Design Report2

R V College Of Engineering

Bangalore

Project Garuda 2011 Design Report

Project Garuda 2011

1.Mission Statement:

The overall goal of this project is to design and fabricate a single-person, fuel efficient vehicle powered by a modified, iso-octane burning Honda four-cycle 2.1 hp motor. The objective of the Supermileage Team is to apply our engineering knowledge and experience to design and build a vehicle that will achieve in excess of 1000 miles per gallon while satisfying all of the Shell Eco Marathon Competition rules and requirements. This target will be met by designing and constructing a lightweight, aerodynamic shell that will house a modified Honda 50cc engine.

2.Introduction:

RVCE Supermileage team consists of student from various engineering backgrounds working on a common objective of building a highly fuel efficient vehicle making this project truly interdisciplinary. Over the last few months the project has made significant progress and is now currently working on the 2011 prototype to take part in the Shell Eco Marathon Event.

2.1.Our Aims and Targets:

Build on existing platform and optimize the Design efficienciesTarget to obtain a mileage of more than 1000mpg Use the Supermileage energy efficient platform, to test out alternate energy options and optimize automobile energy requirements To improvise existing design and develop expertise in the field of 1) Automobile Design and Manufacturing2) Computational Fluid Dynamics (CFD)3) Engine Design4) Electronic Fuel Injection (EFI) Systems

The main intent of this project however, is to collaborate with various minds across the industry and build on technical knowhow.

R V College of EngineeringDept of Mechanical Engineering

Project Garuda 2011

3.Vehicle Configurations:

Our vehicle is a single seater and has three wheels. The driver sits in a reclined position with his/her legs directed towards the front of the vehicle.The two independent wheels are mounted on the front and the drive is sent to the rear wheel.The Engine, transmission and its associated components are mounted in the rear section of the vehicle, that is, just behind the firewall and the roll-cage. The steering system controlling the front two wheels is based on the Ackermann Steering System, taken from a go-kart.Our Chassis is made of tubular aluminum and the shell is made out of Fiber Reinforced Plastic, a patented plastic generously donated by General Electric (GE).Overall length of the car is 2400mm, maximum width being 600mm and maximum height above the ground being 700 mm. the minimum ground clearance is 100mm.


Project Garuda 2011

VEHICLE SYSTEMS:

4.Engine :

The engine of the Shell Eco-Marathon car is power source for the vehicle, converting chemical energy stored in the fuel to rotational mechanical energy output by the driveshaft. Three different base engines were considered for the Eco Marathon vehicle including: a modified SAE Briggs and Stratton engine, a Honda GX35 used by the 2010 Eco-Marathon team, and a Honda GX50.

4.1. SAE Briggs and Stratton:

Teams entering the society of Automobile Engineers (SAE) Supermileage competition are required to use a 148cc Briggs and Stratton engine as the basis of their design.Garuda team in the past have experimented with this engine and made progressive modifications to the base engine including converting a side head valve engine to over head valve engine and reducing the displacement by altering the bore and stroke. The engine has not run for several years and is less efficient than some of the stock engines because its design is not optimized to run at the lower displacement it has been modified to. We are not planning to compete at the SAE Supermileage, therefore the use of Briggs and Stratton engine will not be required. Using a small displacement base engine will have the advantage of a more optimized design and a significant weight reduction over the Briggs and Stratton engine, giving us an advantage over teams planning to compete at the SAE event.

4.2. Honda GX35:

The 2010 RVCE Supermileage team used a 35cc Honda engine.The Honda engine is small and light but produces its maximum power and torque at high engine speeds where fuel consumption is also high. As well, the vehicle as currently designed has been


Project Garuda 2011

proven underpowered for initial acceleration, partly due to the insufficient torque available from the engine. Further the engine is designed for use with carburetor and would require significant modifications to convert to a fuel injection system. These limitations warranted research into stock fuel injected engines suitable for the application and the decision to pursue a new base engine for the 2011 Eco-Marathon vehicle.

4.3.Bajaj Kristal Engine: The 95cc Bajaj Kristal engine is designed for fuel economy and comes with a stock auto clutch system. The engine is compact and light weight, while incorporating many of the advanced technologies used on larger displacement engines. We plan to incorporate an electronic fuel injection system to this engine to have greater control over the air to fuel ratio. With these few additions the Bajaj Kristal engine should provide an excellent base engine for our design and for future Eco-Marathon teams to improve on. Based on the discussion presented above the Bajaj Kristal engine was selected as the base engine for the 2011 Eco-Marathon vehicle.

