Formula SAE RacecarDriver AidsProject 05101

Ryan NewardHenry BergTim FalkiewiczNick LehnerAnthony MagagnoliDoug PayneJohn Schnurr

Table of Contents

1 INTRODUCTION.................................................................................................................................5

2 TEAM ORGANIZATION...................................................................................................................8

3 NEEDS ASSESSMENT......................................................................................................................10

3.1 Introduction....................................................................................................................................10

3.2 Driver Input....................................................................................................................................11

3.3 Electro-Pneumatic Shift System...................................................................................................12

3.4 Pneumatic Cylinder.......................................................................................................................12

3.5 Manifold and Solenoid Assembly.................................................................................................12

3.6 Gas Storage Tank...........................................................................................................................12

3.7 Electric Components......................................................................................................................13

4 CONCEPT DEVELOPMENT...........................................................................................................14

4.1 Possible Solutions...........................................................................................................................144.1.1 Turbocharging.............................................................................................................................144.1.2 Paddle Shifting............................................................................................................................144.1.3 Clutch Release Control................................................................................................................154.1.4 Traction Control..........................................................................................................................15

4.1.4.1 Brake Actuated Traction Control.......................................................................................154.1.4.2 Throttle Controlled Traction Control.................................................................................164.1.4.3 Fuel/Spark Controlled Traction Control............................................................................164.1.4.4 Dual Rev-Limiter Launch Control.....................................................................................16

4.1.5 Flat Shift......................................................................................................................................164.1.6 Automatic Up-shift......................................................................................................................17

4.2 Types of Shift Actuation................................................................................................................184.2.1 Mechanical Actuation.................................................................................................................184.2.2 Electric Solenoid Actuation........................................................................................................184.2.3 Hydraulic Actuation....................................................................................................................194.2.4 Pneumatic Actuation...................................................................................................................19

4.3 System Components.......................................................................................................................204.3.1 Cylinder Mounting Location.......................................................................................................204.3.2 Air System Components..............................................................................................................214.3.3 Driver Interaction........................................................................................................................224.3.4 System Monitoring......................................................................................................................24

5 FEASIBILITY.....................................................................................................................................26

6 ANALYSIS AND SYNTHESIS.........................................................................................................35

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6.1 Shift Number Calculations............................................................................................................35

6.2 Electrical Calculations...................................................................................................................386.2.1 Voltage Reduction for RPM Sensor............................................................................................386.2.2 Voltage Reduction for Control Board Power Supply..................................................................39

6.3 Valve Sizing....................................................................................................................................41

7 SPECIFICATIONS.............................................................................................................................46

7.1 System Specifications.....................................................................................................................46

7.2 Specifications for the Paddle System............................................................................................46

7.3 Specifications for the Pneumatic System.....................................................................................46

8 PRELIMINARY DESIGN.................................................................................................................47

8.1 Design Elements.............................................................................................................................47

8.2 Materials.........................................................................................................................................47

8.3 System Operation...........................................................................................................................488.3.1 Paddle/Button Shifting................................................................................................................49

8.4 Flow Charts....................................................................................................................................50

8.5 Flat Shifting....................................................................................................................................528.5.1 Automatic Up-Shifting................................................................................................................538.5.2 Two Stage RPM Limiter.............................................................................................................548.5.3 Current Gear Display..................................................................................................................558.5.4 Correct Shift Detection................................................................................................................568.5.5 Pneumatic System.......................................................................................................................578.5.6 Microprocessor Code and Pertinent Information........................................................................58

9 FUTURE PLANS................................................................................................................................60

9.1 Focus................................................................................................................................................60

9.2 Paddle Shifting...............................................................................................................................60

9.3 Flat Shift..........................................................................................................................................61

9.4 Automatic Up-shift.........................................................................................................................61

9.5 Launch Procedure..........................................................................................................................61

APPENDIX A - ABBREVIATIONS...........................................................................................................63

APPENDIX B – MICROPROCESSOR CODE.........................................................................................64

Appendix C - References................................................................................................................................69

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Table of Figures

Figure 1 – FSAE Competition Results................................................................................6Figure 2 – Steering Wheel Front.......................................................................................23Figure 3 – Steering Wheel Back........................................................................................24Figure 5 - Voltage Reduction Circuit................................................................................38Figure 6 - Control Board Power Supply............................................................................40Figure 7 - Valve Sizing......................................................................................................42Figure 8 - Graph Factor Fg................................................................................................43Figure 9 - Fsg Chart...........................................................................................................44Figure 10 - Ft Chart...........................................................................................................45Figure 11 - Complete System Schematic………………………………………………...48Figure 12 - System Flowchart……………………………………………………………50Figure 13 – Auto Up-shift Flowchart................................................................................51Figure 14 - Pneumatic System and Controls……………………………………………..56Figure 15 - Flat Shift System.............................................................................................53Figure 16 - Automatic Up-Shift.........................................................................................54Figure 17 - Two Stage Rev Limiter...................................................................................55Figure 18 - LED Gear Display...........................................................................................56Figure 19 - Pneumatic System...........................................................................................58

List of Tables

Table 1 – System Descriptions..........................................................................................27Table 2 – Feasibility of Different Systems........................................................................30Table 3 – Launch Control Feasibility................................................................................32Table 4 – Launch Procedure Feasibility............................................................................32

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1 Introduction

The Formula SAE is a design competition that challenges SAE student members

to design and build an open-wheel formula-style race car. The students must follow a

specific set of rules that governs the design and components of the car. However, these

rules are more a result of safety concerns than a restriction on advanced design.

Therefore it is up to the imagination, creativity and design skills of the students to come

up with the best car possible. The design of the car usually takes place over the period of

about a year and culminates with the entry into one or all of the three annual international

competitions. The three competitions are:

1. Formula SAE held in the United States

2. Formula Student held in the United Kingdom

3. Formula SAE Australasia held in Australia

The three competitions draw teams from all over the globe and may have as many as 140

teams competing against one other.

The idea of this competition is for the students to assume a manufacturing firm

has approached them to produce a prototype car for evaluation as a production item. The

target sales market for this car is assumed to be the weekend nonprofessional autocross

racer. As a result, the car must have very high performance characteristics in the areas of

speed, acceleration, braking, handling, safety and reliability. It must also be low in cost,

easy to maintain, and tunable for specific driver needs. Due to the fact that the target

market for this product is the general public, the car must also be aesthetically pleasing,

comfortable and use common parts. The manufacturing firm is looking to produce about

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four cars per day for a limited production run and the prototype vehicle should not exceed

$25,000. The goal of the design team should be to design and fabricate a prototype car

that meets all of these criteria. The final product will be compared against all other

designs to determine the best overall car.

The car will be judged based on its performance in a variety of both static and

dynamic events. These events include: technical inspection, cost, presentation,

engineering design, solo performance trails, and high performance track endurance. The

first event is the technical inspection. This is worth no points in the competition, but it is

required to determine whether the vehicle meets all the FSAE rules and requirements.

These rules are laid out in the respective year’s rule book that can be found online.

The cost event is comprised of two different parts. The first part is a written

report that the team must present to the Cost Judges prior to the competition. This report

must contain a variety of items ranging from a section explaining the bill of materials

with receipts and descriptions of the parts to process descriptions that explains any parts

that were created from scratch, or purchased and then modified. The second part of this

event is a discussion at the competition with the Cost Judges around the team’s vehicle.

This evaluates the team’s knowledge and ability to prepare accurate engineering and

manufacturing cost estimates. This event is used to teach the students the importance of

budget concerns that must be taken into account in any engineering exercise. It also

pushes students to learn and understand the techniques used to create any of the

components that the team decided to purchase instead of fabricate themselves.

The objective of the presentation event is to determine the team’s ability to

prepare and deliver a comprehensive business proposal that will convince the executives

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of a manufacturing firm to proceed with their design. The team must act as though they

are presenting to a room full of executives from all branches of the firm including

engineering, finance, marketing, and production, and thus they may not all be engineers.

The team must convince this group that the design that they have come up with is the

most desired by their target market of weekend nonprofessional autocross racers, and that

it can be profitably manufactured. Although the presentation must be about the actual car

brought to competition, the quality of the prototype itself has no influence on the score in

this event.

The design event is used to evaluate the team’s ability to use their engineering

design skills to meet the needs of the market. The team that can best illustrate their use

of first-rate engineering practices to meet the design goals and understanding of the

design by the team members will score the most points in this event. For this event, it is

preferred that the components used within the car are original, student designed parts.

These parts are evaluated on the design itself and on the application within the vehicle.

Any items that are incorporated into the car as finished components however are not

scored on their design, but instead only on the selection and integration of the component

into the car to maximize its performance.

