UNIVERSITY OF VERMONT
AERO SEED Shifter
UVM AERO
Matthew Girouard, Stephen Gross, Nicholas Peterson, Michael Rogals II
Advisor: Jeff Frolik, Ph.D.
Contact: npeterso@uvm.edu
UVM AERO SEED
TABLE OF CONTENTS
Executive summary ........................................................................................................................................ 2
Final Design concept ...................................................................................................................................... 3
overview of shifting system ........................................................................................................................ 3
system management .................................................................................................................................... 4
Microcontroller/CAN Overview ............................................................................................................. 4
Gas Engine, Electric Motor and Clutch Management ............................................................................ 5
implementation ........................................................................................................................................... 9
Layout in Car .......................................................................................................................................... 9
Driver Interface ..................................................................................................................................... 11
Justification................................................................................................................................................... 13
Choice of Project ...................................................................................................................................... 13
Transaxle .................................................................................................................................................. 14
CO2 vs Solenoid vs Manual ...................................................................................................................... 15
Arduino & Controller ............................................................................................................................... 16
CO2 Canister Protection ............................................................................................................................ 16
Work plan & budget ..................................................................................................................................... 17
Appendices ................................................................................................................................................... 19
Shifting Logic Flow Charts ...................................................................................................................... 19
Electric Only Mode .............................................................................................................................. 19
Gas Only Mode ..................................................................................................................................... 22
Pugh Chart ................................................................................................................................................ 25
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EXECUTIVE SUMMARY
The Alternative Energy Racing Organization (AERO) is a student run club of roughly 25 members at
the University of Vermont dedicated to learning, implementing and advancing hybrid technology.
Each year, a formula style car is built from the ground up by students. The car is judged on its design
as well as its performance in static and dynamic events. At the International Formula Hybrid event
in Loudon, New Hampshire this past May, AERO competed with a strong showing from their car.
The car’s success was attributed in large part to the car’s custom power train. This power train is a
parallel hybrid transaxle in which the internal combustion engine is coupled to the electric motor via
the main shaft of the transmission. This allows both systems to propel the car at the same time. The
internal combustion cylinder, clutch, and transmission are all stock parts from a 250cc Honda dirt
bike. The electric motor is an AC31 3-phase induction motor from High Performance Electric
Vehicle Systems.
However, the architecture of this custom hybrid power train led to an unforeseen problem. At the
competition this past May, the driver was sitting in the car attempting to warm up the gas engine. He
was revving the hybrid drive train with the transmission in neutral in order to warm it up as fast as
possible. Once the engine was warm, he released the accelerator and the gas engine spun down like
any normal gas engine. However, when the electric motor has no throttle input, it freewheels;
meaning that it spins freely and gradually slows down. This electric motor is nearly silent when it
freewheels and with the engine noise, the driver had no idea that it was still spinning. The rotor of
the electric motor weighs roughly 40 pounds and was spinning at approximately 4000 rpm at this
point. When he put the car in gear, the static wheels and drive shafts were immediately impacted with
the inertia from the still spinning electric motor. This powerful shock stripped the teeth from two of
our transmission gears, rendering the car inoperable.
This happened because the driver did not have enough feedback from the hybrid power train to make
an informed decision on whether or not to shift. In an effort to stop this from happening again, we
plan to implement an intelligent shifting system in the car. This system will have the ability to make
go/no-go decisions of whether or not to perform a shift based on drive train sensors and user inputs.
If the shifting system deems it okay to shift, it will manage the physical aspects of the clutch and
shifting operations.
This system will take responsibility off of the driver, decrease shift times, and make the hybrid power
train safer. The driver will no longer have to worry about transaxle specifics or take their hands off of
the steering wheel to shift. In addition, the driver will have one less pedal to manage while driving.
We believe this will make the driving experience much easier and safer. This will also enable
effective driving of the car by non-seasoned members of the club and increase driver confidence by
enabling racing without fear of breaking critical components. The shifting system will use CO2 to
actuate pistons that will control the clutch and shifter levers. These pistons will be actuated by
computer controlled CO2 valves when driver inputs are pressed. We plan to implement our system
into AERO’s 2011 competition car with the final goal of having our shifting system help the AERO
team succeed at the 2011 Formula Hybrid Competition.
