sae supermielage

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Team 6: Calvin Supermileage

Final Design Report

Benjamin Beezhold, ME

Jon Hofman, ME

David Kaemingk, ME and CivE

Will Vanden Bos, ME

Jacob Vriesema, ME

Engineering 340 Senior Design Project

Calvin College

9 May 2012

© 2012, Team 6: Calvin Supermileage and Calvin College


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Executive Summary:

The Calvin College 2011-2012 senior design Team 6: Supermileage includes the following seniorengineers: Ben Beezhold (ME), Jon Hofman (ME), David Kaemingk (ME and CivE), Will Vanden Bos(ME) and Jacob Vriesema (ME). In this report the team proposes and documents design solutions forcreating a single-occupant high fuel-mileage car to compete in the annual SAE Supermileage®competition in Marshall, MI. In such a design, the team resolved to minimize inefficiencies that arosefrom tire rolling resistance, aerodynamic drag, and engine performance. The following report outlines

project feasibility as well as highlights design solutions that encompass aerodynamics, engineoptimization, frame design, steering design and power transmission all while observing SAESupermileage® competition rules.


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Table of Contents

Table of Figures ............................................................................................................................................ 4

Table of Tables ............................................................................................................................................. 6

1 Introduction ........................................................................................................................................... 7

2 Project Management ............................................................................................................................. 8

2.1 Team Organization ........................................................................................................................ 8

2.1.1 Team Member Roles in Subcategories ................................................................................. 8

2.1.2 Documentation Techniques ................................................................................................... 9

2.2 Scheduling ..................................................................................................................................... 9

2.3 Budget Management ..................................................................................................................... 9

2.4

Design Norms ............................................................................................................................. 10

2.5 Method of Approach ................................................................................................................... 10

2.5.1 Minimizing Resistances ...................................................................................................... 10

2.5.2 Maximizing Engine Efficiency .................................................................................................. 13

2.5.3 Optimizing Vehicle Operation ............................................................................................ 13

3 Task Specification and Schedule ........................................................................................................ 14

3.1 Project Breakdown ...................................................................................................................... 14

3.1.1 Engine Integration ............................................................................................................... 14

3.1.2 Aerodynamics ..................................................................................................................... 14

3.1.3 Frame Design ...................................................................................................................... 14

3.1.4 Power Transmission ............................................................................................................ 14

3.2 Gantt Chart, Tasks, and Calendar ............................................................................................... 14

4 Design Process .................................................................................................................................... 17

4.1 Aerodynamics and Vehicle Envelope ......................................................................................... 17

4.1.1 Initial Testing ...................................................................................................................... 17

4.1.2 Material Alternatives ........................................................................................................... 19 4.1.3 Final Selection .................................................................................................................... 19

4.2 Frame .......................................................................................................................................... 22

4.2.1 SAE Requirements .............................................................................................................. 22

4.2.2 Frame Overview and Material Selection............................................................................. 22

4.2.3 Overview of Design Process ............................................................................................... 24


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4.2.4 Final Design ........................................................................................................................ 25

4.3 Engine ......................................................................................................................................... 26


4.3.2 Testing ................................................................................................................................. 27

4.3.3 Alternatives ......................................................................................................................... 28

4.3.4 Final Modifications ............................................................................................................. 36

4.4 Steering ....................................................................................................................................... 36


4.4.2 Alternatives ......................................................................................................................... 38

4.4.3 System Selection ................................................................................................................. 40

4.5 Rolling Resistance ...................................................................................................................... 40

4.5.1 Testing and Calculations ..................................................................................................... 41 4.5.2 Alternatives ......................................................................................................................... 42

4.5.3 Final Selection .................................................................................................................... 42

4.6 Electrical Subsystem ................................................................................................................... 44

4.6.1 Engine and Fuel Injector Circuit ......................................................................................... 44

4.6.2 Brake Lights and Starter Circuit ......................................................................................... 45

5 Vehicle Costs ...................................................................................................................................... 46

5.1 Cost Estimation Development .................................................................................................... 46

5.1.1 Registration Costs ............................................................................................................... 46

5.1.2 Body and Frame Costs ........................................................................................................ 46

5.1.3 Wheels/Brakes/Transmission .............................................................................................. 46

5.1.4 Electrical Costs ................................................................................................................... 47

5.1.5 Engine and Powertrain Costs .............................................................................................. 47

5.1.6 Shell Costs .......................................................................................................................... 48

5.1.7 Testing Equipment .............................................................................................................. 49

5.1.8 Total Costs .......................................................................................................................... 49

6 Conclusion .......................................................................................................................................... 50

7 Acknowledgements ............................................................................................................................. 51

8 References ........................................................................................................................................... 52

9 Appendices .......................................................................................................................................... 55


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9.1 Appendix A: Wind Tunnel Stress Calculations .................. ................. .................. ................. .... 55

9.2 Appendix B: EES Order of Magnitude Calculations .................................................................. 56

9.3 Appendix C: MathCAD Frame Calculations ................ ................. .................. ................. .......... 58

9.4 Appendix D: FEA Frame Simulations ........................................................................................ 68

9.5 Appendix E: Detailed Frame Design .......................................................................................... 79


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Table of Figures

Figure 1: Team organization chart ................................................................................................................ 8

Figure 2: Forces acting on the vehicle during operation .................. ................. .................. ................. ....... 11

Figure 3: Power losses ................................................................................................................................ 12

Figure 4: Work breakdown schedule with Gantt chart ............................................................................... 15

Figure 5: Funnelback design isometric view and dimensions (in inches).................. ................. ................ 17

Figure 6: Kammback design isometric view and dimensions (in inches) .................. ................. ................ 18

Figure 7: Drag forces from varied wind velocities in wind tunnel ................ .................. .................. ......... 19

Figure 8: CAD model of final shell design ................................................................................................. 20

Figure 9: Styrofoam mold created and donated by Betz Industries ............... .................. .................. ......... 20

Figure 10: Lamination schedule for upper and lower shell......................................................................... 21

Figure 11: Completed shell utilizing sandwich concept .................. ................. .................. ................. ....... 21

Figure 12: Roll Hoop Requirements ........................................................................................................... 22

Figure 13: Preliminary frame design .......................................................................................................... 23

Figure 14: Beam 1 loading diagram, all dimensions are in inches ......................... .................. .................. 23

Figure 15: Frame Design ............................................................................................................................ 24

Figure 16: Main beam FEA simulation for a 1-inch deep pothole; safety factor of 2.0 .................... ......... 25

Figure 17: Dimensioned Vehicle Chassis (all dimensions in inches) ............... .................. .................. ...... 26

Figure 18: Specified Fuel Bottle and 3.5hp Base Engine ........................................................................... 27

Figure 19: Schematic of a basic engine dynamometer................................................................................ 28

Figure 20: Modification options for the petrol engine .................. ................. .................. ................. .......... 29

Figure 21: Increasing compression ratio provides increased engine efficiency .................. ................. ....... 30

Figure 22: Temperature increases inside the cylinder will likely not cause engine knock ................ ......... 31

Figure 23: A basic carburetor draws liquid fuel into the combustion stream. .......................... ................. . 32

Figure 24: The engine control unit gathers information to determine the timing and amount of fuel ........ 32

Figure 25: Left, a typical fuel injector sprays atomized fuel ............................ .................. .................. ...... 33 Figure 26: Fuel injection is costly and complicated, but more efficient than carburation. ................ ......... 34

Figure 27: Base engine side-valve combustion chamber, offset from cylinder ........................... ............... 35

Figure 28: Combustion chamber designs: (a) wedge chamber, (b) hemispherical head, (c) bowl in piston,and (d) bath-tub head (Stone, 104). .................. ................. .................. ................. .................. ................. .... 35

Figure 29: Test track for Supermileage® competition ............................................................................... 37


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Figure 30: Maneuverability course ............................................................................................................. 38

Figure 31: Wagon style steering mechanism .............................................................................................. 39

Figure 32: Knuckle steering system ............................................................................................................ 39

Figure 33: A knuckle steering system implemented in vehicle ............... .................. .................. ............... 40