The dynamic part of the competition is where the actual performance of the car is

tested and the engineering design and application are truly tested. The first event in the

dynamic part of the competition is the acceleration run. This event is used to determine

the acceleration of the car in a straight line on flat pavement. The car will accelerate

from a standing start to a distance of 75 m. It will begin 0.3 m behind the starting line

and the time does not begin until the front of the car crosses this line.

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The next dynamic event is the skid-pad. The objective of this event is to

determine the car’s cornering ability on a flat surface while making a constant-radius

turn. The basic layout of the skid-pad consists of a 3.0 m wide path of two circles of

15.25 m diameter in a figure eight pattern. The driver must enter the figure eight and

complete one lap on one of the circles to establish the turn, then after completing the first

lap, the second lap is timed. The driver must then repeat the same procedure on the

second half of the figure eight immediately following the first timed lap. The score is the

average of the two times with penalties assessed for knocking over cones or running off

course.

The autocross event is the true test of the vehicle’s ability to perform in all areas

of overall maneuverability and drivability such as cornering, acceleration, and braking,

without the hindrance of competing cars. The autocross course is made up of straights,

constant turns, hairpin turns, slaloms, and miscellaneous elements such as chicanes,

multiple turns, decreasing radius turns, etc. Average speeds through the course can be

expected to be around 45 km/h. The straights may be 60 m in length with hairpin turns at

the ends, or shorter 45 m straights with wide turns at the ends. The course is made using

cones with the minimum track width being 3.5 m. Penalties are assessed for any knocked

over cones, exit from the course, or missed slalom. The score for this event is based on

the time it takes for the car to complete the 0.805 km course with penalties assessed.

The final and most important of all the events in the competition is the endurance

and fuel economy tests. The endurance portion of this event is worth more overall points

in the competition compared to any other event by more than two fold. The endurance

event consists of the vehicle running through an autocross type course with an average

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speed of about 50 km/h and a top speed of approximately 105 km/h. The vehicle must

complete the 22 km heat without stopping, except at the midpoint to change drivers. The

final score for this event is based on the overall time with the addition of any penalties

that may have incurred. The fuel economy score is based on the average liters of fuel per

kilometer during the endurance event.

As can be seen by the point breakdown for each of the events throughout the

entire competition, the dynamic events are the most important to determine the team’s

overall placement. These dynamic events are a measure of the strength of the mesh

between the driver and the vehicle. A car that can out-perform anything else on the road

is useless of the driver cannot utilize its abilities. Similarly, a driver with exceptional

skills cannot maneuver around a track in a vehicle that will not respond to his inputs. It is

therefore critical that the interaction between the driver and his machine be as seamless as

possible so that the performance of both can be maximized.

As shown below in Figure 1, the FSAE team places lower in the rankings,

compared to their other scores, in the events that are very driver dependent. This is what

led to the decision to increase driver aids. It was evident that something needed to be

done so that the performance of the car could be increased by taking some of the

processes out of the driver’s hands and in turn automating them. It could then be possible

to design an automated system to give the best possible performance on a more consistent

basis.

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Placement In Each Event

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10

20

30

40

50

60

70

80

Cost Presentation Design Acceleration Skid Pad Autocross Endurance Overall

Event

Plac

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200220032004

Figure 1 – FSAE Competition Results

After discussing the need with the FSAE members it was found that one of the most

cumbersome operations for the driver to perform was to shift gears. It seems like a

simple task, but with unassisted, quick-ratio steering and in a racing situation, taking even

one hand off of the steering wheel makes controlling the car even more difficult. By

relocating the gear selector for the sequential transmission to the steering wheel itself, the

driver would have better control over the car’s steering because he would not have to

ever remove his hands from the wheel. By creating electric paddles and buttons on the

wheel, the driver can call his next gear and have it pneumatically actuated for him.

In addition to the improved performance by the driver as a result of this design,

other systems can be integrated that will allow for the interaction between the driver and

the car to be even smoother. A system that will do just that is one in which the engine

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can automatically be retarded in order to match the speed of the next higher gear without

the driver lifting his foot off the gas pedal. In addition, it is possible to take any driver

interaction with the shifter out of the equation and just have an automated system that

automatically up-shifts through the gears at prescribed optimal rpm levels in an event

such as the acceleration run.

Another very difficult task for the driver is “launching” the car, or accelerating the

car from a complete stop, in the most efficient manner. The cable-operated clutch is

extremely difficult to modulate. The low torque / high horsepower nature of the engine

creates a situation where the car either stalls or bogs (launching slowly with the engine

well below its optimal power range), or excessively spins its tires. The most effective

solution was determined to involve implementing a 2-step rev limiter. The standard rev

limiter remains at roughly 12,500 rpm, but the addition of a lower, tunable, limiter that

could be used to hold the engine at the ideal rpm in order to get a launch with a proper,

limited, amount of wheel spin, effectively getting the car moving faster sooner.

The increased speed and optimization of the shifting process, in combination with

the launch control procedure, will combine to decrease the overall time, especially in the

acceleration run. The additional control that the driver will possess while shifting will

give him better control of the car and increase his ability to be precise with his inputs for

the autocross and endurance events.

We will be improving the performance of the car while marginally increasing its cost

(< $500). By meeting the goals that we have set forth, the RIT FSAE team will improve

their competition results in both the dynamic and static categories.

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2 Team Organization

Senior Design team 05101 Formula SAE is made up of five mechanical engineers

and two electrical engineers. In the early stages of the project, each obstacle was tackled

as a team as opposed to splitting up the tasks and assigning smaller groups to solve the

problem. However, this method changed as it became clear that there were too many

aspects of this project for the team to solve together, due to the finite amount of time that

the team could all meet as a group. As a result, each member of the team started to

captain his own part of the design, and would report on his progress at the next meeting.

The work still remained very blended amongst the group members, but when there was a

concern about a certain design aspect, there was always a particular member of the team

that one could look to for an answer due to their work on that section.

As the team leader, Ryan Neward (ME) was in charge of most of the scheduling

and organizational issues. Some of the tasks that he would complete were such things as

making sure the entire project was running smoothly, and keeping things organized.

Henry Berg (EE) was the overseer of the project needs. He was in charge of

maintaining the direction of our project by keeping the needs in sight and making sure

that the team was always designing to meet these needs.

Doug Payne (ME) was the head of the controller portion of the design. He had

the most experience with the setup and integration of the controller into the design so that

the system would respond the way it was intended.

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Anthony Magagnoli (ME) was in charge of the steering wheel design. He has

extensive experience in the field of racing, and he is therefore knowledgeable about the

necessities of the desired mounting of paddles and buttons by the drivers.

John Schnurr (EE) oversaw the design of the electrical system. He was in charge

of making sure that we met our power requirements, and that each of our components

could be run off the battery power supply.

Tim Falkiewicz (ME) was in charge of coming up with the necessary equipment

for the pneumatic system. This entailed research and assessment of all the different

options for air tank sizes, pressures, regulators, and types of gas.

Nick Lehner (ME) oversaw the thermodynamic analysis that was critical to our

design. Almost all of our components could not be designed without the knowledge of

many different aspects of the system, which all funneled down to trying to answer the

issue of the number of shifts we could get from a different combination of inputs.

The chief tasks of each of the group members were just part of the work load that

the entire team had to complete. Each member was extensively involved in solving other

smaller engineering issues that needed to be answered to effectively complete our design.

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3 Needs Assessment

3.1 Introduction

The formula SAE driver aids project is subject to a few primary constraints that

serve as absolute necessitates. They include all of the following. First, shift actuation

must be via paddles and buttons. The system must automatically up-shift when the

function is active, it must also include a launch procedure for the acceleration event. The

completed system should not exceed one amp of total electrical system drain. Finally, a

minimum of 750 shifts is on one charge, but 2500 is preferred.

Secondary to the primary needs, this project is subject to a number of secondary

constraints that would greatly improve the usability and performance of the completed

system. The final attributes should include the following:

1. Affordable

2. Reliable

3. Innovative Technologically

4. Use for multiple disciplines

5. Uses limited external resources

6. Easily transferable from on design team to another

7. Improve targeted performance of car

8. Safe

9. Exclusive

10. High fatigue life

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11. Can be completed in a 6 month period

12. Involve some level of original design work

13. Desirable to the FSAE team

14. Usable by the FSAE team

15. Obeys FSAE rules

16. Light weight

17. Eliminates possibilities of driver error

18. Intuitive to use

Moreover, this design will be further enhanced if the technological attributes

place the team in the top three in overall team rankings in competition. This technology

should be exclusive to the RIT FSAE team.