Bajaj Kristal Engine5. Fuel System:

The fuel system is responsible for supplying the correct air/fuel mixture to the engine for combustion, balancing power output and fuel consumption. Our design requirements specifically state that the 2011 Shell Eco-Marathon car will use a fuel injection system (for improved fuel delivery), so a carbureted system was not considered as an option. As well, Shell does not permit the use of electric fuel pumps for the Eco-Marathon competition. The remaining two options were: manifold injection with a mechanical fuel pump and throttle body injection with pressurized fuel.

5.1. Direct Injection (MI) with a Mechanical Fuel Pump:

Direct Injection is the most efficient form of fuel injection where high pressure fuel is delivered to the cylinder during compression stroke (figure 3). A mechanical fuel pump, driven by the engine’s crankshaft, would provide the power to pressurize fuel. Direct Injection offers precise control of fuel metering and excellent fuel distribution to the


Project Garuda 2011

engine. As well, direct injection requires precise control of injection timing and is uncommon in small engines.

5.2. Throttle Body Injection with a Pressurized Fuel System:

Throttle body injection delivers fuel to intake air instead of directly into the cylinder. Throttle body injection requires lower fuel pressures than direct injection systems because the injection point is at lower pressure. As a result, it is possible to pressurize the fuel with a compressed gas and eliminate the need for a mechanical fuel pump, requiring no energy from the engine. Throttle body injection offers comparable fuel metering precision to direct injection and also requires less precise injection timing. Based on these advantages, throttle body injection was selected for 2011 Eco-Marathon vehicle.


Project Garuda 2011

6. Electronic Control Unit (ECU) and Sensors:

Having the EFI (Electronic Fuel Injection) system gives a computer controlled injection rather than a mechanically controlled one. The ECU (Engine Control Unit) is incorporated and is designed as an embedded microcontroller system with inputs and outputs connected to the ADCs (Analog to Digital Converters) and DACs (Digital to Analog Converters) respectively.

The reasons for using an ECU instead of the traditional carburetor system are as follows:1. Highly Accurate Air/Fuel Ratio Control Throughout all Engine Operating Conditions.2. Atomization of fuel occurs due to the injectors, creating better mixing of air and fuel.3. eliminates the head losses (pump losses) through the venture of the carburetor.4. And most importantly, Electronic Fuel Injection (EFI) is considered to be superior to carburetion because it allows more precise fuel metering for easier starting, lower emissions, better fuel economy, and performance.

In addition, the EMS controls other subsidiary functions, which are as follows:

1) The spark timing, discussed in the section on the ignition system.2) Limiting the speed to which the engine can rev.


Fig: Throttle Body Injection

Project Garuda 2011

The layout of the EMS used in ‘Garuda’ is shown below:

The Engine Management for our car is carried out by a simple and easy-to-install ECU system. The RD0601 ready to use ECU kit implements the above functions. The RD0601 is essentially a 32 bit, RISC (Reduced Instruction Set Computer) microprocessor.A generic block diagram of our Engine Management System is shown below:

Sensors used include a Throttle Position Sensor (TPS), a Camshaft Position Sensor and a Temperature Sensor. Details of each sensor used are given below:

6.1. Throttle Position Sensor:A DELPHI throttle position sensor (Essentially a Hall Effect sensor) hasBeen attached to a mechanical throttle Body as shown in the picture.

Advantages of using this sensor:

*Non-contact sensor provides increasedDurability and reliability compared To contact sensor designs.*Contact sensor is physically separated From the gearbox to avoid gear dust Contamination of sensor and reduce shaftPosition variation for improved warranty performance

6.2. Camshaft Position Sensor:A Suzuki Camshaft Position Sensor (a HallEffect sensor) is being used by us for accurateDetection of the camshaft position.Specifications:


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a. RPM Range: 10 to 36000 RPMb. Output Voltage: 0.4V dc max.

6.3. Temperature Sensor:A DELPHI temperature sensor is used in ourEngine to measure temperature variations while Engine runs. Mode of operation of such sensors is a change in resistance of a thermistor insidethe sensor with variations in temperature.This relation is inversely proportional in nature.