Figure 34: Contact area and rolling resistance ............... .................. ................. .................. .................. ...... 41

Figure 35: Rolling resistance test fixture .................................................................................................... 41

Figure 36: Optimum tire diameters ............................................................................................................. 43

Figure 37: Engine and fuel injector circuit diagram ................................................................................... 44

Figure 38: Engine and fuel injector vehicle circuit layout .................. ................. .................. ................. .... 44

Figure 39: Brake lights and engine starter circuit diagram ................. ................. .................. ................. .... 45

Figure 40: Brake lights and engine starter vehicle layout ................ ................. .................. ................. ....... 45


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Table of Tables

Table 1: Key design variables ..................................................................................................................... 13

Table 2: List of project tasks with estimated time allocations ................. .................. .................. ............... 16

Table 3: Rolling resistances ........................................................................................................................ 42

Table 4: Registration costs .......................................................................................................................... 46

Table 5: Body and frame costs ................ ................. .................. ................. .................. ................. ............. 46

Table 6: Wheels/Brakes/Transmission/Steering Costs ............................................................................... 47

Table 7: Electrical Costs ............................................................................................................................. 47

Table 8: Engine and Powertrain Costs ........................................................................................................ 48

Table 9: Shell Costs .................................................................................................................................... 48

Table 10: Testing Equipment Costs ............................................................................................................ 49


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1 Introduction

On July 29, 2011, President Obama announced that automakers have agreed to increase car fuelefficiency to 54.5 mpg by 2025 ( NHTSA ). A drastic increase over today’s efficiency standards, thismove underscores an increasing need to reduce the demand for fossil fuels. Pessimistic analysis ofworldwide supply estimates that peak oil production has already occurred ( Aleklet ). With alternativeenergy vehicles slowly making their way to showroom floors, engineers need little convincing of thesignificance of highly efficient cars. It is in this light that the Society of Automotive Engineers (SAE)sponsors the SAE Supermileage® competition. Engineering students from across North America designa high efficiency, single-occupant vehicle: the best combination of fuel economy, written and oral

presentation wins. The team represented here designed and built a vehicle to participate in thiscompetition for their Senior Design Project. A few broad outcomes of such a project includedovercoming design difficulties, expansion of knowledge in respective design niches, and interpersonalgroup management.

This senior design project fulfills the capstone requirement for senior engineering students at CalvinCollege. The class is divided into two sections: ENGR 339 during the Fall semester and ENGR 340during the Spring semester. Class time in ENGR 339 was spent teaching senior engineering students howto work as a team. Lectures and discussions address topics such as communication, safety and projectmanagement. ENGR 340 focused more on vocation and also allocated the majority of class-time to

building a prototype. The following sections document the feasibility, design, and implementation of this project.


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2 Project Management

2.1 Team Organization

The Calvin College Supermileage senior design team consists of five mechanical engineers. Design and

analysis work was divided into five subcategories based on team members’ skills, interests, and previousinternship experience. Figure 1, below, shows the organization chart of Calvin Supermileage along withsupporting faculty and mentors.

Figure 1: Team organization chart

2.1.1 Team Member Roles in Subcategories

Ben Beezhold : hails from Seattle, Washington and worked extensively on the shell and aerodynamicsdesign throughout this project. His degree in engineering with a mechanical concentration andinternational designation will be put to the test as he begins working full-time as a structural designengineer at Boeing, also in Seattle.

Jon Hofman : Jon is a fifth year senior graduating with a degree in engineering - mechanicalconcentration and a music minor. In this project, he oversaw all things engine: testing, modification,


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installation, and operation. He lives in Zeeland, MI with his wife Julie and son William. He anticipatesworking full time at Gentex upon graduation.

David Kaemingk : David is a fifth year senior and will be graduating with concentrations in civil andmechanical engineering and mathematics minor. David primarily worked on the design and fabrication ofthe vehicles frame. He eagerly anticipates marrying Tara Meyering this summer as well as working atGentex upon graduation.

Will Vanden Bos : has greatly enjoyed working on a team developing a more fuel-efficient vehicle. Willworked mainly with designing steering and powertrain components, and also helped extensively with thevehicle shell construction. He is passionate about sustainable energy practices, especially with regard tothe automotive industry, and is excited to begin working at Gentex Corporation after graduating in May.

Jacob Vriesema : worked extensively on the CAD models, tire selection and electrical components aswell as helped with much of the paperwork and shell. He hopes to work with energy efficiency somedayor become a CAD consultant.

2.1.2 Documentation Techniques

Accountability for reaching project goals often took the form of informal meetings three days a week.Team meetings were held each weekend. In the early stages of the project, these meetings mostlyconsisted of brainstorming sessions and research. Additional meetings were often called in order to

prepare various assignments for the ENGR 339 class. As time went on into ENGR 340, meetings becamealmost daily. At these meetings, important notes were written down and emailed out to the team, as wellas saved in the t eam folder on one of Calvin’ s Servers (Shared/Engineering/Teams/Team06). Note thatall project documents were saved in this folder.

2.2 Scheduling The ENGR 339 and ENGR 340 course schedule and assignments served as the framework for schedulingtasks throughout the duration of this project. Course assignments helped move the project from conceptto completion. With such assignments serving as the framework, each task was assigned an estimatedlength of time for completion. These assignments provided a schedule with concrete deadlines and alsoserved as project milestones. In ENGR 339, a program called OpenProj was used to create a Gantt chartto schedule tasks. The goal here was to break milestones into tasks with a maximum execution time of 8hours, in order to help emphasize the critical essence of time. Unfortunately, this method did not provevery beneficial to the team. The chart became very unwieldy with so many items, and as special softwarewas needed open it, it was not viewed very often. This resulted in missed deadlines and late tasks.However, in ENGR 340, the team switched to Google Calendar to schedule tasks. This proved to be a

much more beneficial tool. Having the schedule overlaid on a calendar really helped visualize when taskswere due, and the ease of access allowed it to be checked much more frequently. This method was usedwith great success for the remainder of the semester.

2.3 Budget Management

The crux of every project is its budget. Originally, Will Vanden Bos set up an estimated budget that wasupdated and adjusted throughout the semester. At the beginning of ENGR 340, a preliminary budget wasapproved. The team then kept track of all purchases in a spreadsheet stored on the Team Folder


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(Shared/Engineering/Teams/Team06/Budget) in order to keep spending documented and accountable.Section 5.1 (Cost Estimation) provides an in-depth look at estimated costs and budgeting.

2.4 Design Norms

As Christian Engineers, the team has a calling to create designs that have significance and fulfill thecultural mandate. Their design pushed to incorporate the following principals in the design of their high-mileage vehicle.

Stewardship : The overall intention of the vehicle should demonstrate careful use of the Earth’sresources. The entire project was framed by this idea of stewardship as they strove to alleviatedependence on fossil fuels.

Integrity : As a team, they strove to promote honesty and professionalism interacting with eachother, the professors, and any outside companies and consultants. They tried to display goodcharacter and sportsmanship throughout the course of the project, and hope to continue this at theSupermileage® competition.

Transparency : By maintaining an open stream of communication with all who were involved inthis project, they strove to produce consistent, reliable, and predictable solutions.

2.5 Method of Approach Maximizing the fuel efficiency of the vehicle can be addressed in the following ways:

1. Minimizing the resistances acting on the vehicle2. Maximizing the engine’s efficiency3. Optimizing vehicle operation in accordance to competition requirements

Because of time and budget constraints, team Supermileage performed a preliminary analysis to identifythe factors that have the greatest potential to affect fuel economy. This analysis set a basis for projectdirection and more in-depth analysis and testing.

2.5.1 Minimizing Resistances

The significant inefficiencies opposing the vehicle motion are wind resistance, rolling resistance from thewheels, bearing resistance, and power transmission losses. These are depicted as equivalent forces inFigure 2.


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Figure 2: Forces acting on the vehicle during operation

A major aspect of the 2011-12 Supermileage vehicle was formulation of a design that minimizes theseresistances. An order of magnitude analysis was performed for the resisting forces using Equations 1-3.