3.2 Driver Input

This project has been defined by a few driver input requirements. They include

enable switches for both automatic up-shift and launch control. Additionally, the driver

needs both paddle and button shift actuation methods, along with a gear selection

indicator. This indicator will be in the form of a row of LEDs corresponding to each gear,

neutral through fifth. The current sixth gear is not used in competition. For future

designs, first gear will be eliminated and the current sixth gear will now be fifth gear. The

final drive ratio will be adjusted to compensate for the corresponding change in the gear

ratios.

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3.3 Electro-Pneumatic Shift System

The Electro-Pneumatic Shift System is a system which upon closing a switch

(paddle or button) the microprocessor will interpret the signal generated and subsequently

generate a signal to initiate a short release of compressed gas which serves as the

propellant to open a pneumatic ram directly connected to the transmission input shaft.

3.4 Pneumatic Cylinder

The pneumatic cylinder must generate a force greater than 20lbs at a 1.6 inch

offset from the transmission input shaft. It must be a double acting design, which will

allow powered extension as well as retraction using a single assembly.

3.5 Manifold and Solenoid Assembly

This assembly must have a three position, four way operation. This configuration

will allow for both full extension and retraction without blockage on the exhaust side of

the double acting valve; moreover, this will also allow for an inactive position that will

not restrict movement if the manual override must be used. This assembly must also not

push the cumulative power consumption above the maximum of one amp. The solenoid

must be powered by 12VDC and be able to handle a maximum pressure of 150psi. In

addition the solenoid must be operable between 20ºF and 180ºF.

3.6 Gas Storage Tank

This electro-pneumatic system will be ultimately powered by a gas, argon or high

pressure air, stored in a composite-wrapped tank. The tank should be as light as possible,

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with the ability to contain up to 4500 psi and with an internal volume of 44 cubic inches

(approximately 1.5 Liters).

3.7 Electric Components

Immediately prior to shift actuation, both spark and fuel need to be restricted so

that a ‘flat shift’ can be preformed. Flat shift is a term which describes the event where

the engine speed is retarded, eliminating the need for the driver to lift off of the

accelerator while shifting. This function will allow for a faster and more accurate shift

when compared to conventional means where the driver must lift off of the accelerator.

The microcontroller, which will serve as the intelligent control, must not push the

cumulative power draw above one amp. The controller must also be able to use both

input and output signals to control both electrical input as well as output requirements.

The controller must also run a program that is intuitive to modify and execute. In

addition the microprocessor subsystem must be able to interface with the high current and

voltage ignition and fuel systems of the car. Along with the fuel and spark subsystems,

the microprocessor needs an input from the transmission shift drum in order to confirm

an accurate shift has occurred.

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4 Concept Development

4.1 Possible Solutions

Many different types of driver aids were considered when evaluating the Formula

SAE senior design project. The sponsor submitted a plethora of problems with the car,

including touchy throttle control caused by the barrel throttle used, seating position,

launching traction, and loss of steering control when the driver removes his hand from the

steering wheel to shift. A number of systems were looked at which would be designed to

alleviate these problems and thus make the car faster. Many avenues were investigated,

including the following options: turbocharging the motor, a paddle shift system, a “Formula

One” style clutch release control, traction control, launch control, flat shift, and automatic

up-shift.

4.1.1 Turbocharging

It was thought that turbocharging the motor might aid the driver in low-speed throttle

modulation because of the inherent lag of the system. It was, however, decided that such a

system might make the car more difficult to control as the boost “comes on,” not to mention

the extreme complexity and difficulty in designing and testing such a system put it well

beyond the scope of the project.

4.1.2 Paddle Shifting

As the paddle shift system was investigated, it became apparent that it would be very

beneficial to the driver. This can be evidenced in the large number of other vehicles that are

now using such a system. It is becoming very common in racing cars, as well as street-

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oriented sports cars. The sponsor also put paddle shifters and a launch/traction aid on top of

their priority list. This, along with the feasibility assessment, were reasons to focus on those

two items.

4.1.3 Clutch Release Control

The clutch release control does just that: for acceleration event, it would control the

release of the clutch in order to keep wheel spin at an optimum level. It would avoid bogging

the motor down, or spinning the tires too much and wasting time. It was decided that such a

system would be extremely difficult to tune properly, and might lead to reliability problems

with the conventional operation of the clutch. It was deliberated that a launch control or

traction control system would be simpler to set up, and more reliable.

4.1.4 Traction Control

There are various ways to actuate a traction control system. Brake actuated traction

control, throttle controlled traction control, fuel/spark controlled traction control, and a dual

rev-limit launch control were investigated.

4.1.4.1 Brake Actuated Traction Control

The brake controlled system would require a separate ABS-style pump, which is

technology that is not currently on the car. It would also be extremely heavy, and possibly

provide rules conflicts because there needs to be a direct connection between the brake pedal

and the brakes, not to mention the extreme potential cost and the great amount of time that

tuning and perfecting it would require. This idea was eliminated because it was not at all

feasible.

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4.1.4.2 Throttle Controlled Traction Control

A throttle controlled system is not allowed in the rules, as the throttle must be directly

connected to the throttle pedal. Drive by wire is not allowed. It would also be potentially

expensive and difficult to tune properly.

4.1.4.3 Fuel/Spark Controlled Traction Control

The fuel/spark controlled system seemed to be the most viable, and slightly easier to

tune. Unfortunately, in the interest of time, simplicity and cost, it was decided to use a dual-

rev limit launch control system.

4.1.4.4 Dual Rev-Limiter Launch Control

The dual rev-limiter system is very simple and reliable. When activated, a second rev

limiter is enabled. This limits the engine from revving higher than a specific level, which is

determined to be the optimal launch RPM to gain the best traction. The engine’s control unit,

Autronic, already has this capability. It is much simpler to set up and test than any of the

other systems, while still being very effective

4.1.5 Flat Shift

A flat shift system is extremely useful (almost necessary) with a paddle shift system.

Flat shift momentarily retards the engine when a shift is called for, eliminating the need for

the driver to lift his foot off the gas pedal. This makes for faster shifts, and is easier than

trying to time foot movement with a press of a paddle. Using Autronic to control this is

possible, but after talking to the FSAE members it was decided that a separate system would

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provide more flexibility in tuning, as well as being simpler. Autronic requires that the driver

be at full throttle for the system to be active. The sponsor’s drivers sometimes have to up-

shift while turning, and not at full throttle. Instead of trying to devise a way to “trick”

Autronic into thinking that the driver is at full throttle at all times, a separate system would

allow for flat shift at every throttle position, as well as very flexible tuning. It would also

allow for more freedom with the timing and duration of the retardation of the engine. The

system will cut the common positive to the fuel injectors to eliminate the possibility of

detonation, or dumping unburned fuel into the exhaust, as well as cutting the negative to the

coils to cut spark to make sure that there is not a delay in the system caused by leftover gas in

the combustion chamber.

4.1.6 Automatic Up-shift

The sponsor specified automatic up-shift as a very important feature of the paddle

shift system. The automatic up-shift feature will be controlled by the same controller as

the other systems. The controller will read an output signal from the tachometer. When

the engine reaches the predetermined RPM level, the controller will send a signal for the

system to automatically perform an upshft. This will ensure that every shift occurs at the

perfect RPM for maximum acceleration, and should yield faster, as well as more

consistent acceleration times. The typical acceleration run lasts for less than five seconds,

so even a very small decrease in time could potentially yield a great increase in points

earned.

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4.2 Types of Shift Actuation

Once the type of launch aid was chosen and the use of paddle shifters were selected,

options for how a shift would actually be performed were explored. Four possible solutions

for actuation were considered: purely mechanical, purely electric, electro-hydraulic, and

electro-pneumatic.

4.2.1 Mechanical Actuation

The mechanical system, which would use linkages from a hinged set of paddles on

the steering column, was deemed to be a very promising solution. If properly designed, it

would be mechanically robust, as well as very reliable, with no electrical or other types of

connections to fail. It would also have an infinite life and have no drain on any other of the

car’s systems. Unfortunately this type of system had to be eliminated because it did not meet

one of the sponsor’s key priorities: having automatic up-shift capability. Automatic up-shift

can be very beneficial in the acceleration event because it ensures that each shift is performed

at exactly the perfect RPM for maximum acceleration, and that each shift will be performed

extremely quickly, saving time. Automatic up-shift, however, requires some sort of actuation

that does not involve the driver. The mechanical linkage system does not allow for this, and

thus had to be eliminated.

4.2.2 Electric Solenoid Actuation

The purely electric system was the next avenue that was explored. It looked to be

very promising because it does not involve storing a compressed gas or fluid on the vehicle,

and in theory it is has infinite life. As it was investigated further, it was found that the

electrical system from the Honda CBR 600 F3 motor is operating very close to its maximum

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current capacity as it comes from the factory. The system already has to power many

elements that it was not designed to power, such as a fan, ECU, and fuel injectors. Increasing

the output of the alternator was investigated, but it was soon realized that this would be

beyond the scope of the project. With the current electrical setup, the whole system would be

required to operate at one amp of current or less. The solenoids required for the electrical

system would require large amounts of current, which would mean that the system could not

operate under this limit. The system could not be used for extended periods of time without

draining the battery. The solenoids required would also be very heavy, and larger than had

first anticipated. Weight and packaging space are very large concerns with the Formula car.