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FINAL DESIGN CONCEPT
OVERVIEW OF SHIFTING SYSTEM
Figure 1: A schematic view of the AERO shifter, a computer controlled, CO2 actuated system
The shifting system will be an intelligent, automated procedure for shifting the formula hybrid
racecar. In this shifting system, the CPU takes inputs from the driver and from onboard sensors.
It then makes go/no-go decisions on whether or not to shift depending on a number of
parameters. If a “go” decision is reached, the CPU will activate the appropriate valves and CO2
will flow into the actuators, articulating the shifting and clutch levers. A schematic of the shifting
system’s architecture can be seen in Figure 1. The Engine/Motor Management section can be
seen for more details on the shifting procedure.
The driver inputs are upshift, downshift, and find neutral. The sensor inputs are electric motor
rpm, gas engine rpm, and wheel speed. The motor rpm will be collected from the motor
controller which communicates the info via a serial bus. The engine rpm will be obtained via a
capacitive sensor on the spark plug line. This is monitored by a microcontroller that will
communicate the data via CAN. Wheel speed will be obtained by a magnetic sensor on the
wheels which will also be monitored by a microcontroller and communicated to the shifter CPU
via CAN. The CO2 system components shown below in Figure 2 consist of a CO2 tank, remote
pressure gauge, two valves, one bidirectional actuator, one unidirectional actuator, and various
lengths of pressure hose.
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Figure 2: Components of off shelf Bi-Performance CO2 shifting system
The decision made by the microcontroller is based on the reported wheel-speed and motor rpm.
For example, if an upshift from neutral is requested by the driver, the CPU will first check last
reported wheel speed and motor rpm. Ideally the wheel speed and motor rpm should be zero
when shifting from neutral to first gear. Then, the CPU will compare the wheel speed/motor rpm
against the accepted ratio necessary to allow a shift up from neutral. If the value for the
algorithm is not acceptable, then the CPU will disallow the shift. In the case of any other upshift,
the wheel speed function is overlooked. When downshifting, wheel speed will be monitored to
facilitate rev matching.
SYSTEM MANAGEMENT
Microcontroller/CAN Overview
Figure 3: Arduino Uno Microcontroller
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The microcontrollers used in our shifting system are ATMEL Atmega 328s implemented in an
Arduino Uno breakout board. This is an open-source development tool that is used extensively
by hobbyists. The inter-microcontroller communication system used in the AERO car is
CAN2.0B and will be used with our shifting system as well. CAN stands for Controller Area
Network and is a standard used in the automotive industry.
Gas Engine, Electric Motor and Clutch Management
The clutch, electric motor, gasoline engine, and transmission need CPU management in order for
the system to shift without human control. The shifting system uses two CO2 actuators to
accomplish this task. A unidirectional actuator will physically disengage the clutch. A second,
bidirectional actuator will physically manipulate the shifting lever up and down. In addition, the
CPU will have final control over throttle inputs to the gas engine and electric motor.
The parallel architecture of the hybrid transaxle allows the car to have three drive modes; gas
only, electric only, and full hybrid. In each of these modes the shifter must have downshift, up
shift, and find neutral capabilities. This means that we need nine completely unique procedures
for the shifter to follow depending on the drive mode and the driver input.
The following is an explanation of the process for the hybrid find neutral, up shift, and down
shift. The explanations are referring to Figures 4-6. For the gas only and electric only drive mode
flow charts, refer to Figures 17-22 in the Appendices. It is important to note that the transmission
is sequential in order to fully understand the following flowcharts.
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Figure 4: Hybrid Down Shift
For full hybrid downshift, the CPU first checks to see if the “downshift” user input has been
pressed. At this point if the button was not pressed, nothing will happen and the CPU will move
on to other tasks. However, if the button was pressed then the CPU will check the gear position
sensor to determine its next course of action. If the car is in neutral, it will not downshift and the
CPU will again move on to other tasks. If the car is not in neutral the CPU will check last
recorded engine rpm to see if it is possible to downshift without over-revving the gas engine. If
engine rpm is low enough, it will go ahead with the physical shifting sequence, if not, the CPU
will move on. In order to physically shift, the first thing the CPU will do is actuate the clutch,
and then it will make the motor freewheel. Next it will physically actuate the shifter down, rev-
match the internal combustion engine to match wheel speed, re-engage the motor, and finally
release the clutch. This will complete a single down shift.