2

2V AC F pro jd drag

Eqn. 1

V C F rr rr

Eqn. 2

N bbearing F C F Eqn. 3

Note that C d , C rr , and C b are coefficients of drag, rolling resistance, and bearing resistance, respectively.Variables A proj , F N , and V represent the projected frontal area of the vehicle, normal force, and vehiclevelocity. All these combine to form design variables for this project. Studies were done to determine thetradeoffs between these design variables. The values which minimize resistances were then used in thedesign of the vehicle. Results showed that at lower velocities, resistance due to rolling resistancedominated. However, at a certain velocity (approximately 24mph) losses from aerodynamic dragdominated. Figure 3 shows each resistance as a function of velocity.


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Figure 3: Power losses

Assumptions made in this analysis are displayed in Table 1. Power loses were also calculated toilluminate efficiency “offenders.” Note that the estimated range column specifies a maximum andminimum value for each variable. The estimated power loss range column lists the power lossesassociated with the maximum and minimum values. The difference in power loss column represents thedifference between the maximum and minimum values and therefore represents the sensitivity of thatvariable to power loss.


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Table 1: Key design variables

Design Variables SymbolAssumed

ValueEstimated

RangeEstimated PowerLoss Range [W]

Difference inPower Loss [W]

Vehicle Mass [kg] M vehicle 52.2 40 - 90 63 77 14

Vehicle Velocity [m/s] V 6.7 6.7 - 11.2 69 163 94

Coefficient of Drag C d 0.12 0.1 - 0.25 66 86 20

Projected Area [m 2] Aproj 0.75 0.5 - 1 63 74 11

Rolling ResistanceCoefficient

Crr 0.0055 0.005 -0 .01 65 102 37

Coefficient of BearingFriction

Cb 0.00050.0001 -

0.00160 63 3

This analysis suggested that aerodynamic drag and rolling resistance have the greatest effect on the carwhile bearing resistance is less significant. Therefore our team focused on reducing aerodynamic drag androlling resistance.

The easiest and most effective way to reduce aerodynamic drag is to simply reduce the vehicle ’s projectedarea. Other factors which effect aerodynamic drag are more difficult to quantify using basic calculations,such as the effects of surface texture and humidity.

At low velocities, rolling resistance is the largest resistance on the vehicle. Therefore, much time wasdevoted to selecting wheel components (e.g. wheel diameter, width, and tire pressure) and minimizingvehicle weight.

The preliminary resistance calculations described above did not consider the effects of wheel alignment ortransmission losses. However, these factors still required design work and will be discussed in greaterdetail in their respective sections.

2.5.2 Maximizing Engine Efficiency

Preliminary calculations suggested that increasing the efficiency of the engine by 1 percent would resultin an increase of fuel economy by roughly 86 mpg (see Appendix B for calculations). For this reason,Team Supermileage spent significant time maximizing the fuel efficiency of the engine. With the help ofBaker Engineering, the team was able to attach the engine to a dynamometer coupled with fuel and air

flow rate instrumentation in order to determine the vehicles optimum operating rpm.

2.5.3 Optimizing Vehicle Operation

The competition requirements state that the vehicle must maintain an average velocity between 15mphand 25mph. Rolling resistance and aerodynamic drag are proportional with velocity and thus areminimized when velocity is minimized. However, maintaining 15mph may require the engine to operateat a less than ideal rpm. Many successful teams in the past have approached this problem by fine tuning


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gearing in the transmission as well as coasting and accelerating alternately. This allows the engine tooperate around its most efficient rpm. The team plans on implementing this coast and burn strategy whenthey compete in the SAE Supermileage® competition.

3 Task Specification and Schedule

3.1 Project Breakdown

In working towards the ultimate goal of high fuel efficiency, the team divided major vehicle componentsinto subsystems. This helped clarify design and research needs. Subsystems included the following:Engine Integration, Aerodynamic Design, Frame Design, and Power Transmission.

3.1.1 Engine Integration

The Engine Integration team handled engine modifications and engine testing procedures. Mostimportantly, this group worked with Baker Engineering to test the engine on a dynamometer. This device

recorded the amount of fuel used for different engine power outputs, driving efficiency and performanceoptimizations.

3.1.2 Aerodynamics

The Aerodynamics group focused primarily on devising test methods to confirm design decisions relatingto decreasing aerodynamic drag. Wind tunnel tests were one method by which this was attempted. Inaddition, this group decided which material to use for the vehicle shell and how to fabricate the entirevehicle envelope.

3.1.3 Frame Design

Team members working on the frame design subsystem were concerned primarily with creating alightweight yet durable frame that meets competition rules. The main tradeoff for this subsystemincluded balancing material properties with weight. Steering design and wheel selection also took placein this group.

3.1.4 Power Transmission

While the engine integration group looked at modifications to the engine, the power transmission groupfocused on how to efficiently transmit power from the engine to the wheels. Shifting speeds andcoast/burn techniques were also considered in this group.

3.2 Gantt Chart, Tasks, and Calendar

As discussed earlier, a Google Calendar was used to schedule tasks and meetings for ENGR 340 in placeof the Gantt chart system. Please see the Team Folder (Shared/Engineering/Teams/Team06) forscreenshots of this calendar. An example of how the team separated deliverables with time can be foundin Table 2, below, while Figure 4 shows the work breakdown schedule (as of December 9, 2011).


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Figure 4: Work breakdown schedule with Gantt chart


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Table 2: List of project tasks with estimated time allocations

TASK NAMEHOURS PER

PERSON

Engine Research:

Research designs from previousteams

6 hours

Research fuel injection 6 hoursResearch Increasing compressionratio

6 hours

Research carburetor devices 6 hours

Begin contructing a dynomometer 10 hours

Engine Implementation:

Test engine with dyno 7 hours

Generate and interpret dyno data 5 hours

Modify engine componants 10 hours

Adjust to get best MPG 10 hours

Test adjustments 10 hoursIterative adjustment and tests 10 hours

Aerodynamic Research:Research aerodynamic conceptsand equations

10 hours

Determine how coefficient of dragand lift affect vehicle

8 hours

Design 2 shapes: models with

interior / exterior wheels

6 hours

Draw 2 shapes in CAD 2 hoursCreate 3D plots using SteelcasePrinter

-

Create list of wind tunnelcomponents

1 hour

Aerodynamic Implementation:Build a wind tunnel test section 10 hoursPerform wind tunnel tests 8 hoursGenerate and interpret windtunnel data

2 hours

Make recommendation on bodyshape

-

Engine Work:

Aerodynamics Work:

TASK NAMEHOURS PER

PERSON

Materials Research:

First order calcs for chassis design 2 hours

Determine 3 material choices 8 hours

Research steering assemblies 7 hours

Research braking assemblies 7 hoursDetermine frame design andmaterial

8 hours

Materials Implementation:Order of magnitude calcs forvarious materials

6 hours

Choose prefered chassis design 6 hoursConstuct a CAD model of thevehicle 8 hoursPerform FEA analysis on keycomponents

8 hours

Obtain materials 4 hoursConstruct chassis 10 hoursConstruct shell 10 hoursCons truct steering as sembly 5 hours

Construct braking assembly 5 hours

Optimization Implementation:

Test Vehicle 20 hoursModify/Optimize vehicle based ontesting

20 hours

Race in Competition 8 hours

Verbal presentation #1 1 hourVerbal presentation #2 1 hour

Prepare PPFS 20 hours

PPFS Draft Due -

Verbal presentation #3 1 hourVerb al presentation #4 1 hourPrepare final paper 20 hours

Materials Work:

Optimization Work:

Documentation:


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4 Design Process

4.1 Aerodynamics and Vehicle Envelope

The success of teams entering the Supermileage competition depends heavily upon minimization of fuel

consumption. Two key design elements in this include the shape of the vehicle shell (coined “vehicleenvelope”) and its total weight. If projected area is large, the vehicle’s drag will also increase. Inaddition, increasing shell weight has a negative impact on rolling resistance (See section 4.5). Thefollowing subsections describe initial testing, material selection, and final design specifications.