Although it looked promising at first, the electrical system was thus eliminated.

4.2.3 Hydraulic Actuation

The electro-hydraulic system was deemed to be too complicated and heavy. The

main problem would be powering the hydraulic pump. It would either have to be run off the

engine, which robs it of horsepower and is very complicated, or electrically, which would

bring the recurring problem of requiring more current than is provided. If the system were to

fail and leak, it would cause a large mess, as well as a fire hazard. This eliminated the

hydraulic system.

4.2.4 Pneumatic Actuation

This left the electro-pneumatic system. The solenoids for the pneumatic cylinders

require very little current for their actuation (about 0.38 amps), and the rest of the system is

powered by air pressure contained in a bottle. This does not take power or current away from

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any other system on the car, and is thus autonomous. The cylinders are actuated by electric

solenoids, which allows for the automatic up-shift feature that is very important to the

sponsor. If a regulator pressure of 100 psi is used, cylinders capable of creating the required

force to shift the transmission are not very large, and thus easy to package. The major

hindrance of the pneumatic system is that it has a finite life. The vehicle can only shift until

the tank runs out of sufficient air pressure. The use of an on-board air compressor was

investigated, but it would add weight, and one could not be found that would operate at less

than the 1 amp current limitation. The sponsor specified that it wanted to see a minimum of

750 shifts, but would prefer to get at least 2500. After some careful calculation, it was

determined that it would be possible to achieve numbers higher than 2500 shifts with a

reasonably sized tank, at pressures that could be contained and filled without any large

inconvenience. The sponsor said that space could be found in the car to locate the bottle, so

this system was chosen.

4.3 System Components

4.3.1 Cylinder Mounting Location

Various cylinder mounting locations were investigated. Using cables and mounting

the cylinders remotely was immediately eliminated. Cables stretch over time, which could

eventually lead to the system not operating. This would be very detrimental to competition

results. Mounting the cylinder to the existing shift linkage was also investigated, but it was

determined that it would be the easiest in terms of packaging to mount the cylinder directly to

the shift shaft. This would also eliminate any possible friction loss through the joints in the

linkages. It would also allow for a very short lever arm of 1.6 inches, and thus a cylinder with

24

a fairly short stroke. This would mean that less air would be required for each shift and that

each tank of air could provide more shifts. The bottle will be located somewhere towards the

rear of the car, so this would also provide for the shortest length of air lines and thus the

smallest amount of loss through the system. The system will be designed so that the

conventional shifter mechanism can be retained, at least for the duration of testing. This will

ensure that if there is any sort of failure in the system (loss of air pressure, electrical failure,

etc), the car can still be shifted.

4.3.2 Air System Components

Besides the paddles and controller, the pneumatic system requires the following

components: tank, regulator, cylinder, and solenoid. A carbon or Kevlar-wrapped tank is

going to be used for weight considerations. Tanks are available that hold considerable

amounts of pressure. This should allow the tank to be significantly smaller. The size and

construction of the tank (and thus its maximum pressure capability) has a great impact on the

price of the tank. A tank must be chosen that has the best compromise between shift

capability and cost. A regulator is required to keep the amount of pressure going to the

cylinder consistent. An adjustable pressure regulator was chosen for initial development,

with the assumption that tuning would start at a pressure of 100 psi. Most of the air cylinders

have specifications given for a 100 psi operating pressure. This would also yield a decent

margin of safety to tune with before the maximum solenoid pressure of 150 psi is reached.

This should also make analysis more accurate because we know that the specs given will

hold true at this operating pressure. With the given lever arm of 1.6” on the shift shaft, a 100

psi operating pressure would yield 5/8” as a necessary cylinder bore to provide more than the

25

necessary shift force in both directions. This is a good size for packaging reasons. It was

decided to keep the lever arm length on the shift shaft that came from the factory. This allows

for tighter packaging, and makes it easier to retain the existing arm for use with the existing

shift linkage system. The cylinder will have to be a double acting cylinder as it needs to

control up, and downshifts. The solenoid controls the flow of the air. A four-way, three-

position solenoid will be necessary to allow for the cylinder to have up-shift, downshift and

rest positions. It also needs to have an open center. This will keep the cylinder from being

locked in position when the system is not active. A closed center would prevent the

conventional shifter from operating properly.

4.3.3 Driver Interaction

Once the type of system was chosen, it was important to consider the driver’s

interaction with the system. The group considered various avenues for ways to actuate the

shift without the driver removing his hands from the steering wheel. After investigating

many types of motorsport and production applications, three possible ways of activating a

shift without removing one’s hands from the steering wheel were examined: buttons

mounted on the face of the steering wheel, paddles mounted on the back of the steering

wheel that rotate with the wheel, or fixed paddles mounted to the steering column. The

sponsor prefers buttons and some sort of paddles. Different drivers have different

preferences, so this would meet the needs of everyone. It was decided that the buttons

would be mounted slightly inward on the spokes of the steering wheel so that they could

be easily reached by the driver’s thumbs, but would not be accidentally engaged during

sharp turning maneuvers (Figure 2).

26

Figure 2 – Steering Wheel Front

Switches for the automatic up-shift and launch control would be mounted below these for

ease of activation during competition. Of the two choices of paddles, steering wheel

mounted paddles were chosen. Paddles mounted to the steering column do not rotate with

the steering wheel. The autocross courses that the FSAE car races on are very tight and

often encompass quick back and forth turns. If the paddles were mounted to the column,

they would have to be very large so that they would still be in reach of the driver’s hands

during a sharp turn. Paddles mounted to the steering wheel can be much smaller because

they can be placed such that they are always in the correct position relative to the driver’s

hands. Also, because there would already be wires run to the buttons, it would be simpler

to tie these wires in to paddles mounted on the wheel and have a single connection to the

vehicle (the steering wheel must be quickly removable because of safety and the FSAE

rules). The best sizing/placement of the paddles was then investigated. It was found that

smaller paddles mounted further inward on the wheel would be best. This would require

the driver to remove fewer fingers to shift, and would allow most of the hand to remain

wrapped around the wheel at all times (Figure 3).

27Figure 1

Figure 3 – Steering Wheel Back

As per the industry “standard,” the left paddle will be used for downshifts, and the right

for up-shifts.

4.3.4 System Monitoring

One of the inherent problems with the shifting of the motorcycle transmission

used (and its lack of synchronizers), is that sometimes when a shift is asked for, the next

sequential gear does not engage and the transmission remains in the current gear. This

can be felt by the driver currently with the existing shift lever, but with a paddle shift

system, it might take the driver longer to react to such a problem. This would obviously

cause a loss of time, so some sort of countermeasure was necessary. It was decided that a

rotary potentiometer would be mounted to the shift drum, which rotates a set amount for

each gear change. A small hole would be drilled in the side of the transmission case, to

allow for the potentiometer to “know” how much the drum has rotated. If a shift is asked

for, and the system does not detect enough rotation, it will automatically retry the shift,

up to five times. This could also be used to keep the driver from trying to up-shift or

28

downshift when in the highest (sixth) or lowest gear (Neutral), respectively. The signal

from the sensor can also be used with a gear indicator on the dashboard to help the driver

keep track of what gear that he is in. An indicator on the steering wheel was considered,

but rapid steering wheel movements would make it hard to read. Unlike the initial plans

shown in Figure 1, it was decided that it will be placed on the dashboard or front roll

hoop, along with indicator lights for neutral, launch control, and automatic up-shift.

29

5 Feasibility

To begin the process of determining which driver aids to add to the car, the team

met with the sponsor to discuss current issues associated with driving the car and what

driver aids might help these issues. The three biggest issues with the car are: having to

move the driver’s hands away from the wheel to shift gears, difficulty launching the car

without spinning the tires for the acceleration run, and the seating position relative to the

wheel being uncomfortable for some drivers. There is not much that can be done about

the seating position, as the frame and seat mounting is designed by the sponsor.

Currently the car has a standard sequential gear shift lever mounted to the right of the

driver. Since the car takes a lot of force to steer, it is very difficult to hold the wheel and

shift in the middle of a turn. In addition, since it is manual shift, the driver may not hit

the optimal shift points in the acceleration run since it only lasts about five seconds.