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Figure 5: Hybrid Find Neutral
The hybrid find neutral flow chart will begin the same way as the hybrid downshift flowchart. It
will check to see if the find neutral button is pressed. If it is not, then nothing will happen and the
CPU will move on. If the button is pressed then the CPU will check the gear position sensor to
see if the transmission is in neutral. If it is, then the CPU will move on. If the car is not in
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neutral then it will check if it is in 1st gear. If it is not in first, then it will disengage the clutch,
freewheel the motor, and actuate the shifter down repeatedly until the car is in 1st gear. Once the
car is in first gear the CPU will again disengage the clutch and freewheel the motor. Then the
CPU will actuate a half-duration downshift to engage neutral, re-engage the motor, and release
the clutch. This will complete a full hybrid find neutral command.
Figure 6: Hybrid Upshift
The hybrid upshift flow chart will begin the same way as the previous two. It will first check if
the up shift button has been pressed. If it has, the CPU will check if the car is in neutral. If the
car it is in neutral, it will see if the wheel speed matches the motor rpm through the use of the
associated sensors. If the wheel speed and motor rpm do not match, then the CPU will cancel the
shift and move on to other tasks. If the wheel speed and motor rpm match, then it will check the
gear position sensor to see if the car is in 5th gear. If it is in 5th gear it cannot up shift anymore, so
the CPU will cancel the shift and move on. If the car is not in neutral or 5th gear, the CPU will
go ahead with the physical shift and ground the spark plug, freewheel the motor, actuate the
shifter up, re-engage the motor, and un-ground the spark plug. This completes one up shift
process.
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IMPLEMENTATON
Layout in Car
Figure 7: Layout of CO2 canister
In the figure above the location of clutch lever and shifter locations are shown in the car. We will
need to run high pressure lines from the CO2 canister to actuate the shifter and clutch. In
addition, the preliminary CO2 canister location is also shown. A protective casing for the canister
will be manufactured from 6061 aluminum. The CO2 pressure gauge will be displayed on the
dash. Below, Figure 8 shows a magnified region to better show the clutch and shifting drum.
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Clutch
Shifting Drum
Figure 8: location of the clutch lever and shifting drum
We will mount the actuators from the Biperformance system to the clutch lever and the shifting
drum lever shown above. We will make tabs that will hold the actuators to the frame of the car.
The shifting lever needs to move in 2 linear directions, one to upshift and the other to down shift.
When the valve opens the actuator will fill with pressurized CO2 and move the actuator in the
direction that is necessary.
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Driver Interface
Figure 9: Driver Interface
Figure 1-a above shows the schematic of the cockpit as seen by the driver. The highlighted
balloons indicate the components of our project incorporated to the dash of AERO’s 2011
competition car. The club already has a designated group to design and fabricate the dash/driver
interface. Therefore, the scope of our project does not include the completion of the dash.
However, the driver inputs (i.e shift paddles, find neutral and C02 read out gage) are part of our
project. These components are required to successfully implement our shifting system into the
car.
The driver inputs incorporate the human element into our project. Below is a summary of the
driver inputs required to operate our system.
Components and their Functions:
1. C02 Pressure Gauge: driver is required to monitor this gauge.
Also, when the gauge approaches empty the driver should
replace the C02 reservoir. Bi-performance estimates ~1000
shifts per canister. The gage implemented into the car will
look similar to figure 1-b.
Figure 10: Pressure Gauge
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2. Up-shift: paddle is depressed by driver. Clutch, motor
speed, engine speed, throttle and shift are taken care of by
our system. While the up-shift routine is being executed
the driver is expected to maintain control of the car. At
the completion of the routine the transmission will have
advanced one gear position, clutch is re-engaged and the
driver’s throttle input controls the speed the of car. The
shifting paddles implemented in the car will look similar
to figure 1-c.
3. Downshift: paddle is depressed by driver. Clutch, motor
speed, engine speed, throttle and shift are taken care of by Figure 1-c
our system. While the down-shift routine is being
executed, the driver is expected to maintain control of the
car. At the completion of the routine the transmission will
have moved down one gear position, clutch is re-engaged
and the driver’s throttle input controls the speed of car.
The shifting paddles used in the car will look similar to
figure 1-c above.