4.1.1 Initial Testing

Most Supermileage vehicles fall into two categories: wheels internal to the shell and wheels external tothe shell. The Aerodynamics group decided that an ideal way to test these alternatives was with Calvin’swind tunnel under the supervision of Professor DeJong. Two models were created using Pro/Engineersoftware. Steelcase Inc. assisted in manufacturing these models using a Fused Deposition Modeling

(FDM) machine. The first vehicle modeled internal wheels and was called the Funnelback design. Sincethe shell must cover the internal wheels, its projected area was relatively large. Figure 5 illustrates thefirst model.

Figure 5: Funnelback design isometric view and dimensions (in inches)

The second model placed the wheels outside the envelope of the shell. It utilized what is known as aKammback design. Kammback technology, embodied on hybrid vehicles such as the Toyota Prius and


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the Honda Insight, has been shown to increase fuel efficiency by forcing the air to separate from the endof the chassis sooner. Figure 6 illustrates the second model.

Figure 6: Kammback design isometric view and dimensions (in inches)

The above models were tested using Calvin College’s wind tunnel over a range of velocities from roughly40mph up to 110mph. The resulting force of drag was detected using strain gages mounted inside a teststructure. Equation 4 could then calculate a drag coefficient:

pro j

d d Av

F C 2

2

Eqn. 4

Where F d is the drag force, is the density of the air, and A proj is the projected frontal area. While the

notion of finding a clear winner between the two test models might seem straightforward, the test results

were not indicative of such information (See Figure 7, below).


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Figure 7: Drag forces from varied wind velocities in wind tunnel

Vibrations affecting the test equipment and imprecisions in the measurement techniques causeduncertainty to propagate throughout the results. Since forces cannot be negative, sensible data shouldonly be observed above the x-axis. Note that these inconsistences could be the result of inaccurate windtunnel calibrations. Given more time, this team would have pursued retests.

4.1.2 Material Alternatives

Before proceeding onto shell shape design, it was important to first select a building material. While

some materials could be used in most any design, others might present challenges in the presence ofcontoured surfaces. The primary materials of choice were the following: acrylic, fiberglass, Dacron, andcarbon fiber. In all these choices, the best candidate ought to demonstrate high rigidity, light weight, andlow cost. While acrylic would be ideal for a canopy-type cockpit for the driver, its manufacturability isextremely low and its density is quite high. Fiberglass presents an excellent lightweight choice forgeneral use. However, initial testing using small curved molds indicated that fiberglass could notmaintain its integrity around a tightly curved surface. While carbon fiber would present an extremelystrong and lightweight solution, funds were unavailable for such an exorbitant cost. Finally, Dacron wasselected because it fulfilled all three specifications; Dacron also exhibits heat-shrinkability. The finaldesign utilized Dacron laminated with epoxy.

4.1.3 Final Selection

Using CAD software, the final aerodynamic shape was formed around the completed frame. Thisallowed our group to visualize exactly where components such as wheels, roll bars, and engines needed to

be placed. The final shape integrated several inspirations: aspects of the wind tunnel models, smallairplane nose design, and vehicle designs from top Supermileage competitors. In the end, this group

-1

-0.5

0

0.5

1

1.5

2

2.5

40 50 60 70 80 90 100 110

D r a g

F o r c e

[ N ]

Wind Velocity [mph]

Drag Forces of Two Models

Kammback

Funnelback


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produced a CAD model with an aerodynamic shell that perfectly fit outside the frame. Note that the finaldesign placed wheels inside the shell. Figure 8 shows such CAD model.

Figure 8: CAD model of final shell design

Note also that the internal wheels are shielded frontally by fairings. This will ideally ensure that theairflow around the wheels remains undisturbed.

Typically when working with a laminated material like Dacron, the builder uses a mold to shape the cloth.The process of laminating includes pinning Dacron to a mold, heat shrinking until taut, then applying athick coat of epoxy; together these form a single layer. Betz Industries (a Grand Rapids, MI foundry)

played a significant role in mold fabrication. Using enormous Computer Numerical Control (CNC)machines, Betz created a 1:1 Styrofoam model per our CAD design. Figure 9 shows Betz’s contribution.

Figure 9: Styrofoam mold created and donated by Betz Industries

The final shell design also utilized a theory called sandwich concept. In an effort to maximize thematerial’s efficiency, the two faces were “placed at a distance from each other to increase the moment of


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inertia, and thereby the flexural rigidity, about the neutral axis of the structure. A comparison could bemade with a solid beam.” 1 Thus the lamination schedule was as follows: 1 layer Dacron, 1 layer of 1/8 th inch thick polyvinyl foam, 1 layer Dacron, finished with extra coats of epoxy. A schematic of thislamination schedule is shown in Figure 10.

Figure 10: Lamination schedule for upper and lower shell

When creating the shell, the team resolved to implement a monocoque structure. In other words, thestructure would remain rigid without the help of internal structural members but rather would derive itssupport through a continuous, rigid form. This design primarily works to reduce shell weight. Ultimately,white paint was added for aesthetics. Figure 11 illustrates the finished shell (pre-paint).

Figure 11: Completed shell utilizing sandwich concept

1 "DIAB Sandwich Handbook." DIAB, 3 Sept. 1952. Web. 8 May 2012..


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4.2 Frame

The frame is an integral part of the vehicles design; it must provide the adequate structural integrity tosupport vehicles loads, provide the overall shape of the vehicle, and satisfy competition safetyrequirements. In addition, rolling and bearing resistances are proportional to the vehicles weight and thusit is advantageous to reduce the vehicles total weight. For these reasons, material selection and a carefuldesign is important to the overall success of the vehicle.

4.2.1 SAE Requirements

Competition requirements mandate a roll bar that extends a minimum of 5 cm above the driver’s helmetand is wider than th e driver’s shoulders as shown in Figure 12. The entire vehicle must also withstand a250 lbf force applied to the top of the roll bar at any angle. The vehicles structure must also include asteel or aluminum fire wall that completely separates the driver from the engine. (SAE, 16-17).

Figure 12: Roll Hoop Requirements

4.2.2 Frame Overview and Material Selection

Early in the design phase the team selected a teardrop-shaped vehicle design utilizing a three-wheeledconfiguration as show in Figure 13. The vehicle is divided into front and rear sections by the roll

bar. The driver, two front wheels, and a four bar linkage steering assembly occupy the front half of thevehicle. The rear section houses the engine, starter motor, batteries, fuel container, power transmission,and the driven rear wheel.


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Figure 13: Preliminary frame design

The frame team developed a basic failure analysis of the main beams of the vehicle. The goal of thisanalysis was to guide the team’s selection of feasible materials for the rest of the frame. Figure 14 showsa simplified diagram of the main beams approximated loads. In this analysis, the beam was assumed to

be simply supported at both ends and all of the loads were assumed to be static with the exception of thedriver which was analyzed as an impact force calculated using the energy method as shown in Equation 5.

[ √ ] Eqn. 5Where δst is the static deflection resulting from the weight of our driver, h is the height the load is fallingfrom, and n is a correction factor. A height of 1 inch was assumed in the analysis — this accounts for thedriver entering and exiting the vehicle as well as simulating the vehicle encountering uneven roads and

pot holes (Norton108-111).

Figure 14: Beam 1 loading diagram, all dimensions are in inches


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4.2.3 Overview of Design Process

After selecting GR Iron and Steel as our aluminum supplier, the frame team iterated through severalcomprehensive designs. This iterative process included hand calculations, Autodesk Simulation finiteelement analysis, and reviews with Phil Jaspers and Richard DeJong. Considering the lifetime of this

vehicle is under a year, fatigue was not considered in this analysis. The frame design was split into threemain assemblies: main beams, front end, and roll bar as seen in Figure 15.

Figure 15: Frame Design

The main beam assembly is composed primarily of two 1.5in x 1in x 1/8in channels connected by rigidity braces. These beams support the weight of the driver, engine, and powertrain and are most susceptible tofailure in bending when loaded dynamically by the driver or by road conditions. The beams are designedto withstand an impact load resulting from the vehicle hitting a 1 inch pothole with a safety factor of 2 asseen in Figure 16. This analysis is conservative as it does not include the additional supports added to thechannels, nor the effect of the sway bars. See Appendix D and E for complete frame drawings and

detailed stress analysis of each assembly.