Shifting at the correct time has a big impact on the acceleration time. The way the engine

intake is set up, the throttle is very sensitive when the car is at a standstill. A small

amount of pedal travel opens the throttle a large amount. This makes it very difficult to

get the exact throttle position so that the tires are at the optimal slip condition. If the limit

is exceeded, the tires spin and traction is lost. If the throttle is not pressed enough, the

engine is not operating at its peak and the car won’t accelerate as quickly.

After this meeting, the team began researching existing systems to get ideas to

resolve these issues. The team looked at various alternatives to make shifting gears

easier: mechanical linkages, push button electrical, push button hydraulic and push button

pneumatic. Methods to aid in throttle control were also explored: using a turbo on the

30

motor to limit the low end torque but increase horsepower as the RPM increase, launch

control and Formula One style launch control where the clutch is held at a position just

before it slips. In addition to this, a flat shift system was considered where the gearbox

can be shifted to a higher gear without lifting off the throttle and also traction control to

limit wheel spin while the car is at speed.

At the next meeting, ideas were shared along with their operation. Any systems

that were illegal due to rules were eliminated. Because there were so many options and

things to consider, a more organized way to decide which system would be the most

beneficial was needed. A feasibility matrix was constructed for the systems being looked

at. Table 1 describes the systems being looked at.

Table 1 – System Descriptions

The next step in constructing the matrix was to come up with criteria used to evaluate the

different systems. The first thing to consider was being able to complete this project

within the allotted time period. The team needed to ensure all the resources were in place

to complete this project. These included: enough time to develop the system and build it,

31

enough money to purchase all the components and team members with the skills to do the

work that the system will require in the allotted time.

The next thing considered was if it will actually work on the car. The main

concern was that the electrical system was limited to one amp. Additionally, the system

must be able to last for the competition and must be durable and reliable so that the

system does not fail. Finite life is primarily a concern with the electro pneumatic system

where an air tank is used and the system must be refilled when the air runs out. The

system must be durable to withstand the high vibration that is produced by the engine and

the bumps in the road transferred through the stiff suspension. Also, it must be reliable

so that it does not break down. Since the endurance portion of the competition is worth

the greatest percentage of points, finishing position drops significantly when the car

cannot finish the race.

The usefulness of the system must also be considered. Since certain systems like

electric shifting and flat shift go well together, paired systems were examined.

Innovation is what the Formula SAE competition is all about, so this is highly valued by

the sponsor. Judges look for new technology and it can earn the team valuable points.

Along with this is replacing an existing part with something new and better. It is very

important that the system be easily integrated into the car and driver. Since the

competition course is very tight, the system must be easy to use so that the driver does

not have to struggle to operate the system while trying to navigate the course. In case

something should break down, the system must be easily repairable so that the team can

return to the competition if the system fails. Also, the car needs to still function if the

system fails or it must use another system as a backup, such as the existing gear shift

32

lever. Ultimately, the sponsor is looking for a system that will make the car faster and

easier to drive. If the system does not fulfill these objectives, it will not have any value.

The last category to be looked at is other miscellaneous considerations for the

system. The sponsor highly values appearance and has a reputation of having a very

nicely built and put together car. Weight is also an important consideration since

lowering the weight increases acceleration and cornering speeds. Since the car is so

small, there is not much room to spare making packaging a concern. The system must be

able to fit in the small confines of the frame. Last, but most importantly, the system must

be 100% safe. The car is driven with corner workers and spectators in close proximity.

The system cannot at any time compromise the safety of anybody near the car.

The mechanical system was chosen as the baseline and given a three in each

category. The team went through each of the questions for all of the other systems and

rated them from one through five. A one meant that the given system was much worse

than the baseline mechanical system, a three means that it is equal to the baseline

mechanical system, and a five means that it is much better than the mechanical system.

The scores were totaled and the highest total indicates the best system. Table 2 shows the

feasibility matrix that was constructed.

33

FeasibilityCriteria Mechanical Electric Electro

HydraulicElectro Pneumatic

Turbo Motor

Launch Control F-1 Flat

ShiftTraction Control

Time Frame 3 3 2 2 1 3 3 3 3

Affordable 3 2 1 2 1 3 3 4 3

Sufficient Skills 3 3 2 2 1 3 3 4 3

Will it require too much current 3 1 2 2 3 2 3 2 2

Finite Life 3 3 3 2 3 3 3 3 3

Reliable 3 3 2 2 2 4 2 5 4

Robust (Durable) 3 2 2 2 3 4 4 4 2

Can be combined with another technology

3 5 5 5 3 4 3 5 4

Technologically advanced 3 4 5 5 5 4 5 2 4

Simplicity for driver 3 3 3 3 5 3 2 5 5

Replace an existing part 3 3 3 3 1 1 1 1 1

Ease of replacement 3 3 1 2 1 3 3 3 2

Make the car faster 3 3 3 3 4 5 5 4 4

Appearance 3 4 2 2 2 4 4 3 3

Weight 3 4 1 2 1 5 3 5 4Safety 3 3 2 3 2 4 3 4 5Packaging 3 5 1 2 2 5 3 5 5Totals 51 54 40 44 40 60 53 62 57Average 3 3.18 2.35 2.59 2.35 3.53 3.12 3.65 3.35

Table 2 – Feasibility of Different Systems

As shown in the matrix, flat shift scored the highest; launch control was next,

followed by traction control and electric shifting. The sponsor reviewed the results to

ensure they agreed with them and to evaluate their needs and wants. They came back

with a priority list based on the findings and what they are looking for. Their prioritized

list was the following:

34

1. Shift the gearbox without the driver removing hands from the steering wheel

without using a completely electrical system.

2. System for the above must have an electrical output to actuate Autronic’s

(engine control unit) flat shift.

3. Automatic up-shift.

4. Launch procedure for acceleration run.

Going back to the feasibility matrix in table 2, since the sponsor wanted a method to shift

gears that didn’t use electricity exclusively, the team was left with a purely mechanical

system, electro hydraulic and electro pneumatic. Although the mechanical system had

the most points in the feasibility matrix, the team chose to pursue the electro pneumatic

approach because it is impossible to have automatic up-shift with a purely mechanical

system. It also scored higher than the hydraulic system due to complications involved

with using a hydraulic pump and concerns of hydraulic fluid leaking onto the tires,

spinning the car and preventing the car from continuing, which is a huge safety concern.

The major concern with the electro pneumatic system is the fact that it has a finite life.

That is something that must be compensated for by the size of the tank, the gas that is

used and the pressure in the tank. Our sponsor is aware of this limitation and gave us a

bottom limit of 750 shifts per tank so that the tank will last long enough for the 22

kilometer endurance run. Twenty five hundred shifts per tank is much preferred so that

the tank can last throughout the entire competition without needing to be refilled.

For the launch procedure, a separate feasibility matrix was created to evaluate our

options for launch control. See table 3:

35

*Note: Drive by wire does not conform to rules.Table 3 – Launch Control Feasibility

The options being evaluated are summarized in table 4.

Table 4 – Launch Procedure Feasibility

The two step rev limiter was used as a baseline to evaluate the different options,

and each system was compared to the two step rev limiter for each feasibility criteria.

36

Many of the questions used for this analysis are the same questions that were used in the

first feasibility assessment. The only question that was added dealt with existing

hardware. This was added to take into account sensors and equipment that was already

on the car and being used. This helps in the number of parts that have to be purchased

and keeps the cost of the system down if the necessary components are already in place.

According to table 3, the two step rev limiter is the best option. The sponsor

agreed that this is the best system, but emphasized that it is the lowest priority and the

team should focus on the other three aspects of the project first.

Since a pneumatic method to shift the car is being used, another decision was the

gas to be used. Since the rules state that the gas must be nonflammable, our options were

rather limited. Carbon dioxide (CO2) and high pressure air (HPA) were examined

because there are numerous tanks and associated hardware that use these gases in both

SCUBA diving and paintball applications. The sponsor also suggested looking into

argon because they have an argon tank in the shop for welding and they also take an

argon tank with them to competitions. Since there are only three options, a simple

pro/con analysis was used to evaluate each gas.

CO2 was eliminated right away due to numerous problems associated with CO2

being a liquid when it is compressed. The liquid can leak out of the tank and into the

internals, clogging up lines. It also gives you very inconsistent outlet pressures because

the temperature varies depending on how fast the tank is opened. Additionally, CO2

freezes below 50 degrees Fahrenheit when it goes from high to low pressure causing ice

to get into the lines and other parts in the system. Often the car runs when the

temperature is below this, so the system must be able to work at these temperatures.

37

HPA a much better alternative to CO2 since it is more consistent across the temperature

range, cleaner than CO2 and is a gas at all temperatures and pressures it will be exposed

to. The downside for HPA is that it must be filled at a SCUBA shop or paintball shop.