4. Find Neutral: button is depressed by driver. Clutch, motor
speed, engine speed, throttle and shift are taking care of by
our system. While the find neutral routine is being
executed the driver has no expected inputs. At the
completion of the routine, the transmission will be in the
neutral position. The button implemented in the car will
Figure 11: Driver Input
look similar to figure 1-d. Button
Figure 1-d
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JUSTIFICATION
Choice of Project
The transaxle in the AERO car is a homemade design that puts the center differential, rear
differential, transmission, motor, clutch, and engine all in one case. UVM is the only team at the
race that has a power system that is this fully integrated. Using a fully integrated system makes
the car fairly similar to a system that would be implemented into an everyday car, such as those
made by Toyota, GM or Ford. This system is beneficial because it replaced the chain drive
system from previous iterations with a gear drive system. It requires only one reservoir of oil,
and lowered the center of gravity in the car by about 6 inches. When driving in electric only
mode, one can hold the engine clutch and drive easily with only the electric motor. The downside
to this set up is that the electric motor spins whenever the main transmission shaft spins. This
means that if we want to drive gas only, the electric motor acts as a giant flywheel. In this set up
if the electric motor is spinning, and is inadvertently coupled to transmission gears which are
spinning at a different rate, disaster results. Unfortunately, as was mentioned previously, UVM
AERO experienced this at last year’s Formula Hybrid Competition. The transaxle has beneficial
characteristics, but it comes with the need for protective measures and overrides.
Keeping the transaxle safe is the main justification for our senior design project, while other
reasons include making driving easier, taking responsibility off of the driver, and creating
fast/efficient shifts. We want to protect the transaxle because of its importance for a functional
car, as well as ensuring that the transaxle does not break due to its high replacement cost.
Protecting gears in the transmission from excessive torque is our key goal.
To maintain control of the transaxle we will implement a CPU controlled CO2 shifting system. In
short, the shifting system will ground the spark plugs during upshifts or actuate the clutch lever
during downshifts, while simultaneously moving the shifting drum. Critical data from the motor,
engine, and wheels will be monitored by the CPU to ensure that the driver won’t shift at
inopportune times. In addition, for a fast and efficient race car, minimizing shift times and rev
matching are necessary to decrease time spent between gears. Whenever a racecar is between
gears, it is not accelerating, essentially losing time. The repeatability and speed of the CPU plays
a crucial role in making sure all these functions are carried out smoothly. The desire for full
throttle upshifting is the driving force behind the decision to ground the spark plug on upshifts
and only use the clutch when downshifting. A full throttle upshift occurs when pressure is not
removed from the gas pedal during the shift. If the clutch were used on the upshift, then the gas
pedal would need to be released to keep the engine from over-revving. By grounding the spark
plug during an upshift, the engine is briefly killed freeing the transmission gears and allowing the
driver to apply constant pressure to the gas pedal during the shift.
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Transaxle
The external components of the transaxle are shown below in Figure 4. This helps show how the
electric motor and gas engine are positioned, and paired together with the rear differential.
Figure 4: External Components of Transaxle
Below, in Figure 5, the housing of the transaxle has been removed to display the internals and show how
the electric motor and gas engine are coupled together.
Figure 12: Internal Components of Transaxle
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CO2 vs. Solenoid vs. Manual
In previous years, AERO has used a manual shifting system on the car. In an effort to upgrade
this year’s car, protect transaxle components, and make more efficient shifts, solenoid and CO2
shifting systems were compared to find the best solution. We first compared power curves of a
manual shifter and an automated shifter to justify that a solenoid or CO2 shifter is in fact more
efficient at shifting. Below is a power vs. time overlay comparing a manual shifting motorcycle
and a Biperformance CO2 shifter. It is quite plainly seen that the Biperformance shifter provides
quicker shifts and higher power output.
Figure 13: Power vs. time curve overlay of a manual shifter (red) and a Biperformance CO2
shifter (blue) (Source: Biperformance)
When considering the two types of shifters, CO2 and solenoid, the first thing realized was that the
solenoid shifter weighed considerably more. Not only was one solenoid heavier than the CO2
canister and components, but two solenoids would be needed for our application; one for the
shifter and one for the clutch. The CO2 system uses only one CO2 bottle that feeds both the
shifter and the clutch levers, which results in a system that weighs considerably less. When
building a racecar, weight saved in the car results in quicker times on the race track. Another
factor considered was the energy consumption of each system. A solenoid shifter requires that
large amounts of energy be used to two throw two plungers with enough force to depress the
clutch and shifter levers. This will not only require around 50 amps at 12 volts to actuate, but
will heavily tax the battery system. This will make the car less efficient and result in a battery
that is drained quickly. The CO2 systems only electrical requirement is for two small valves to be
actuated; drawing approximately 2 amps at 12 volts. In the end we decided to use a CO2 system
that is a modified off-the-shelf system in order to shorten prototyping time and decrease initial
cost. A Pugh chart used to solidify our decision can be found in the Appendices.