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Figure 16: Main beam FEA simulation for a 1-inch deep pothole; safety factor of 2.0

4.2.4 Final Design

The final dimensioned chassis design can be seen in Figure 17 showing a side, front, and top view. Theside view includes the approximate profile of how the driver fits into the vehicle.


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Figure 17: Dimensioned Vehicle Chassis (all dimensions in inches)

4.3 Engine


Each SAE Supermileage team is given a common engine, donated by the Briggs and StrattonCorporation. The 3.5hp base engine (Figure 18, below) is four-cycle, air cooled, carbureted, and equippedwith side-mounted valves. Teams may modify the base engine within certain bounds. For example, the

piston and crankcase may be machined or altered, but must still be identifiable as components of the baseengine. In addition, a common fuel bottle is provided to each team at the competition. Design of theengine and body must allow for the swift (45 seconds) removal and replacement of the fuel bottle so thatcompetition organizers can easily measure fuel usage at the competition.


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Figure 18: Specified Fuel Bottle and 3.5hp Base Engine

4.3.2 Testing

Internal combustion engines have been the subjects of over a century of research and implementation, both by academia and the automotive industry. Engine efficiency is often a function of manyinterdependent features and components; theoretical analysis can be very complicated and unreliable. Forthis reason, the team decided to implement the use of an engine dynamometer. With the ability toempirically test the engine, the team would be able to objectively quantify engine improvements.Additionally, the team could discover optimum engine operation parameters, e.g. the rpm at which the

engine performs most efficiently.

Dynamometers are extremely expensive and hard to make. Fortunately however, a local business, BakerEngineering Inc, from Nunica, MI, was receptive to the idea of partnering with the team in testing andmodifying the engine. They have professional-quality small engine dynamometer test equipment. BakerEngineering has years of experience designing and building performance gas engines, both large andsmall.


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Figure 19: Schematic of a basic engine dynamometer

Similar to that of Figure 19, a dynamometer couples the petrol engine to a DC motor. The power then can be dissipated through resistance wires powered by the DC motor. Because the motor is mounted on non-fixed trunnions, a fixed lever-arm mounted to the DC motor gives the torque acting on the motor byapplying a force to the load cell. A tachometer then measures the angular velocity of the output shaft.The engine power then, is given by Equation 6, when ω is in radians per second.

Eqn. 6

From this equation, the peak engine power can be found as a function of rpm. To find peak efficiency, therate at which fuel is consumed must also be measured. The addition of a fluid flow-meter giving the fuelconsumption rate can give the effective fuel-volume efficiency (Joules/mL), calculated by Equation 7.

̇ Eqn. 7

By using a dynamometer, Calvin Supermileage had the ability to quantify any modifications made to theengine. This allowed the team to definitively know if a modification had improved the efficiency of theengine. By running the engine at different rpms, the team was able to determine the most efficient enginespeed. This information was then used when designing the gear ratios in the transmission and power train.

4.3.3 Alternatives

Of the hundreds of ways the engine could be modified, the team chose just three to consider. Many otheroptions exist, but time and budget constraints forced the team to limit the scope of possible enginemodifications to those that initially seemed most feasible, effective and affordable. Figure 20 shows the

options considered.


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Figure 20: Modification options for the petrol engine

Compression Ratio and “Running Lean”

Without any major design modifications to the engine itself, certain parameters can be adjusted toincrease fuel efficiency. With fuel delivery executed by the carburetor, adjustments can be made to the

air-to-fuel mass ratio or AFR.

̇ ̇ Eqn. 8When the AFR matches the molecular ratio for a complete combustion of the fuel, it is called thestoichiometric AFR, and is about 14.7:1 for gasoline (Stevens). Typically, a richer AFR (more fuel and asmaller AFR) can produce more power, while a leaner AFR can product more efficiency. The AFR for

best efficiency varies from engine to engine and is a function of many design variables. Modern cars havefound peak efficiency anywhere from 15.7:1 to 17.6:1 (Stevens, and Edgar). The team, using thedynamometer, could adjust the carburetor to test various AFRs and establish the best ratio for fuel

efficiency.Another engine modification under consideration was the compression ratio. The compression ratio is theratio of the cylinder volume at the bottom of the stroke (bottom dead center, or TDC) to the volume at thetop of the stroke (TDC), Equation 9 (Cengel, 361).

Eqn. 9

A higher compression ratio results in greater pressures during the combustion phase of the engine cycle.The CR could be increased by adding material (through welding) to the combustion chamber, thusreducing the V TDC . These higher pressures can in turn result in greater energy release from the combustion

cycle. In an ideal engine cycle (Otto cycle) with air modeled as an ideal gas, the efficiency of the engineis given by Equation 10 (Cengel, 361). Here, k is a constant specific heat ratio for gasoline equal to 1.4.

Eqn. 10

Even though no engine can perform as thermodynamically ideal, it is interesting to see the increase inefficiency as a function of compression ratio. The base engine provided by Briggs and Stratton has acompression ratio of 6:1 (Briggs and Stratton FAQ); increases up from 6 are shown in Figure 21.


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Figure 21: Increasing compression ratio provides increased engine efficiency

There are several drawbacks to increasing the compression ratio. First, an increase in CR drives anincrease in cylinder pressure during the engine cycle. The materials and construction of the engine headand cylinders might not withstand the pressure increases. Second, with the pressure increases cometemperature increases. At higher temperatures, engine components see greater stresses and could melt. Inaddition, if the fuel reaches its auto-ignition temperature before the spark plug fires, a spontaneouscombustion could take place creating engine knock. Figure 22 shows the nominal ignition temperature(Transportation Energy Data, 1) for the competition fuel (isooctane) in relation to the increasedtemperatures.

In a thermodynamically ideal engine model, any compression ratio greater than 8 could producetemperatures above the auto ignition temperature for isooctane. Several things, however, will likely allowfor these high temperatures. First, the actual engine is not thermodynamically ideal and will therefore loseheat loss during the compression cycle. Note also that the temperature will not increase as dramatically asshown in these calculations. Second, the nominal ignition temperature is not measured in conditions at allsimilar to the inside of an engine, and may in fact be several hundred degrees higher than nominal (Smythand Bryner 247). Because of this, it is not likely that engine knock will be a problem.

0%

5%

10%

15%

20%

25%

30%

6 7 8 9 10 11 12 13 14

Compression Ratio

Efficiency Increase with Higher Compression Ratios


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Figure 22: Temperature increases inside the cylinder will likely not cause engine knock

F uel I njection

The stock 3.5hp Briggs and Stratton comes with a fixed jet carburetor. Essentially, carburetors deliverfuel to the combustion chamber as a function of the flow-rate of air into the cylinder. The intake air passesthrough a venturi “throat” in the carburet or. The increase in air velocity creates a pressure drop whichdraws in liquid fuel through a small orifice in the sidewall. The flow-rate of the air (controlled by the

throttle) then determines the amount of fuel drawn into the combustion stream. The carburetor can beadjusted (as suggested above) to different proportions of fuel and air (AFR, air-fuel ratio). A basicdiagram of a carburetor is found in Figure 23.

Corrected AI temperature = 1291 deg F

Nominal AI temperature = 781 deg F


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Figure 23: A basic carburetor draws liquid fuel into the combustion stream.

Fuel injection is another technology for delivering fuel to the combustion stream, but does so quitedifferently from carburation. Whereas the carburetor draws liquid fuel into the air with a venturi pressuredrop, a fuel injector uses tiny jets to atomized the fuel and spray it into the combustion stream based on

parameters such as air flow rate, engine speed, throttle, temperature and others (Stone, 122). The parameters are measured with sensors and processed by an engine control unit, or ECU. The ECUdetermines the amount of fuel to inject based on algorithms programmed into the ECU. The flow diagramshowing a fuel injection system is shown in Figure 24.

Figure 24: The engine control unit gathers information to determine the timing and amount of fuel

The injector can either be located before the intake valve (port injection) or as part of the combustionchamber itself (direction injection). In either case, atomized fuel is mixed with air for combustion in thecylinder, Figure 25.