HPA filling stations cost upwards of $1000, which is not within the budget for this

project. Since the Formula SAE competition is often run where there are not facilities

available to fill the tanks, they must have a tank large enough to hold enough air to last

the competition or bring spare tanks with them, which adds to the cost. The third

alternative, argon, has the same characteristics and will operate the same as HPA. The

downside for argon is that the weld tanks that it will be obtained from can only be filled

to a maximum pressures 2200 p.s.i. To make a decision on what gas to use, the tradeoff

between the size of the tank, the number of shifts that can be obtained from that tank at

the given pressure and the cost of the tank will have to be evaluated in more detail. Since

the sponsor always has argon available, it is much preferred, but it must be able to supply

a minimum of 750 shifts per tank for it to be a viable solution.

38

6 Analysis and Synthesis

6.1 Shift Number Calculations

To determine the capacity that will be needed for the tank to have, a spreadsheet

was created that would take into account the regulated pressure, pneumatic cylinder, type

of gas, force applied by the cylinder, and every conceivable variable in order to predict

how many shifts can be expected out of one tank full of gas. The user inputs the

following parameters of the pneumatic system into the spreadsheet: tank volume,

maximum tank pressure, regulator pressure, cylinder dimensions, dimensions of the air

line from the solenoid to the cylinder, the force required to shift, ambient conditions

(temperature and atmospheric pressure) and the type of gas. The spreadsheet converts all

of the values, which are inputted in English units to Metric, and converts the pressures

and temperatures to absolute values for use in the calculations (1), (2), (3). See Appendix

A for abbreviations.

1

2

3

The minimum regulator pressure required and the amount of shift force created with the

given setup are calculated as a check to ensure that the system will provide sufficient

force to shift the transmission (4), (5).

4

39

5

The ideal gas equation is used to solve for the mass of the chosen gas that will be

contained in the tank at the given conditions (6).

6

This mass is the amount of the gas that the system has to work with. The mass of air in

the tank at the regulator pressure (7) must be subtracted from this mass (8).

7

8

The air below regulator pressure can not be used, as it does not provide enough force to

actuate a shift (the regulator keeps this gas from leaving the air tank). This gives the total

mass of gas that is available to be used in shifting the transmission. The volume of gas

that is in the cylinder in its rest, and actuated positions (pos 1 and pos 2, respectively) are

calculated, and the volume of air in the air lines is added to both of these (9-16).

9

10

11

12

13

40

14

15

16

The volume in the line is necessary, because this volume must be pressurized with each

shift and returns to atmospheric pressure as the air exits the cylinder. The mass of gas in

the cylinder and line at atmospheric pressure when it is at position one is then calculated

(17).

17

This is used to calculate the mass of air in the cylinder and line at this position when it is

at the regulator pressure (18), which is in turn used to calculate the mass of air used with

each shift.

18

This is the mass of air contained in the cylinder and line when it is at position two at

regulator pressure, minus the mass of air in the cylinder and line at position one, and

atmospheric pressure (19-20).

19

20

41

This determines the mass of air that is taken from the tank with each shift. The amount of

useable mass of the gas is divided by this number to give the number of shifts that the

system can perform (21).

21

6.2 Electrical Calculations

6.2.1 Voltage Reduction for RPM Sensor

In order to implement the automatic up-shift system, the controller must receive

input from the cars RPM sensor. This sensor outputs a 12V square wave with a

frequency that is proportional to the RPM of the engine. The controller can only handle

inputs less than or equal to +5V. This requires that a circuit be designed to reduce the

sensor output to a maximum voltage of +5V.

Figure 5 - Voltage Reduction Circuit

42

There is a limited amount of current available for this project so the current drawn by this

circuit will be set to 2mA.

22

23

24

25

To provide the controller with the correct voltage, the circuit shown in figure 5 will be

constructed using resistor values of R1 = 3500 Ω and R2 = 2500 Ω.

6.2.2 Voltage Reduction for Control Board Power Supply

The controller being used for this system has a power supply voltage range of +7V to

+9V. The power supply available from the car is +12V. The circuit shown in figure 6

will be adjusted to supply the correct voltage.

43

Figure 6 - Control Board Power Supply

The maximum current the board can handle is 300mA. The current I2 will be set to this

number.

26

27

28

Set R2 = 100Ω

R1 = 7.7Ω

44

Total current drawn by this circuit:

ITotal = 390mA

To produce the required output voltage, the circuit shown in figure 6 will have the

following resistor values R1 = 7.7Ω and R2 = 100Ω.

6.3 Valve Sizing

The proper valve size for the solenoid can be calculated using the formula

provided in the ASCO Engineering Information reference. The importance of proper

sizing for the solenoid is to make sure that the valve is performing at its maximum level,

and also to avoid unnecessary costs.

The Cv method of valve sizing reduces all the variables to a common denominator

know as the Flow Coefficient.

(29)

Once this coefficient is found, it is then possible to find the proper valve size

using the table in Figure 7. This table is based on the ASCO designs of inline globe type

valves.

45

Figure 7 - Valve Sizing

For air the formula used to calculate Cv is:

(30)

where: SCFH is the air flow rate in standard cubic feet per hour. Fg is a constant found

using the graph in Figure 8. Using this graph, first locate the inlet pressure of 100 psig on

the vertical axis and then follow it across until reaching the curved line for 50 psi

pressure drop across the valve. Then read down to approximately 4000 for the Graph

Factor (Fg).

46

Figure 8 - Graph Factor Fg

Fsg is found using the graph in Figure 9. This graph is utilized by locating the

specific gravity of any gas (compared to air) along the horizontal axis and following it up

until reaching the curved line. Where the two lines intersect, read across to get the Fsg

factor. Because the team is using air as the gas, the Fsg is equal to one.

47

Figure 9 - Fsg Chart

Ft is found using the graph in Figure 10. To utilize this graph, first determine the

operating temperature and then locate that temperature on the horizontal axis. Follow

this line up until reaching the curved line. Where the two intersect, read across to obtain

the Ft value. The team will be operating around the 100ºF mark so the Ft value is equal

to one.

48

Figure 10 - Ft Chart

Using the previous values and an estimated air flow rate of about 3000 SCFH:

Using the table in Figure 7, the proper orifice size for the valve is ¼”. This a

rough estimate due to the fact that the airflow rate is difficult to determine due to the

transient nature of the system.

49

7 Specifications

7.1 System Specifications

The overall performance specifications for the overall system were defined for the concept development and feasibility phase. They are as follows:

The system as a whole cannot draw more than 1 amp The system has to conform to the Formula SAE rules Every component must be able to work in the approximate temperature range of 20º to 120º F

Total Budget of $500 for everything Must be weather proof (snow, rain)

7.2 Specifications for the Paddle System

20 pounds of force at a 1.6 inch shift shaft lever arm 5/8 inch bore of cylinder 380 mamps solenoid current draw Must rotate shifter shaft by 20º

7.3 Specifications for the Pneumatic System

4500 psi tank pressure 44 cubic inch tank volume 100 psi gas regulator pressure Must produce at the minimum 750 shifts per tank, preferably 2500 shifts

Must produce a shift force of 20lb The gas used must be nonflammable The tank must be of proprietary manufacture, designed and built for the pressure being used, certified by an accredited testing agency in the country of its origin and labeled/stamped appropriately

Pressure regulator must be mounted directly to the gas tank Gas tank must be securely mounted to the frame, engine, or transmission

Axis of the gas cylinder must not point at the driver Must be insulated from any heat sources (exhaust) Lines and fittings must be appropriate for the max operating pressure of the system

50

Lines must be protected from damage resulting form the failure of rotating equipment

51

8 Preliminary Design

8.1 Design Elements

Paddle/Push Button Shifting Flat Shifting Automatic Up-Shifting Two Stage Rev Limiter Gear Indicator Correct Shift Detection

8.2 Materials

Paddles and buttons for steering wheel System Controller Autronic ECU Pneumatic System

- Air Tank- Regulator- Control Valve (Grainger Alpha Series A712SD-012-D)- Cylinder- Hoses, fittings, mounting brackets

Electronics- Relays (5)- Resistors (9)- LEDs (6)- Buttons- Switches- Solenoid

52

8.3 System Operation

Figure 11 - Complete System Schematic

53

8.3.1 Paddle/Button Shifting

There will be two rear-mounted paddles and two spoke-mounted buttons mounted to

the steering wheel. One set (right) will be for up-shifting the car the other (left) for

down-shifting. When a button is pressed, the controller signals the pneumatic system and

the gear is changed. This is accomplished by the following procedure (see figure 11):

Driver activates a paddle or button The controller receives a signal that a shift is requested The controller checks if the shift is valid, for example the car is not in top gear

when an up-shift is requested, or in neutral when a down-shift is requested The controller then signals the proper relay depending on if an up or down shift

was requested The output from the relay is switched from ground to +12V The control valve is connected to the relay output and when it receives +12V it

allows air to flow into the proper side of the cylinder The cylinder is pressurized and moves its arm, which is connected to the

transmission A sensor mounted on the transmission tells the controller the position of the

transmission If the gear change fails, the controller repeats the signal to shift This repeats until the gear is changed or a set number of attempts have failed

54

8.4 Flow Charts

Flow charts were created to view the process for the flat shift (figure 12) and the

automatic up-shift sequence (figure 13).