Specifications include:Thermal and Electrical Properties

Typical voltage supply: 5 V DC Operating temperature: -40°C to +135°C Resistance at 25°C: 2795 ohms Thermal time constant: 60 seconds in dry air stream Accuracy (±°C) -40°C to +100°C: 0.56 to 0.77 Accuracy (±°C) +100°C to +150°C: 0.77 to 1.24

A single actuator is being used presently, that being the fuel injector:A DELPHI fuel injector is used for our purpose as itSatisfies our requirements for spray pattern, linear range, working flow range and operating voltage.

Specifications include:

*Injector quality performance...<1ppm*IPTV at 12 months (4-cylinder applications)...<.7*Plugging test cycles with <5% flow shift...>300 (Delphi test cycles)*Dynamic durability, % at billion (1,000 million) cycles...+/-3%*Tip leakage (mean cc/min) air at 420 kPa...<0.02 cc/min*Spray SMD, m at 400 kPa, 3.0 g/s...<50 mμ μ*Linear range with 5 V minimum...>16*Minimum operating voltage at 400 kPa...<5.0 V

Picture shows the Multi Point Fuel Injection (MPFI)


Project Garuda 2011

Injector being used in our car. MPFI ensures better quality of fuel injection and hence a complete optimized usage of fuel.

6.4.ECU MAPPING:

The RD0601 EMS system being used in our car utilizes a visual basic (VB) software interface And hence provides us with the facility of fuel injection and ignition timing control.

We use a 20*16 tuning map for fuel and ignition and a 10*1 tuning table for injection opening time and ignition dwell based on battery voltage.

An added accessory is a 10*1 tuning map for fuel and ignition correction based on the following factors :*) Air temperature.*) Engine temperature.*) Battery voltage.*) Altitude. A rev limiter and a VTEC (Variable valve Timing and lift Electronic Control).

The ecu maps are lockable and the injection sequence can be programmed for fully sequential, semi-sequential or of batched operation.

A 20*16 map allows us to specify the injector nozzle open time for a wide range of RPMS at particular engine load value. Real time mode of operation shows us enigne rpm, temperature, air to fuel ratio in real time. We then set the injector open time values in the map and 'Send to the ECU'. 'Burn to ECU' stores the map values permanently in the ECU RAM.

The typical 20*16 injection map used by us is shown above.

All signals from sensors are fed to the microprocessor chip through a simple data bus system. A serial bus / Bafo (a serial to USB adapter) system connects the ECU system to our computers. The microprocessor board runs on the same 12V battery source (1.4 Ah) being used for all other systems onboard the car. Detailed studies on the ignition


Project Garuda 2011

curves and rpm v/s load curves gives us an idea about the optimum fuel amount to be injected at the rpm level range at which our car will run. The RD0601 ecu system has proven itself robust, reliable and easy to use. Using the RD0601 we can display up to four of the available ECU parameters and have the values updated in real-time as we drive. It also decodes the internal ECU error codes as they occur and displays them in real time. Having the EFI (Electronic Fuel Injection) system gives a computer controlled injection rather than a mechanically controlled one. Electronic fuel injection is considered to be superior to carburetion because it allows more precise fuel metering for easier starting, lower emissions, better fuel economy and performance.

7.Drive mechanism:

The drive mechanism transfers the power generated by the engine to the clutch, transmission and finally the rear wheel to propel the vehicle. Three concepts for the drive mechanism were considered: belt drive, gear drive and chain drive.

7.1.Belt Drive:

Belt drive systems use pulleys that grip the belt on either end while they rotate transmitting the angular rotation of the input pulley to that of the output pulley Friction belts, such as flat or v-belts, are unstable because of inherent power loss when slippage occurs as high torque overcomes the friction generated by the tension in the belt. A notched synchronized belt is more efficient because it uses grooves cut into the belt, low in cost, and do not require lubrication; however a belt drive is not as robust as a chain or gear drive because belts tend to wear and stretch with extended use. As well, synchronized belts are not compatible with belt drive transmissions (such as variable diameter sheaves); therefore a secondary drive mechanism would be required if a belt drive is used .The disadvantages of a synchronized belt drive outweigh the benefits, eliminates it as an option.