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Figure 25: Left, a typical fuel injector sprays atomized fuel 2

For maximum efficiency, fuel injection has several advantages over traditional carbureted engines. First,the fuel is atomized when ignition occurs versus a liquid fuel mixture in carburation. This atomized fuel

burns more efficiently than liquid fuel and results in greater engine efficiency (Walton, 98). Second, fuelinjection is much more responsive to the operating environment; the ECU can vary the amount of fuel

based on sensor data and react instantly to changes in temperature and pressure. This means less wastedfuel, and better AFR at all operating speeds. Third, there is no venturi “throat” that constricts the intakeflow which results in easier engine “breathing” and l ess flow-power loss.

Unfortunately, converting a carbureted engine to one with fuel injection is no easy task. A host of newengine components must be affixed to the engine: sensors, injections, pumps, an ECU, etc. It would be achallenge merely to get all these new components to work together to that the engine operates at all; it isanother challenge to optimize the operation so that the engine runs more efficiently. Figure 26 showssome pros and cons of fuel injection fuel delivery system.

2 http://upload.wikimedia.org/wikipedia/commons/2/29/Injector3.gif) . Middle: direct injection sprays fuel into the cylinder. Right, port injectionsprays fuel upstream of the intake valve (Walton, 99)

http://upload.wikimedia.org/wikipedia/commons/2/29/Injector3.gifhttp://upload.wikimedia.org/wikipedia/commons/2/29/Injector3.gifhttp://upload.wikimedia.org/wikipedia/commons/2/29/Injector3.gif


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Figure 26: Fuel injection is costly and complicated, but more efficient than carburation. 3

Without the advice of engineers at Baker Engineering Inc., it is unlikely that Calvin Supermileage would be able to convert the engine to run with fuel injection.

Combustion Chamber and H ead

The Briggs and Stratton base engine has a side-valve arrangement, similar to the one shown in Figure 27. In this arrangement, the valves and spark plug are offset from the center of the piston. The theoreticalfluid dynamics involved in the flow and combustion are very complicated and difficult to performaccurately. Despite this, there are some generalizations than can be made about combustion chamberdesign.

Side valve configurations have an upper limit of 6:1 for the allowable compression ratio. This is becausethe explosion trajectory is not in line with the piston motion, and the zero- clearance “squish” region onone side of the piston can cause pockets of high pressure resulting in engine-knock (Stone, 100). Inaddition, the flow of the air-fuel mixture can create poor burn profiles in a side-valve configuration. Manyother designs exist, each with a particular design benefits. Figure 28 shows several common combustionchamber designs.

For maximum efficiency, it is important to ensure an even fuel mixture throughout the chamber, minimizeflow-power losses through valve and port design, and low-mechanical wear (Stone, 100. Pulkrebek, 249,Second Chance Garage. Morgan.). With the cooperation of a local machine shop, Calvin Supermileagewould be able to design a new combustion chamber with an overhead valve configuration. Additional

3 Stone, 121. Walton, 95-99, Pulkrebek, 179-181


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design would be needed to arrange the valve push-rods. Both designs (a) and (b) could be implementedwith the need for additional piston modification. Head modifications are quite common among

performance enthusiasts, and so the feasibility is quite high for this engine modification.

Figure 27: Base engine side-valve combustion chamber, offset from cylinder

Figure 28: Combustion chamber designs: (a) wedge chamber, (b) hemispherical head, (c) bowl in piston,and (d) bath-tub head (Stone, 104).


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4.3.4 Final Modifications

Calvin Supermileage examined several options for engine modification, and determined the need fordynamometer testing. They also implemented a new carburetor and exhaust, new flywheel and starter,and an altered head design.

A Mikuni carburetor was installed in place of the standard. It offers an adjustable air-to-fuel ratio (AFR).Maximum efficiency is typically produced by “running lean,” i.e. running the engine with excess air.During dynamometer testing, an oxygen sensor was used to monitor the AFR. Depending on theatmospheric conditions, maximum engine efficiency was found with and AFR between 16:1 and 17:1.This ensures that the fuel is as completely burned as possible. The carburetor was mounted to the intake

port with a straight-shaft aluminum intake, fabricated by the team.

To start the engine during the competition run, an electrical starter was needed. The stock engineflywheel was replaced with a purchased flywheel that had starting teeth on one side. The electric starterwas mounted to a custom bracket fit to the engine. The starter is powered by a 12V battery, and can befired by a switch mounted on the steering column of the vehicle.

To increase the engine efficiency, the head was modified for higher compression ratios. The stock B&Sengine has a compression ratio of 6.6:1. The engine head was filled in with aluminum weld, bringing thecompression ratio up to 7.2:1.

4.4 Steering


The steering mechanism is an important characteristic of the vehicle, which must both enable safe andeffective maneuvering of the car, and satisfy the specifications set out by SAE. The track that the vehicle

will compete on is a 1.6-mile oval test track shown in Figure 29, below.


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Figure 29: Test track for Supermileage® competition

This in itself doesn’t require much of a turning radius, however the vehicle must also pass amaneuverability course before it is allowed to compete. This course, as illustrated in Figure 30, consistsof completing an untimed 180 degree turn, and then weaving in and out of 4 cones placed 25 feet apart inunder 15 seconds.


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Figure 30: Maneuverability course

In order to successfully complete this course then, the vehicle must have a maximum turning radius of 50ft. Another requirement by SAE is that the steering must have a “natural” response. In other words, if thedriver turns the steering wheel left, the car will go left, and vice-versa.

4.4.2 Alternatives

As the basic components of the Supermileage vehicle are quite similar to a go-kart, go-kart steeringsystems were studied and analyzed. There are two main designs for go-kart steering systems: WagonStyle systems, and steering knuckle systems.

Wagon Style System:

The first type of system is the most classic, but also the most elementary. This simple system simplyconsists of two wheels permanently fixed to an axle, which is then rotated by the steering column. See

Figure 31 below.


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Figure 31: Wagon style steering mechanism

Steering Knuckle System:

This system is more complicated; however it also solves many of the problems of the Wagon wheeltype. The steering knuckle system consists of wheels mounted to “knuckles”, which are in turn mountedto an axle. These knuckles are then driven by a 4-bar linkage connected to the steering column, as shownin Figure 32. Because it is driven by a 4-bar linkage, this system is much more stable. Another advantageof being driven by a 4-bar linkage is that by adjusting the lengths of various bars, optimizations and

changes can be implemented (Steering Systems).

Figure 32: Knuckle steering system


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4.4.3 System Selection

Because of its many advantages, the steering knuckle system was employed in our Supermileagevehicle. The final product is similar to Figure 33.

Figure 33: A knuckle steering system implemented in vehicle

4.5 Rolling Resistance

Rolling resistance is a major inefficiency that occurs between the tires and the ground. For a cyclist,

rolling resistance can account for up to 80% of drag at speeds of 6mph and as much as 20% at speeds of25mph. Therefore, decreasing rolling resistance would make the Supermileage vehicle much moreefficient. When a tire holding up weight bulges against the ground it increases the contact area (SeeFigure 34) . This area is directly related to the amount of friction the tire feels from the ground. Tominimize the friction one needs to decrease this contact patch by investing in a thinner tire or increasingthe tire pressure.


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Figure 34: Contact area and rolling resistance

4.5.1 Testing and Calculations

There was no testing on different tires due to the high upfront costs of buying tires and lack of a testingfixture similar to Figure 35. Typically, tires are tested on a rolling drum while a known weight is presseddown on the tire. The drum rolls at a known speed and the torque required to keep the drum rollingequates to a rolling resistance coefficient.

Figure 35: Rolling resistance test fixture

To simplify, the team considered the power to propel the vehicle forwards as a function of the rollingresistance, weight and velocity. Thus with just a researched rolling resistance constant the team coulddetermine the power to overcome this drag using Equation 11, below.

P rr

= C rr

Nv Eqn. 11


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Where C rr is the rolling resistance coefficient, N is the weight on the tire and v is the velocity of thevehicle. Since the Supermileage vehicle is much heavier than a road bike, it was very important to notethe weight in these calculations.