Figure 12 – System Flowchart

55

Figure 13 – Auto Up-shift Flowchart

56

Figure 14 - Pneumatic System and Controls

8.5 Flat Shifting

Flat shifting temporarily retards the engine to prevent damage to the transmission

when up-shifting at full throttle. This eliminates the need for the driver to lift his foot off

the accelerator, saving time. It does this by interrupting the flow of fuel from the fuel

injectors and retarding the spark produced by the spark plugs. A relay is placed between

the fuel controller and the fuel injector which interrupts the signal going to the fuel

injector when activated. A second relay is placed between the coils that produce the

spark and ground, when activated the relay breaks the ground connection of the coils.

57

When an up-shift signal is received by the controller it will activate the relays

mentioned above. This will temporarily prevent the engine from operating, no matter

what the position of the throttle. Once the shift is complete the controller will allow the

relays to move back to their rest positions and normal engine function will resume. (see

figure 15).

Figure 15 - Flat Shift System

8.5.1 Automatic Up-Shifting

The automatic up-shifting system will have an on/off switch to control its

operation. If the system is active, it will send an up-shift signal to the controller when a

predetermined revolutions per minute (RPM) is achieved. This will allow the car to shift

at an exact RPM and increase performance in acceleration competition.

An RPM sensor is currently installed in the car. It produces a 12V square wave

with a frequency that varies in proportion to the RPM of the engine. The controller has

58

the capability of measuring the frequency of a signal. This will allow the controller to

activate an up-shift at a precise RPM. The controller can only handle signals less than or

equal to 5V, therefore before the signal is sent to the controller, it is passed through a

voltage regulator which will reduce the signal from a 12V square wave to a 5V square

wave.

As can be seen in figure 16, the RPM sensor’s output is being fed through a set of

resistors to step down the waveform then being fed into the controller which activates an

up-shift when the proper frequency is reached.

Figure 16 - Automatic Up-Shift

8.5.2 Two Stage RPM Limiter

The purpose of the two stage rev-limiter system is to improve the acceleration of

the car when starting from a complete stop. The system works by only allowing the

engine to reach a set predetermined RPM while engaged. This will allow the driver to

hold the throttle fully open, then release the clutch and begin accelerating without

spinning the wheels or bogging the engine. The system is controlled by a switch that

59

when closed will limit the RPM the engine produces and when released will allow for

normal engine operation. Figure 17 illustrates the operation of this system. The coolant

temperature sensor input on the electronic control unit (ECU) and the coolant temperature

sensor are separated by a relay. This relay is activated by closing the switch and allowing

12V to reach the input of the relay. As a result the ECU sees the coolant temperature as

127˚C. A preprogrammed table inside the ECU called the rev limit table can be changed

to allow different maximum RPM based on the coolant temperature. This table will be

adjusted to allow the optimal RPM when the coolant temperature is in excess of 120˚C.

Figure 17 - Two Stage Rev Limiter

8.5.3 Current Gear Display

This system shall display the current gear to the driver of the car via a row of light

emitting diodes (LED). The display will be mounted on the dashboard of the car to allow

the driver to view it with greater ease.

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The display will be updated by the controller. When the car is started, a sensor

mounted on the transmission (see Correct Shift Detection for more information on the

operation of this sensor) will indicate to the controller the current gear of the car. The

controller then illuminates the corresponding LEDs. As the transmission is moved

through the gears the transmission sensor will continuously update the controller on the

current gear being used.

Figure 18 - LED Gear Display

8.5.4 Correct Shift Detection

The transmission being used on this car does not have synchronizers, and

therefore can on occasion not change gears when needed. To handle this problem, the

system will check that the proper gear was reached and attempt to correct the problem if

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possible. A rotational position sensor will be mounted onto the transmission and provide

the controller with data indicating the current gear being used. When a shift signal is

received by the controller, whether from the driver or automatic up-shift system, the

controller will activate a shift. The current gear sensor will then be looked at by the

controller to ensure the shift took place. If the shift was not successful the controller will

send another shift signal to the pneumatic system. This will continue until the proper

gear is reached or it has failed a given number of times. This system will also be used to

prevent a shift from occurring when it is not possible. For example, if the driver signals

for an up-shift when the car is in the top gear or a down shift when in neutral (lowest

gear).

8.5.5 Pneumatic System

This system provides the power to move the transmission into another gear. It is

controlled by the electrical system previously described. The system, as seen in figure

19, is power by an air tank that holds a supply of compressed air. The tank is connected

to a regulator which limits the amount of pressure the rest of the system will see to

100psi. A control valve is placed inline after the regulator which controls the air flow to

the cylinder. The control valve is controlled by electrical signals that allow it to let air

into either side of the cylinder or prevent air from flowing to the cylinder while letting the

air in the cylinder escape. When pressure is allowed into the cylinder from the control

valve it acts on an arm which can be either moved in or out. This arm then acts on the

transmission changing the current gear.

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Figure 19 - Pneumatic System

8.5.6 Microprocessor Code and Pertinent Information

Appendix B contains the prototype code for the microprocessor to be used in the

Formula SAE car’s Driver Aids Package. The processor being used is a Basic Stamp II,

manufactured by Parallax (www.parallax.com). It has 16 I/O pins and utilizes a form of

basic for its primary control. Each I/O pin is controlled by the digital signal processor

where a threshold voltage of 2.5 volts delineates between a high state of 1 and a low state

of 0. The stamp utilizes EEPROM to store the last program uploaded via USB. This

program will automatically be started every time the stamp is powered up. While

running, the program can be reset to it’s initial state by depressing the momentary reset

button.

The code will enable easy manipulation of user/driver defined variables, such as

shift points as well as max retries when a missed shift is detected. This can be found

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under the ‘User Defined Constrains’ heading. Further modifications can be made in the

following lines of code.

Debugging can be made easier by running the code while connected to a

computer. All statements initialized with a ‘Debug’ command will be displayed on a

terminal window of the attached computer.

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9 Future Plans

The future plans for this team and the project will be focused and diligent. They

will include ordering all the necessary parts, writing the code needed for the processor,

building and assembling the system. Adequate time will then be needed to test and adjust

the system. There will be a complete working system by the end of May.

9.1 Focus

The focus will be to make the system work correctly. The exact placement of

components such as the air tank is not critical to this project because when/if the system

is to be integrated onto a competing car that has not been built. This means, among other

things, that the center of gravity will be different and the frame parameters will differ.

Therefore, making a reliable, working system will be more beneficial to the RIT Formula

team.

9.2 Paddle Shifting

The paddle shifters along with the pneumatic pieces will consume a majority of

our time. This will include steering wheel mounted shifting paddles on the back of the

wheel along with front wheel mounted shift buttons. The paddles will be made and the

buttons and switches for the paddles will be purchased. The mounting brackets will need

to be made and fitted. The electrical wires will have to be run throughout the car,

although the placement of these wires isn’t critical because they will be run differently in

the competition car. The controller with the processor will need to be mounted in a safe

central position that is again not a critical placement. The bracket for the cylinder and the

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actuator will need to be made. All the air lines will need to be run and once everything is

mounted, the system will need to be tested and tuned.

9.3 Flat Shift

The flat shift system will be built independent of the Autronic engine

management system that is currently being used. The element of this system that will

take the longest is figuring out the delay times. These are quite critical because every

millisecond counts. There will need to be testing done to make sure the fuel and spark

are cut for the correct amount of time. Too much will slow acceleration times, not enough

could damage the transmission. Once the code is written and proved to work, the

changing of the retarding times will be easy, however the actual testing will be time

consuming because it will involve driving the car, which will most likely be done by

members of the formula team.

9.4 Automatic Up-shift

The automatic up-shift system should be relatively straightforward compared to

other parts of this project. Mounting and wiring of a switch for the system will be done.

Using the Autronic system, the system should be easily changeable and tunable. The full

use of this system will come when it uses the flat shifting system, after it is complete.

9.5 Launch Procedure

The launch system will be comparatively simple to make, but may be more time

consuming to test. A switch will be mounted and wired to turn the system either on or

off. The appropriate RPM value to start the car at will need to be determined. Then the

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car will be tested and the RPM value will be changed. Again, the testing will probably be

done by the members of the Formula team, who will have limited time to do this.