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Arduino and Controller
The biggest driving force behind our decision to use the Arduino is the end user. AERO uses
Arduinos extensively in their hybrid racecar. As such, it makes sense to keep everything as
consistent as possible in the car. That way, in the event that changes are made to the car, future
club members should be familiar with the programming environment and modifications to the
shifter will be relatively easy. Arduinos are extremely easy for beginners to learn to program, so
a very inexperienced person can learn to modify the code in the shifter with as little effort as
possible. In addition, since the board is open source, there is a large amount of free software
available for most applications. This free software includes a number of code libraries as well as
built-in functions that are very useful.
Through the use of the CAN system chosen for our final design there is potential for to spread
out the responsibilities of the shifter CPU among several microcontrollers. This will allow us to
save weight by delegating shifting duties between existing microcontrollers instead of adding
another one to the system.
CO2 Canister Protection
The CO2 canister is a crucial and potentially dangerous part of our shifting system and therefore
must be protected from puncture, dents, excessive vibration, and other unforeseen damage. The
CO2 canister protective casing unit will be implemented in the car to prevent those events from
taking place. The CO2 canister is pressurized at 900-1000 PSI and a puncture in the CO2 bottle
would not only make our shifting system inoperative but could prove to be dangerous for the
driver and those near the car. Fabricating a casing unit for the canister will also provide an easy
way of mounting the CO2 bottle to the frame and will make replacing the bottle much faster and
simpler.
The external structure and the mounting brackets will be fabricated from 6061 aluminum, as it is
lightweight, strong, and easily machined. The inside of the protective casing will be lined with a
¼ inch of open cell, sponge rubber which will absorb impact and create a snug fit for the CO2
bottle. The top will contain a hole for the exiting CO2 line and will use three set screws to affix it
to the aluminum protective casing.
Figure 14 Protective casing and CO2 canister exploded view
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WORK PLAN AND BUDGET
When we return from winter break, there will be a steady work load all semester leading
up to Design Night on May 4th. All Biperformance components should be in house come
January, and solid modeling of all the pieces will begin immediately. These modeled
components will allow us to add them to the AERO car assembly and finalize their
locations. In addition, this will help us determine lengths of hosing, required mounting
hardware, etc. Work will then start on adding the new shifting system to our transaxle test
bench. The next step will be wiring, routing pneumatic hosing, and create a tuning device
for altering engine kill timing and shifter-clutch actuation timing. The shifter-clutch
actuation timing is the time between disengaging the clutch, actuating the shifter, and then
reengaging the clutch. This is necessary to find out how quickly a shift can be performed
safely. After everything is running smoothly on the test bench, the system will then be
moved to the car where additional testing will take place. A detailed Gantt Chart is below.
Figure 15: Spring Semester 2011 Gantt Chart
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Below is the projected budget for our project.
BUDGET
Component Vendor Specifications Cost
FX- Shifting System Bi-Performance Kart Shifter $965.60
Aluminium Tubing Speedy Metals 12" of 2.875" OD 2.468" ID $13.47
Aluminium Round Stock Speedy Metals 3.25" OD 5" Long $22.85
Brackets for Canister Triangle 2 Brackets $100.00
Shifter Paddles TBD $500.00
Clutch Pedal TBD $100
Clutch Pedal Brackets TBD $100
Morse Cable TBD $10
$1,851.92
Figure 16: Budget plan
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Appendices
Electric Only
Downshift:
Figure 17: Flow Chart for Electric only Downshift
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Find Neutral:
Figure 18: Flow Chart for Electric only Find Neutral
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Upshift:
Figure 19: Flow Chart for Electric only Upshift
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Gas Only
Downshift:
Figure 20: Flow Chart for Gas only Upshift
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Find Neutral:
Figure 21: Flow Chart for Gas only Find Neutral
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Upshift:
Figure 22: Flow Chart for Gas only Upshift
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Figure 23: Pugh Chart
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