7.2.Gear Drive:

In a gear drive, power is transmitted through the teeth of meshing spur or helical gears. A gear drive is efficient and has low maintenance, but weighs significantly more than a belt drive or chain drive and is more costly. As well, a gear drive is not practical for transmitting power over distances that require idler gears to connect the driven and driving gears because of the increased weight of the additional components. The layout of the Eco-Marathon car’s power train will require a distance between the engines and drive wheel that would make a gear drive impractical, thus a gear drive impractical, thus a gear drive is also unsuitable.

7.3.Roller Chain Drive:

The idea of a roller chain drive is much the same as a synchronized belt system in that both the drive and driven pulleys or sprocket have teeth that grip the notched roller


Project Garuda 2011

chain as they rotate, transmitting power. Roller chains are durable and offer high transmission efficiency at a reasonable cost compared to a belt or gear drive.

8.Clutch :

A clutch is necessary to engage and disengage the engine to control movement. As well, a clutch to disengage the engine while starting is a requirement for the Shell Eco-Marathon. Three different clutch designs were designs were considered: centrifugal clutch and cone clutch.

8.1. Centrifugal clutch:

A centrifugal clutch (Figure 4) uses the angular velocity of the engine’s driveshaft toExtend a rotating mass, creating pressure between two friction surfaces to transmitPower to an output shaft. At low engine speed, the clutch is disengaged because theCentrifugal force is not large enough to cause the rotating mass to move the frictionPlate outward and lock onto the output mechanism. However, as the engine speedIncreases the centrifugal force generated by the rotating mass pushes the frictionPlate to the outer drum, allowing power to be transmitted. Centrifugal clutches allowThe motor to develop high torque before engaging and operate at high efficienciesonce engaged. Thus the centrifugal clutch is suitable for the Eco-Marathon vehicle.

Figure 4: Centrifugal Clutch

8.2. Cone Clutch:

Friction cone clutches offer superior transmission of high torque because the designprovides a wedging action that helps the frictional surfaces to bond together (Figure5). As a result of the wedging action, more force is required to disengage the clutchcompared to a plate clutch. A cone clutch was eliminated because of its additionalsize, weight, and design complexity compared to a plate clutch described below.


Project Garuda 2011

Figure 5: Cone Clutch

9. TRANSMISSION:

A transmission is required to provide a variety of gear ratios to optimize fuelefficiency throughout the range of operating speeds encountered during the course ofthe competition circuit. Three transmission designs were considered: continuouslyvariable, planetary hub, and sprocket and chain.

9.1. Continuously Variable Transmission (CVT):

A CVT transmission (Figure 6) uses a mechanism to open and close both the inputand output pulleys, changing the input to output gear ratio. A CVT transmissionoffers a large range of gear ratios and smooth shifting between gears. As well, a CVTcan be designed to disengage at low speed, eliminating the need for a separate clutchmechanism. The major drawback of a CVT is inherently lower efficiency due to beltslippage and the weight of all the required components (sheaves, clutch arms andweights, springs, etc.). These disadvantages eliminated the CVT as an option for theEco-Marathon transmission.


Project Garuda 2011

Figure 6: Continuously Variable Transmission

9.2. Planetary Hub Transmission:

A planetary hub transmission (Figure 7) uses a series of planetary gear sets enclosedin a bicycle wheel hub to offer a range of gear ratios. This design is compact andrequires low maintenance. The drawbacks of a planetary hub transmission are itshigher cost and weight compared to a simple chain derailleur system, as well as itslack of availability at power ratings required for the engine of the Eco-Marathonvehicle. Planetary hub transmissions are typically designed for bicyclists and are notable to take the higher torque and speed of a gasoline engine, therefore hubtransmission is unsuitable for the Eco-Marathon vehicle.

Figure 7: Hub Transmission

9.3. Direct Transmission:

A sprocket and chain transmission (Figure 8) similar tothat of a bicycle to move a roller chain from a large sprocket to a smaller sprocket, effectively increasing the output-to-input gear ratio of the transmission. The largergear would be used to provide the high torque needed to accelerate the vehicle fromthe starting line, while a smaller gear(s) would be used to provide acceleration to topspeed. Advantages of a sprocket and chain transmission are its light weight,high efficiency, and low cost. A disadvantage of the sprocket and chaintransmission is its limited gear ratios compared to a CVT or planetary hub. Overall,the sprocket and chain is the best alternative for the Eco-Marathon vehicle’stransmission.