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Appendix A - Abbreviations

Acnp = Area of the cylinder non-plunger side [m2]Acp = Area of the cylinder plunger side [m2]Aps = Area of the plunger shaft [m2]Cp = Specific heat at constant pressure [(N*m)/(kg*K)]Cv = Specific heat at constant volume [(N*m)/(kg*K)]Dcb = Cylinder bore diameter [m]Dl = Line diameter [m]Dps = Plunger shaft diameter [m]Fg = Force with given pressure (for given cylinder) [N]Fs = Force required to shift [N]Lcs = Cylinder stroke [m]Ll = Line Length [m]Ma = Useable mass of gas [kg]Mc1a = Mass of gas in cylinder and line at position 1 at pressure of atmosphere [kg]Mc1r = Mass of gas in cylinder and line at position 1 at pressure of regulator [kg]Mcl2 = Mass of gas used per shift (Mass in cyl and line at pos 2 and Rrabs – Mass in cyl and

line at pos 1 and patm) [kg]Mf tank = Mass of gas in full tank [kg]Mt = Mass of air in full tank [kg]Mt min = Mass of air in tank at minimum regulator pressure [kg]Ns = Total Number of ShiftsPatm = Pressure of the atmosphere [Pa]Pr = Gage pressure of the regulator [Pa]Pr min = Minimum regulator gage pressure (for given cylinder to shift) [Pa]Prabs = Absolute pressure of the regulator [Pa]Pt = Gage pressure of the tank (max) [Pa]Ptabs = Absolute pressure of the tank (max) [Pa]R = gas constant [(N*m)/(kg*K)]Ta = Tank air temperature [ºC]Ta1 = Temperature of air at position 1 at regulator pressure [K]Ta2 = Temperature of air at position 2 at regulator pressure [K]Tabs = Tank air temperature absolute [K]Vc1 = Cylinder volume at position 1 [m3]Vcl1 = Cylinder and line volume at position 1 [m3]Vc2 = Cylinder volume at position 2 [m3]Vcl2 = Cylinder and line volume at position 2 [m3]Vcr = Volume of retracted cylinder [m3]Vl = Line VolumeVtank = Volume of the tank [m3]

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Appendix B – Microprocessor Code

' $STAMP BS2

'-------------------------------------------'-------------------------------------------' Formula SAE Senior Design' Inital Creation Date: 2/14/05' Current Version .1' Doug Payne'' Pin Designations' Pin 0 = Upshift' Pin 1 = Downshift' Pin 2 = Auto Upshift Enable' Pin 3 = Gear Selection Indication' Pin 4 = first gear led' Pin 5 = second gear led' Pin 6 = third gear led' Pin 7 = forth gear led' Pin 8 = fifth gear led' Pin 9 = neutral led' Pin 10 = Auto Upshift led' Pin 11 = Trans Drum Encoder' Pin 12 =' Pin 13 =' Pin 14 =' Pin 15 ='-------------------------------------------'-------------------------------------------

'-------------------------------------------'-------------------------------------------' Variable Declarationsrpm VAR Wordshiftpoint VAR wordshift_pause_duration VAR wordgear VAR bytegear_encoder VAR Wordi VAR wordrepeat_try_missed VAR byterepeat_try_missed_max VAR byte'-------------------------------------------'-------------------------------------------

'-------------------------------------------'-------------------------------------------' User Defined Constraintsshiftpoint=10000 'Auto Upshift shift 'point in RPM

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shift_pause_duration=30 'pause in msrepeat_try_missed_max=5 'max number of 'missed gear attempts'-------------------------------------------'-------------------------------------------

'-------------------------------------------'-------------------------------------------' Start Up Sequence'-------------------------------------------'-------------------------------------------HIGH 15HIGH 6PAUSE 75HIGH 14HIGH 7PAUSE 75HIGH 13HIGH 8PAUSE 75HIGH 12HIGH 9PAUSE 75HIGH 11HIGH 10PAUSE 200LOW 15LOW 14LOW 13LOW 12LOW 11LOW 10LOW 9LOW 8LOW 7LOW 6LOW 5LOW 4LOW 3LOW 2LOW 1LOW 0'-------------------------------------------' Main Program'-------------------------------------------shiftpoint=shiftpoint/600 '100ms unitsmain:LOW 10 'Auto Upshift led offrepeat_try_missed=0

IF IN0=1 THEN upshift 'Pin 0 UpshiftIF IN1=1 THEN downshift 'Pin 1 DownshiftIF IN2=1 THEN autoupshift 'Pin 2 Auto Upshift EnableGOSUB current_gear

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GOTO main

'-------------------------------------------' Automatic Upshift'-------------------------------------------auto_upshift_start:HIGH 10 'Auto Upshift led onIF IN2=0 THEN main

COUNT 4,100,rpm 'Pin 4, 100ms, rpm outputIF rpm>shiftpoint THEN upshiftGOTO auto_upshift_start:

'-------------------------------------------' Upshift'-------------------------------------------upshift:IF gear=5 THEN maingear=gear+1upshiftloop:HIGH 5 'cut fuelHIGH 6 'cut sparkHIGH 7 'upshiftPAUSE 35 '35 ms pause for upshiftLOW 7LOW 5LOW 6

repeat_try_missed=repeat_try_missed+1 'repeat max times

IF repeat_try_missed=repeat_try_missed_max THEN error

GOSUB current_gearIF currentgear<gear THEN GOTO upshiftloop

RETURN

'-------------------------------------------' Downshift'-------------------------------------------

downshift:IF gear=0 THEN maingear=gear-1downshiftloop:HIGH 5 'cut fuelHIGH 6 'cut sparkHIGH 8 'upshiftGOSUB shiftpauseLOW 7LOW 5LOW 6

repeat_try_missed=repeat_try_missed+1 'repeat max times

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IF repeat_try_missed=repeat_try_missed_max THEN error

GOSUB current_gearIF currentgear>gear THEN GOTO downshiftloop

GOTO main

'-------------------------------------------' Shift Pause'-------------------------------------------shiftpause:FOR i=0 TO shift_pause_durationPAUSE 1nextreturn

'-------------------------------------------' Neutral'-------------------------------------------neutral:gear=0HIGH 9LOW 4GOTO main

'-------------------------------------------' First Gear'-------------------------------------------first:gear=1HIGH 4LOW 5GOTO main

'-------------------------------------------' Second Gear'-------------------------------------------second:gear=2HIGH 5LOW 6GOTO main

'-------------------------------------------' Third Gear'-------------------------------------------third:gear=3HIGH 6LOW 7GOTO main

'-------------------------------------------' Forth Gear'-------------------------------------------forth:

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gear=4HIGH 7LOW 8GOTO main

'-------------------------------------------' Fifth Gear'-------------------------------------------fifth:gear=5HIGH 8GOTO main

'-------------------------------------------' Current Gear Verification'-------------------------------------------current_gear:PULSIN 11,1,gear 'RC curcuit for pot

IF (gear_encoder > 4000) THEN DEBUG "5th Gear" currentgear=5 ELSEIF (gear_encoder > 3500) THEN DEBUG "4th Gear" currentgear=4 ELSEIF (gear_encoder > 3000) THEN DEBUG "3rd Gear" currentgear=3 ELSEIF (gear_encoder > 2500) THEN DEBUG "2nd Gear" currentgear=2 ELSEIF (gear_encoder > 2000) THEN DEBUG "1st Gear" currentgear=1 ELSE DEBUG "Neutral" currentgear=0 ENDIFreturn

'-------------------------------------------' Exceded Max Retrys'-------------------------------------------error:DEBUG CR, "shifting error: Exceded Max Retrys "GOTO main

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“Asco Valve”, 2005. Asco. Feb 9, 2005. <http://www.ascovalvenet.com/AscoValvenet/Applications/LiteratureRequest/LRPublicWeb.aspx?action=add>.

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Boylestad, Robert L. Intoductory Circuit Analysis, 9 th Ed. Upper Saddle River, NJ:Prentice-Hall, 2000.

“Display Products”, 2005. Crossfire. Feb 8, 2005.<www.crossfireinc.com/categories.asp?cat=17>.

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Fox, Robert W. and Alan T. McDonald. Introduction to Fluid Mechanics, 5 th Ed. NY:John Wiley & Sons, 1998.

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“Generation E – Browsing Nitro Tanks and Covers”, 2005. Generation E. Feb 8, 2005.<display.genenow.com/index.cfm?fuseaction=catalog.catalog&categoryID=19>.

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“McMaster-Carr”, 2005. McMaster-Carr. Feb 12, 2005. <www.mcmaster-carr.com>.

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“Paintball Adreneline – System X VENGEANCE HIGH FLOW 2PC REGULATOR –Black”, 2005. Painball Adreneline. Feb 9, 2005.<www.paintballadreneline.com/v2/customer/product.php?productid=17123&...>.

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