have done our calculation and selected our brakes. Some of calculations are shown in the table 5:

After a comparative study on different steering which are available in the market it was found that the best suitable steering for our vehicle is central roller and rack. Table 6 shows results of our study on steering. Table 6: Steering comparison Types of steering

Rack and pinion Central roller and rack

cost

low

low

weight

Sensitivity and response

efficiency

light

poor

fine

light

good

good

Recirculating ball type

high

m edium

poor

Very good

Worm and roller

medium

heavy

poor

medium

Worm and sector

medium

heavy

Very poor

good

Table 5: Brake pedal force calculation F

Pr

kg

D1

D2

R

R1

R2

mm

mm

inch

inch

inch

3.0

3.21

16.25

16

98

10.5

11

2.5

3.86

16.25

16

98

10.5

11

3.0

3.84

17.78

16

98

10.5

11

3.8

3

17.78

16

98

10.5

11

3.2

3.58

17.78

16

98

10.5

11

3.0

4.44

19.05

16

98

10.5

11

3.2

3

16.25

16

98

10.5

11

• Central roller and rack. • Turning radius – 8 feet. • No. of teeth on the Rack bar =36 • Length of rack = 144mm • The ratio of the rack and pinion = 12:1 • The axial pitch of the Rack bar = 6 mm • Steering ratio –7.8:1 • No. of universal joints in column = 2 • Column inclination from horizontal- 45 degree • Removable steering wheel assembly for the ease of driver exit in time specified as per the rulebook. • No. of the tie rods = 2.

Figure 4: Central roller and rack Where the parameters shown above are as under:







Apart from deciding the steering ratio we have not been able to design the linkages, tie rods etc as presently we do not have the gear box of steering.

*Double wishbones are usually considered to have superior dynamic characteristics, load handling capability and are still found on higher performance vehicles.

The formulae used for steering calculations are: 



=





+





 =  +  +      −     

Spring Design started with some arbitrary parameters within the constraints Constraints: Weight, ground clearance required and space limitations

 =  +      − 

Where, C – Length of tie rod X, Y – lengths as shown in fig 5 p, q – angles as shown in fig 5 a – length of steering knuckle from center of tire b – Perpendicular distance of steering knuckle from pivot point as shown in fig 5. FIGURE 5: Steering knuckle

Estimated weight of vehicle

250 kg approx.

Driver with accessories

90 kg approx.

Total weight with driver

340 kg approx.

Unsprung mass

75 kg approx.

Sprung mass

265 kg (at max. with driver)

Now according to design for rear wheel drive drive 40% of the total weight will be distributed at the front portion and the remaining 60% of the weight will be at the back or rear end.

3.6 SUSPENSIONS Suspension is the term given to the system of springs, shock absorbers and linkages that connects a vehicle to its wheels. The suspension systems not only help in the proper functioning of the car's handling and braking, but

From the above estimated weight we find that weight distribution at one side of front end will be approximately 70 kg and at one side of rear end will be approximately 105 kg. So, all the calculations will be done taking this weight distribution only.

3.6.1

FRONT SUSPENSIONS

The spring damper would be placed at the centre of the





Table 7: Front suspension spring details

Table 8: Rear suspension spring details

Length of spring

171 mm

Length of spring

230 mm

Total length(spring + damper)

291mm

Total length(spring + damper)

490mm

Wire diameter

7mm

Wire diameter

11mm

Mean coil diameter

51mm

Mean coil diameter

80mm

Allowed travel of spring

100mm

Allowed travel of spring

72mm

Stiffness

20N/mm

Stiffness

30N/mm

Pitch

19mm

Pitch

19mm

No. of active turns

10

No. of active turns

10

Total no. of turns

12

Total no. of turns

12

Initial compression (after driver is seated) = 33.3mm

3.6.2

REAR SUSPENSION

Here also the constraints were ground clearance 8 inches, vehicle weight 110 kg on each tire and movement of transmission shaft as shown in figure 7; full angle being 15 degree, full jounce 3 degree and full rebound 12 degree

From initial compression we conclude movement of shaft required is 6.3 degrees

3.6.3

that

DESIGN AND ANALYSIS OF WISH BONES

FRONT SUSPENSION

In here, we keep the mounting point of the spring on the upper wishbone and at its end. The rear suspension system is as shown in figure 7. Figure 7: Rear suspension on optimum k

REAR SUSPENSION

the





TABLE 9: Hub weight comparison Hub assembly weight of 3kg and 440gms 2010 Hub assembly weight of 14kgs and 780gms 2009 Hub assembly weight of 22kgs and 340gms 2007 FIGURE 8: Hub design on pro-e

7.0 CONTACT Vikrant Dalal Mechanical Engineering student Institute of Technology and Management, Gurgaon Web site – www.thetechietyros.com Email I.D. – [email protected] Address: V.P.O Goela Khurd, Najafgarh New Delhi 110071

4.0 CONCLUSION As discussed earlier, our approach is to design for the worst and still optimize so that we avoid over designing. This would help us to reduce the cost. The approach that we followed is iterative in nature and processes like reverse engineering are adopted in order to select various systems from the ones, existing in the market. This step would ensure standardization and reliability would follow as a by part. Our top priority would always be the safety of the driver and working in this direction, we will strive to add aesthetic value and a sense of ergonomics to the vehicle.

5.0 ACKNOWLEDGMENTS The design process is not a single handed effort and so it is my team, whom I wanted to thank for standing with me under all circumstances. I would also like to express my gratitude towards our Mechanical department and on the whole towards the college for supporting us and

engine Type Displacement Compression Ratio Power Torque Drive Train Transmission

Company Chassis/Suspension Chassis Type Overall Length Wheel Base Overall Width Front Suspension Rear Suspension Ground Clearance Shocks Front Travel Rear Travel

4-stroke, gasoline Lombardini engine 305 cc 8:1 8 KW 19 NM at 3000 rpm 4 speed manual constant mesh gear box with 1 reverse Mahindra alpha champion IS 1239 Steel Pipes 1400 mm. 1150 mm. 1600 mm. Double Wishbone Double Wishbone 250 mm coil-over 200 mm. (75 mm rebound and 125 mm jounce ) 100 (75 rebound

design reportof baja sae india -2010

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