Project Garuda 2011

(fig 8:Direct Drive)

10. Final Design

The final design selection is based on an assembly made up of the five componentsdiscussed above. Table 1 summarizes the alternative chosen for each of the fivecomponents. Each of the components and its design will be discussed in more detailin the following section. Table 1: Components Selected for Final Design

Component SelectedEngine Honda GXH50Fuel System TBI with Pressurised Fuel SystemDrive Mechanism Roller chainClutch Centrifugal clutch

10.1.Engineering Design:

Intermidiate drive:


Project Garuda 2011

A direct chain drive from the engine to the wheel sprocket will be incorporated. An automatic clutch assembly will be used to increase efficiency.

The Honda GXH 50 cc engine comes with a power of 2.1 bhp (@7000rpm) and a max torque of 2.8Nm (@4000rpm).

10.2. Calculations:

1. Sepang circuit distance (single lap) =2.8km only 30% of this distance is done by running the engine=0.84km

2. Number of laps to be done=4

3. Max time=28min (for 4 laps)=7min/lap30% of this value=2.1min/lap=0.035hr/lap


Project Garuda 2011

4. V= dist/time 0.84*1000 = 6.67m/s 0.035

5. V=W*r 6.67=W*0.127 (W)wheel=52.51rad/sec Speed of wheel=60*33.35 = 501.46rpm 2*3.142

6. Speed of engine=4000rpm (W)engine=2*3.142*4000 = 418.93rad/sec 60

7. (W)wheel = no. of teeth on engine shaft (W)engine no. of teeth on wheel sprocketAssuming no. of teeth on engine shaft=12 418.93 = 12 teeth no. of teeth on wheel sprocket

No. of teeth on wheel sprocket=100

8. Gear reduction=96/12=8

Intermediate Drive:

An intermediate drive will be included to change the direction of rotation and also to change reduction since we need a reduction of 1:20.

So the number of teeth on the intermediate drive will be 48 and 20.

Acceleration:

1. T/r = F 2.8/0.0075 = 373N

2. F/20 = (F)wheel 373/20 = 18.65N

3. (F)wheel+mmg = ma 18.65+0.3*9.81*100 = 100*a a=3.1295m/s

4. For 45kmph, v = u+at


Project Garuda 2011

45*10^3 = 0+3.1295t 3600

t=4 sec

For 65kmph, t=5.32sec

11. CHASSIS:

The material selected for construction of the chassis is aluminum 6063, T6 age hardened. This was our material of choice because of its relatively high specific strength for its weight, ease of machinability and its corrosion resistance. We specifically chose 6063, T6 grade due to its availability in Bangalore and due to its widespread use in structural applications.

Wheel base: 78 inchesWheel Track: 18 inchesMaximum height: 11 inchesGround Clearance: 6 inchesChassis Material: Tubular Aluminum, 6063, T6.

Tubular cross-sections employed: Square cross-section 1’’ X 2” and circular cross-section of 1” diameter. Rectangular cross-sections were preferred over Circular ones because they have a higher Moment of Inertia (MI) and hence are stronger.

Tubing Specifications: Al 6063, T6 properties: Density: 2700 kg/m^3Elastic Modulus: 70 - 80 GPATensile Strength: 310 MpaYield Strength: 275 Mpa

Tubing Dimensions:Circular Tubing:

Outer Diameter: 1 inchTubing Thickness: 2.54mm

Rectangular Tubing:External Dimensions: 1 inch X 2 inchTubing Thickness: 2.54mm

11.1.Chassis Design Methodology: The Shell Eco-Marathon Chassis components undergo a variety of loads during operation. To assess the strength of chassis under different loading conditions, we have used Inventor to validate our designs.


Project Garuda 2011

The various loads considered during the design of the chassis were:A 75 kg load on the roll cage with varying force components.Driver weight along with vehicle components.Road reactions at the location where running gear is mounted.Vibrations due to reciprocating parts in the engine.Gyroscopic forces associated with the drive train.Dynamic forces during turning, braking and acceleration.

The priorities taken into account while designing the chassis are:To provide safety to by suitably designing the roll cage to protect the driver in case of a rollover.Ensuring that the chassis remains stable and copes with the dynamic forces involved during operation. To minimize weight and to optimize the space frame to accommodate the necessary components that constitutes the other systems.