4.5.2 Alternatives

Among bike tire enthusiasts, there is some rolling resistance data — but it is not common for a bike tirecompany to publish these numbers as they are dependent on too many factors: weight, tire pressure,temperature, speed...etc. However, as one can see in Table 3, rolling resistance coefficients for high-endtires are quite small, but when multiplied by weight and velocity the magnitude of the power loss due tothe rolling resistance can be upwards of 70 watts.

Table 3: Rolling resistances

Tires Crr

Veloflex Carbon 0.0049

Gommitalia Platinum 0.0053Vittoria Corsa Evo CX 0.0054

Vittoria Corsa Evo KX 0.0057

Continental Competition 0.0059

Many cyclists choose a larger diameter tire for its lower rolling resistance. As said before, the rollingresistance is a function of several variables. To simplify, the analysis only considered the diameter.Equation 12 relates the coefficient of rolling resistance to the diameter D of the tire and the amount ofvertical deflection z.

C rr = z

D Eqn. 12

Using this equation, tires from Table 3 have a vertical deflection of about 700-1000 micro-inches. Notethat this analysis assumes a constant deflection amongst tire options. Using the constant deflectionassumption and a 28-inch tire, the coefficient of rolling resistance becomes 0.0057 for a high-end tire.

4.5.3 Final Selection

There are hundreds of bike tires to choose from with differing coefficients of rolling resistance, price andsize. The order of magnitude calculations discussed in section 2.4 was used to determine which tire

diameter would optimize the aerodynamic drag and rolling drag. Figure 36, below, shows the power loss(in watts) of the combined drag and rolling resistances as a function of the tire diameter. An optimumdiameter was found using the following equations for power loss in the aerodynamic drag and rollingresistance.

Eqn. 13


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√ Eqn. 14 Eqn. 15

By taking the derivative of P resist with respect to D and setting it equal to zero, a minimum wasdetermined. The optimum tire diameter becomes:

Dopt = zW

C 1C d v2

ë

ù

û

ú

2/3

Eqn. 16

Plotting this for a few velocities between the required 15-25mph yielded Figure 36. For example, theoptimal tire diameter that minimizes the power losses due to aerodynamic drag and the rolling resistancefor the vehicle traveling at 20mph is about 24 inches. However, this poses an interesting dilemma:lowering the vehicle diameter also increases the rolling resistance coefficient. Ultimately the teamdecided that it was more important to reduce rolling resistance than aerodynamic drag given the vehicleoperating speeds. Using large diameter tires will provide excellent rolling at the cost of loweredaerodynamic performance. Again, this was justified given the SAE competition speed regulations (mustmaintain an average of between 15-25 mph). After these considerations, the team selected VelocityEscape 700c 32H Black MSW rims with Continental 22mm tubular tires. These tires have a maximuminternal pressure of 200 psi, about double what many bikes use.

Figure 36: Optimum tire diameters


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4.6 Electrical Subsystem

The SAE competition rules state that each vehicle must exhibit brake lights as well as three kill switches.Team Supermileage designed two internal circuits to connect the engine to the fuel injector, as well as thelights to the starter. All circuits will be fitted with appropriate fuses.

4.6.1 Engine and Fuel Injector Circuit

According to competition rules, each of the three kill switches must be able to stop the engine and anyfuel injection system. The difficulty of this circuit design comes in how each of the components shutsdown: the engine requires a closed circuit to stop; the fuel injector requires an open circuit to stop. Thecircuit shown in Figure 37 designed to comply with the rules.

Figure 37: Engine and fuel injector circuit diagram

Most of the wires were fit inside the frame. The circuit will use a 12V battery, firmly mounted behind thefirewall. The vehicle-wiring scheme can be seen in Figure 38, below. Colored wires help distinguishcircuits.

Figure 38: Engine and fuel injector vehicle circuit layout


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4.6.2 Brake Lights and Starter Circuit

The second circuit contained brake lights and the engine starter. Lights and engine starter both willrequire a momentary single pull single throw (SPST) switch to allow them to be turned on only when theyare being used. Figure 39 shows the circuit diagram. Figure 40 shows the vehicle circuit configuration.

Figure 39: Brake lights and engine starter circuit diagram

Figure 40: Brake lights and engine starter vehicle layout


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5 Vehicle Costs

5.1 Cost Estimation Development

5.1.1 Registration Costs

The registration costs for the SAE Supermileage® competition are unfortunately not cheap. Registrationcost $600, although this did include a “donated” engine.

Table 4: Registration costs

RegistrationItem Description Cost/Item Qty Total Cost

Registration Fee $ 600.00 1 $ 600.00

Sub Total $ 600.00

5.1.2 Body and Frame Costs

The body/frame portion of the budget was surprisingly cheap. The team purchased about $30 worth ofaluminum, a few shoulder bolts, and a few other miscellaneous parts. This brought the total spent on theBody/Frame to be $50. In addition, Calvin College donated about $10 worth of aluminum and brass,which the team used to make the axles for the front wheels. The team did all part fabrication and weldingthemselves in an effort to keep costs down.

Table 5: Body and frame costs

Body/FrameItem Description Cost/Item Qty Total Cost

Aluminum Channel (1.5"x1"x0.125") $ 1.80 14 $ 25.20Aluminum Tubing (1.5"x1.5"x0.125") $ 1.85 3 $ 5.55Shoulder Bolt $ 10.22 2 $ 20.44

Sub Total $ 51.19

5.1.3 Wheels/Brakes/Transmission

The wheels/brakes/transmission/steering aspect of the budget was a little pricier. As mentioned earlier,minimizing rolling resistance was a huge priority, and so our team was willing to spend heavily on wheelsand tubes to aid this minimization. Another pricy item in this category was the thermoplastic bearings.These were not cheap, but enabled us to save several pounds of weight.


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Table 6: Wheels/Brakes/Transmission/Steering Costs

Wheels/Brakes/Transmission/SteeringItem Description Cost/Item Qty Total CostFront: rims + spoking $ 140.00 2 $ 280.00McMaster Steering fasteners $ 9.81 1 $ 9.81McMaster Steering tie-rods $ 11.88 1 $ 11.88McMaster transmission sprocket $ 9.96 1 $ 9.96McMaster transmission keyed shaft $ 31.50 1 $ 31.50Comet: Al sprocket and hub $ 62.00 1 $ 62.00Rear wheel: (w/ Int. Hub) $ 248.00 1 $ 248.00Tubes $ 85.00 3 $ 255.00Thermoplastic Bearings $ 138.85 1 $ 138.85

Sub Total $ 1,047.00

5.1.4 Electrical Costs

The electrical costs were pretty reasonable. The taillights cost about $45, but otherwise most of the costcame from miscellaneous wires and switches.

Table 7: Electrical Costs

ElectricalItem Description Cost/Item Qty Total Cost

Mcmaster wire organizers $ 28.72 1 $ 28.72DPDT Switches $ 3.99 2 $ 7.98Lights $ 45.22 1 $ 45.22Lowes: 14gage wires $ 32.37 1 $ 32.37RadioShack: wires and connects $ 16.26 1 $ 16.26

Sub Total $ 130.55

5.1.5 Engine and Powertrain Costs

The Engine expenses stemmed mainly from the purchase of a fuel-injection kit. This cost the team$512. Other items purchased included fuel-lines and insulation to wrap the engine in. In addition, theteam received support from Baker Engineering in testing and modifying the engine. They allowed us torun our engine on a dynamometer and gave advice on how to best proceed with modifications and fuel-injection installation. This was estimated to be about $750 worth of time and help which BakerEngineering donated.


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Table 8: Engine and Powertrain Costs

Engine

Item Description Cost/Item Qty Total CostFuel Injection Kit $ 512.00 1 $ 512.00Nunica Marathon Engine Petrol $ 18.62 1 $ 18.62Gasket Material/Exhaust $ 35.00 1 $ 35.00Insulation $ 20.00 1 $ 20.00

Sub Total $ 585.62

5.1.6 Shell Costs

The Shell cost about $1,000 for Dacron material, epoxy, resin, and foam. This was laid up over a

Styrofoam plug in a “sandwich -core” manner to create the shell. The Styrofoam plug was donated byBetz Industries and is estimated to be valued at about $500.