The driver position was selected as semi-reclining to strike a balance between good visibility and an aerodynamic shape. The weight distribution in the chassis had to be managed so that, after mounting the engine components, the drive train, the engine accessories and the safety equipment, the weight balance is acceptable.

To achieve the above goal we made use of two different cross sections of tubing, circular cross-section tubing in reinforcing members and the roll cage and rectangular cross-section tubing in the load bearing members. This greatly improved not only the weight distribution but even the rigidity of the chassis.

The chassis was designed based on the previous design was optimised for weight reduction.the chassis now weighs 3 kgs lesser than the previous design.

The application of load on the chassis.The driver’s weight and engine’s weight are the major weight considerations.


Project Garuda 2011

The ladder frame provides more rigidity and provides a more stiffer platform for the application of loads.Now the frame is being analysed for stress:


Project Garuda 2011

According to the rules the roll hoop must be able to withstand 70kgf of load.


Project Garuda 2011

The roll hoop is required to protect the car during an accident when the car overturns. Here the roll hoop is analysed to withstand 70kgf.the roll hoop consist of 1” circular section profile over a path to protect the driver.

12. The Steering System:

This section will deal with the selection, design, and fabrication of the steering system to be implemented in our ecomarathon vehicle, keeping in mind the various constraints imposed by the competition rules as well as the economics of our project.

12.1 Classification of Steering Methods:


Project Garuda 2011

The very first decision to be made was whether to select a front wheel steering or a real wheel system. Since our vehicle would have only three wheels, two in the front and one at the rear (the rear wheel being the drive wheel), it was possible to incorporate either front wheel or rear wheel steering. Front Wheel Steering:One of the benefits of using this method of steering is that it provides a staple steering system. In a three wheeled vehicle with a single rear wheel such as our Supermileage vehicle it is also advantageous in the respect that only the single rear wheel is effected by frictional scrub. This system ensures better road grip and reduced tire wear. There are some disadvantages of the front wheel steering system as well. Having room in the front of the vehicle for the two wheels to swivel requires a larger frontal area, which corresponds to larger aerodynamic drag.Rear Wheel Steering:A major benefit is the simplistic design when only one wheel turns. With the two front wheels stationary they can be brought in closer to the driver’s legs to decrease the frontal area and corresponding aerodynamic drag. A major disadvantage of steering the rear wheel is that two wheels become stationary and suffer from scrub losses. After a comparative study of the two methods, it was decided to incorporate a front wheel steering. The front wheel system would be easier to control for the driver. Hence it was decided to design and fabricate a front wheel steering system for our vehicle.We decided to go with the simple go kart geometry of steering.


Project Garuda 2011

12.2. Working of Ackermann Steering:In the above sketch, PC and QD represents the stub axles of each wheel. PA and QB represent the steering/pitman arms, and AB the track rod. The angle represnts the αAckermann angle.Also it may be noted that the dotted lines intersect at a point between the front and rear axles approximately 0.3L in front of the rear axle, where ‘L’ is the wheel base.Hence our first step will be calculation of the Ackermann angle ‘ ’.α

Ackermann Angle ( ):αThe very first data required for this calculation is the wheel base and wheel track.the wheel base was determined taking into account the driver’s measurements in the seated position, space for the engine and gearbox, as well as mounting of the rear wheel. After numerous iterations a wheel base of 1700 mm was obtained. the wheel track was determined once again keeping in mind the driver’s overall width and adequate space for the steering system. However the main criteria was tolerance between the shell and the wheel in its fully turned position. Taking all this into account we arrived at a wheel track of 600mm from centre to centre of each kingpin.Next a triangle was constructed from the above sketch of the system. This is shown below. In the figure alongside, Wheel track PQ = 600 mmWheel base L = 1700 mmHence DE = 600/2 = 300 mmCD = L -0.3L = 1190 mmHence tan = 300/1190α

Or Ackermann angle = 14.14 α≈ 15 degrees


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Turning Radius:


Project Garuda 2011

Outer radius =120.81 cmInner radius=56.07 cm

12.3. Kingpin Inclination (Steering Axis Inclination):

The inclination (usually an inward tilt) of the kingpin from the vertical is called the kingpin inclination, or kingpin rake. The kingpin is the main pivot in the steering mechanism. It is also a load bearing structure since all loads acting on the vehicle are taken up by the kingpin thereby preventing any stress on the steering system. The kingpin inclination helps in steering return ability, i.e. straight ahead recovery, thus providing directional stability.


Project Garuda 2011


Project Garuda 2011

12.4. Camber Angle:

Camber is the tilt of the wheels from the vertical. Camber is positive if the wheels tilt outward at the top. Camber is also called wheel rake.

It is always desirable that the tires should roll on the ground vertically so that the wear is uniform. If while running, the wheels are inclined either outwards or inwards, there will be more wear on one side than the other. Hence it is ideal to maintain a zero camber.In order to do this the wheels are initially given a slight positive camber, in the unloaded condition. Thus when the driver sits inside the vehicle, or when the vehicle is loaded, the positive cambered wheels will now achieve zero camber.For an overall weight of 100 kgs(driver and components),the deflection produced was very minute. Therefore small positive camber of 5 degrees.

12.5.Fabrication:Aluminum sections will be used to build the steering sections.Circular sections of 1 inch diameter and 2mm thickness will be fabricated to make the steering system for our vehicle.Tie rods will be 25 cm in length.


Project Garuda 2011

Bearings will be used at each joint to reduce friction between the moving parts.

13. SHELL:

The shell design and fabrication represents one of the most complex and challenging aspects of our project.

13.1. Shell Design Considerations:1) The shell geometry should have as low a drag co-efficient as possible, thereby Reducing air resistance and improving mileage.2) The Aero design must produce as low negative lift (down force) as possible.3) The shell should be light weight.4) It should be possible to mount the shell to the chassis.5) Parts of the shell should be readily detachable to facilitate driver exit as well as Servicing of vehicle components.6) The shell surface should be as smooth as possible, so as to reduce friction drag.7) The finalized shape should be easy to fabricate.

The drag force experienced by the shell can be divided into two components, namely form drag and the frictional drag. Our goal is to determine the optimal shell design to reduce both components.

The basic design factors that reduce the form drag are:1) Reducing the frontal area of shell2) Contouring of shell to provide optimal streamlining3) Prevention of separation of flow, both through optimal contouring and using special Techniques for boundary layer control

The friction drag is influenced by the surface roughness of the body, as well as the surface area (particularly over which un-separated flow occurs).Further, to reduce the negative lift experienced by the shell, we need to reduce the upsweep at the rear of the shell as far as possible, preventing the formation of a large low pressure region at the rear underside of the shell that would reduce down force at the rear.In order to design a contour that was relatively simple to analyze and fabricate, we needed to settle upon a basic curve/function to define the various contouring of our shell. In order to do so, we made many designs in Pro-E and then short listed a few based on the simplicity of design and aerodynamic profiles. This results in a shape similar to a symmetric airfoil, when viewed from the top.

13.2. Positioning of Vents:Another important consideration in our shell design is the positioning of air-vents for the intake of air for combustion and cooling of the engine. We hence located our air vents at the front of the shell, near the nose. The reason for this is that the stagnation points of flow are located in this area, contributing the maximum to form drag and generating a high positive pressure gradient. Hence, by placing our vents here, our


Project Garuda 2011

vehicle literally funnels the air into the engine as it moves forward. The air is carried to the engine at the rear via tubing. The drawback of this system is the high engine pump work when the vehicle is stationary; however this will rarely be the case during our performance run, and so will not hurt our mileage score in the competition.

13.3. Provision to cover the wheels:If the shell is to cover the wheels, sufficient room must be left for the front wheels to turn during steering. While the vehicle is in motion, there is continuous movement of air around it. If the wheels are not covered, the air, by deviating from its laminar flow, moves across the spokes of the wheel thereby obstructing its proper motion. This is similar to the egg beater effect where this kind of movement of air causes resistance to the rotation of the wheels and hence resists the vehicle movement. To prevent such inefficiency, we decided to keep the wheels covered inside the shell, keeping in mind the provision for the turning of the wheels while steering.

13.4. Shell Material and Fabrication:The main factors that decided the selection the selection of the shell material wereLightweight and robustness.The ease with which it can be fabricated (flexibility).Availability of the material locally.Cost of the material.

13.5. Shell Material:

The shell will be made using Glass fibre and Polyvinyl Ester as this material is very light .

13.6 .Shell Models:

From paper to CAD:


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This image shows the vehicle configuration with two wheels in the front and one wheel at the rear.