Table 9: Shell Costs

ShellItem Description Cost/Item Qty Total CostBetz Styrofoam molds (donation) $ - 2 $ -Dacron Covering $ 6.85 10 $ 68.50Dacron Covering (reorder) $ 7.34 5 $ 36.70Vinyl Foam $ 29.85 7 $ 208.95Vinyl Foam (reorder) $ 34.93 2 $ 69.86Duratec StyroShield $ 133.27 1 $ 133.27FibRelease $ 33.61 2 $ 67.22MEKP Hardener $ 6.27 3 $ 18.81System West Epoxy $ 99.99 1 $ 99.99System West Epoxy (reorder) $ 39.99 1 $ 39.99Paint Brushes (Harbour Frieght) $ 15.30 1 $ 15.30Fields Fabric: layup fabric $ 2.97 10 $ 29.70System West Hardener $ 45.99 1 $ 45.99Mcmaster shell rubber strip seal $ 63.05 1 $ 63.05Sawhorse Materials $ 46.41 1 $ 46.41Lowe's Paint Supplies $ 42.45 1 $ 42.45Epoxy Pumps $ 14.99 1 $ 14.99

Sub Total $ 1,001.18


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5.1.7 Testing Equipment

Testing equipment included a load cell that had to be purchased for dynamometer testing and strain gagesthat were used in wind tunnel testing. This totaled about $400.

Table 10: Testing Equipment Costs

Testing EquipmentItem Description Cost/Item Qty Total CostBaker: Test Load Cell $ 374.76 1 $ 374.76Strain Gages $ 19.60 1 $ 19.60

Sub Total $ 394.36

5.1.8 Total Costs

Total monetary costs spent on this project totaled $3,809.90. Note that our team received a $300donation, which brought the total cost to the engineering department down to about $3,500. It is difficultto quantify donations of parts and time in financial terms, but it is estimated that without the donationsreceived, this vehicle would have cost around $5,000.

Because this vehicle is a one- time project, it is a little difficult to have a “production cost.” For the purposes of this project, production costs were assumed to take into account the cost of designing,constructing, and optimizing the vehicle. This total cost would then be exactly the same as shown above,with the addition of design and construction time. It is estimated that this project required at least 500hours per person. Therefore if we assume that each team member was paid $25/hour, the total cost of this

project was $125/hr. At this rate, the total cost of labor/design/construction works out to be $62,500, andtotal vehicle value equals $67,500.


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6 Conclusion

The above sections document the feasibility, design, and fabrication of a vehicle to compete in the SAESupermielage® completion by Team 6. Specific design solutions outlined above provide insight into thefollowing vehicle categories: aerodynamics, engine optimization, frame design, engine design, and powertransmission. These design solutions were selected in effort to minimize vehicle inefficiencies while alsomaintaining the SAE Supermileage® rules. Looking back, in addition to successfully implementing thesedesigns, Team 6 believes they have learned valuable team skills throughout this project. Team 6 hasgreatly enjoyed assessing and overcoming the many challenges that came their way throughout the year,and is looking forward to seeing how the vehicle holds up in competition!


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7 Acknowledgements

Many people offered technical assistance and gave advice toward this project. We would like toespecially thank the following people:

Professor Ned Nielson (Calvin College)

Professor Richard Dejong (Calvin College)

Professor Matthew Heun (Calvin College)

Phil Jasperse (Calvin College)

Briggs and Stratton

Ren Tubergen (Industrial Consultant)

Dave Jones (Steelcase)

Bryan Stratton (Intertek)

Evert Klomp (Kentwood Cycle)

Craig Overweg (Reliable Automation)

Jeff VanKuiten (Betz Foundry)

Mark Dorner (Baker Dorner)

Joe Flickweert (Supermileage 2011 team member)

In addition, we would also like to thank our families and friends for giving us support and encouragementin undertaking this project.


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8 References

"2012 SAE SUPERMILEAGE® RULES." SAE International . Web. 17 Nov. 2011.

.

Aleklett, Kjell, Mikael Hook, and Kristofer Jakobsson. "The Peak of the Oil Age." Energy Policy 38.3

(2010). Mar. 2010. Web. 17 Sept. 2011.

.

"Carburetor." Wikipedia, the Free Encyclopedia . Web. 09 Oct. 2011.

.

engel, unus A., Robert . Turner, and ohn M. Cimbala. Fundamentals of Thermal-fluid Sciences .

Boston: McGraw-Hill, 2008. Print.

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9 Appendices

9.1 Appendix A: Wind Tunnel Stress Calculations

Derivation for Equation 7:


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9.2 Appendix B: EES Order of Magnitude Calculations


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9.3 Appendix C: MathCAD Frame Calculations


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9.4 Appendix D: FEA Frame Simulations

1. M ain Beam Stress An alysis2. Rigidity Br acing for M ain Beams3. F ron t End Stress Analysis4. Roll Bar Stress An alysis and M ater ial Removal

1. M ain B eam Design.Calvin Supermileage2/15/12Selection: 1.5x1x1/8in Channel. Length = 66in

Beam Loading

Static Loads for one beam.Loads # of loads Subtotal weight / Beam

Point Shell 5.56 lbf 4 22.24 lbfPoint driver 45 lbf 1 45 lbfPoint engine 22.75 lbf 1 22.75 lbfDist driver 0.938 lbf/in 1 22.5 lbfDist overall 10/66 lbf/in 1 10 lbfAssumes vehicle weight of 110 lbf; driver weight of 135lbf.

Reality Check:Compare theoretical and algor results for a simple loading case. 100lbf applied in the center of the beam(33in).


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Theoretical deflection = 0.415in; Algor simulated deflection = 0.435 in.

Impact Force SimulationTo simulate the vehicle hitting a pothole, the drivers load is considered to be an impact force. The Impactforce is calculated using the energy method as described in Norton on page 108.

Impact Load Determination For Channel 1.5x1x1/8 in. Length = 66in.


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Deflections due to drivers static load.At point load, deflection =0.130in; distributed load, deflection range from 0.130in to 0.192in

“if the weight is dropped on a beam, the static deflection of the beam at the point of impact is used”(Norton P109 middle paragraph).

CASE 1: impact load height = ¼ inCASE 2: impact load height = 1 inCASE 3: Static Load

Case 1: I mpact L oadin g height = 0.25in


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Minimum factor of safety = 2.96 (impact load height = 1/4in)

Maximum deflection = 0.79in (impact load height = 1/4in)

Case 2: I mpact loadin g height = 1in


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Minimum factor of safety = 2.0 (impact load height = 1in)

Maximum deflection = 1.14in (impact load height = 1in)

Case 3: No I mpact loading, assume static loading.

Minimum factor of safety = 6.49 (static loading)


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Maximum deflection = 0.375in (static loading)

Case 4: Static L oading Un der Roll Bar Test

Minimum factor of safety = 2.86 (static loading)

Close up

Maximum deflection = 0.69in (static loading)


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2. Rigidity Bracing

Displacement in the horizontal direction. Loading: 1in impact. 30 degree, NO BRACING!

Displacement in the horizontal direction. Loading: 1in impact. 30 degree

Displacement in the horizontal direction. Loading: 1in impact. 30 degree, WITH 2 BRACING! (25,51in)

3. F ront End Stress AnalysisCalvin Supermileage2/15/12Selection: 1.5x1.5x1/8in Tube. Length = 20in


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Reactions for no impact loading (static) (Ra = 78.8lbf, Rb = 48.7lbf)

Max displacement magnitude = .0081in (static loading condition)

Minimum factor of safety = 204. Roll Bar Stress An alysis


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Roll bar with no material removed. Meshing example

Mesh Percent 100 70 40 20 10Max Stress(PSI)

1700 2700 4700 5700 6000

With material removed for weight.MODEL: LOTSTop beam stresses match models above, verifying the model.

Vertical 250 lbf load; overall


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Vertical 250 lbf load; bottom

Vertical 250 lbf load; side joint

S

sae supermielage

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