14. Wheels and Brakes:

The requirements for our wheels and tires are as follows:

1. Sufficient Mechanical Strength, especially considering cornering forces.2. Light weight.3. Low air-resistance, especially for the front wheels, as they are exposed to the air stream4. Low rolling resistance.

Wheel and tire dimensions: The dimensions of our wheels settled upon are as follows:

Front Wheels: 17 inch, locally available wheels, as smaller sized wheels improve handling, and cornering stability. In addition to this, small tires also provide less air resistance. Smaller the tires, lower is the car and hence better are its aerodynamics. However a smaller tire requires more number of rotations to cover the same linear distance as that of a bigger wheel. Hence, optimization is required. The 17” tires will be used for road testing purposes.

Rear Wheels: A 20 inch wheel, with a racing slick tire is used in the rear as large size wheels at the rear improve traction, and also provide better grip at the rear during braking. Further, lesser rotation of a bigger wheel covers a larger linear distance as compared to a smaller wheel.Based on these criteria, we will be purchasing our wheels and tires from Schwalbe North America, as they have the correct tire specs and tire dimensions to suit our purpose.Wheel Selected: Stelvio HS 350, Folding Bead tires.


Project Garuda 2011

14.1. The Hub:Dimensions :

The hub will have a diameter of 25mm The spoke housing will have a diameter of 35mm The distance between them will be 1mm on either side The length of the hub will be 100mm The total length of the whole the assembly with the spoke mounting is 120mm

Material used : The material for the hub will be aluminium as it is light and is more rigid. The material of the spokes is stainless steel as it has to bear the total load and

effectively transfer it to the tyres through the rims.

14.2. Brakes:In order to select an appropriate braking system for our vehicle, we had to consider various brakes on the market that could easily be fitted onto our wheels. Further, the brakes needed to be as light as possible. They should also be compact as the wheels are covered. The logical choice was to go in for three disc brakes, one on each wheel, as they provide sufficient braking force, while satisfying the above mentioned requirements.

Configuration of brakes: We are using three sets of the aforementioned disc brakes, with one set for each wheel. The brakes are readily adjustable, allowing us to set an optimal brake balance. The discs will be mounted (coupled) on the hub shaft of the wheels and the calipers that will hold the disc and thereby stop the wheel from moving will be mounted onto the chassis.Braking force: We estimate a braking force of approximately 0.7g. Our method of calculating this is as follows (for locking of wheels):

Nr = mg (0.47 – µh/l), Nf = mg (0.53 + µh/l)….. Normal forces at front and rear respectivelyF = µ (Nr + Nf)…… Total Breaking ForceOur tires on dry asphalt have µ = 0.7 approx.h = 6” (height of centre of gravity), l = 78” (wheel base)m = 100 kg, fully loaded.

Hence, Nr = 41.61 kgf at the rear wheel and Nf = 59 kgf at the front wheels, combined.

Therefore, F = 71 kgf.Estimated Stopping distance from a speed of 10m/s (36 kmph) = 7.28 m.Estimated Stopping distance from a speed of 4.44 m/s (10 mph) = 1.438 m.


Project Garuda 2011

15. Auto Electricals:

The Eco-Marathon car has certain electrical components like starter motor, rear light, engine kill switch etc. This circuit diagram shows the flow of current from the battery to various components.

16. SAFETY EQUIPMENT:

In a vehicle, it is very important to ensure driver safety. The following measures have been taken:The chassis of the car has been designed to withstand high impact forces in case of the vehicle tipping over. The roll cage has been designed to prevent the driver’s head from coming in direct contact with the ground in case the vehicle topples while at considerably high speeds.Shatterproof materials have been used throughout the body of the vehicle, thus ensuring no harm to the driver from small flying fragments.A 3 point safety harness system is used to hold the driver tightly in his seat. This ensures that in case of impact, the driver stays within the confines of the roll cage.Three kill switches, one inside and two outside the car; ensure fuel cut-off to the engine so as to prevent it from catching fire. Driver wears a helmet and riding glasses for extended safety. A fire extinguisher is also installed within the reach of the driver.A fire wall made of a thick aluminum plate is placed such that it separates the driver from the engine. This prevents overheating of the driver cabin.All the rules, as specified by Shell for the Eco-Marathon competition, have been taken care of.


Project Garuda 2011


Design Report2

Documents

Transcript of Design Report2