Engine Controls / Final Drive
Engine and Controls
Final Drive Selection
Formula SAE is annual competition that takes place every year. Competing
schools and universities throughout the world enter mini formula cars into the
competition. The event is a comprehensive design competition that judges the cars on
ingenuity, presentation, manufacturing and performance characteristics. Each entry must
comply with all FSAE rules and regulations. These rules can be found on the Formula
SAE’s official web site. The competition gives students a year to design, fabricate and
tune their formula style car. The end result is a project that challenges students to use
their engineering skills is a realistic and practical way. This senor project is based on
these regulations, so many of the geometric design dimensions are constrained to comply
with these rules. The ultimate goal for this project is produces a car that can compete and
win in this formula SAE competition.
This report focuses on the design, fabrication and assembly of the power train, and
specific design challenges that had to be solved to produce a reliable product.
Engine and Controls
Many of the parts used in this project are recycled from previous years. The cost
to replace some of these parts would be too great for each team to gather from sponsors
every year. One such part is the MoteC, which is an engine management computer. It
receives electrical signals from various sensors and in turn controls the engine’s fuel
mixture and ignition timing.
One configuration mode in which the MoteC operates is the sequential fuel
injection mode. Sequential fuel injection works by allowing the fuel injector’s pulse to
coincide with engine valve timing. As the intake valve opens to draw in a cycle of air, a
fuel injector sprays an atomized shot of fuel directly into the engine’s combustion
chamber. This cycle repeats every 2 revolutions in a four-stroke engine for each cylinder.
To maintain proper stoichiometry the CPU meters each injector’s pulse width. The CPU,
or MoteC in the case of FSAE, is constantly adjusting these pulse widths, as different
demands are required of the engine. An array of engine sensors allows the computer to
know how the engine is performing at every fraction of a millisecond. These sensors
include engine coolant temperature, intake air temperature, manifold absolute pressure,
throttle positioning, oxygen, crank shaft angle, and cam shaft angle sensors to name a
Two engine sensors are critical to sequential fuel injection operation, the cam and
crank angle sensors. The cam (SYNC) sensor tells the computer the exact position of the
camshaft. The camshaft opens and closes the exhaust and intakes valve. The Honda
motor has two over-head camshafts. One is designated for the intake valve, while the
other controls the exhaust valves. The crankshaft (REF) sensor tells the computer what
angle the crank is making, which corresponds the position of the engine’s pistons. If the
computer does not receive constant signals from these sensors, the engine cannot function
The 600cc Honda F2 CBR engine has been the workhorse of University of Utah’s
Formula SAE cars for the last several years. The high performance sport-bike engine
produces 100HP @ 12,000 and 47ft-lbs of torque @ 10,500rpm. Compared to other
engines of the same size and year, our motor produces virtually the same power and
torque outputs. The new 2005 engines are capable of marginally higher outputs of about
10 to 20 HP, however they have electronically control fuel injection systems. Despite the
power increases of the newer motor. The team decided to continue using the same engine
form previous years. The reasons for this are simple. There are three Honda F-2 engines
available for this project, which require no additional funding. To obtain a newer engine
we would have to purchase an entire bike, that would costs thousands. Secondly, The
power increases are marginal. We should be able to make up for this power differential
by converting the stock carbureted fuel system to fuel injection. If we could choose any
motor we wanted, we obviously would choose the Yamaha YZF-R6 motor that produces
123 HP stock. Interestingly, this is the motor Cornell University, last year’s FSAE
winner, used for their car. If we only had their funding.
Figure 1. Cornell University’s turbo setup.
Note the Yamaha engine behind it.
Picture courtesy of Josh Smith
Table A. The engine specification used to select the engine
Engine Stroke Power Compressio
Year Make Model Size (cc) (mmxmm) HP Torque (ft-lbs) n Ratio
1994 Honda CBR F2 600 65x45.2 100@12000rpm 47@10500 12:01
1993 Suzuki RF-600R 600 65x45.2 100@11500rpm 47.4@9500rpm NA
1994 Yamaha FZR 600 62x49.6 96@11500rpm 65.7@9500rpm 12:01
1994 Kawasaki ZZR 600 64x46.6 100@11500rpm 47.2@9500rpm NA
2005 Honda CBR F4 600 67x42.5 110@12500rpm 47.9@10500rpm 12:01
2005 Yamaha YZF-R6 600 65.5x44.5 123@13000rpm 50.5@12000rpm 12.4:01
The goal of the team is to optimize the MoteC’s operation. To do this the team
must configure the MoteC to run in a sequential fuel injection mode, which is the most
efficient mode. In past years the team has faced problems the SYNC and REF signals
and the computer would report an error. Because these signals are crucial to optimizing
the operation of the engine, a reliable system must be implemented.
The design team’s decision to use a rear sub-frame, which transfers the rear
external forces through the engine to the front monocoque body, makes the engine a
stressed member. All the parts that would allow for this rear sub-frame set-up had to be
located or manufactured. I was able to go through the tedious process of finding most the
parts used on formula cars from previous years to make this possible. This set-up is only
made possible by the use of “side plates”, which bolt directly to each sides of the engine.
The side plates become the backbone of the rear of the car. The engine, rear A-arms, coil
springs/ shock assembly, final drive, differential, main hoop/sub- frame assembly,
radiator and other miscellaneous components are connected to these side plates.
I created a mock-up of the engine, side plates, final drive, differential, axles, and
CV joints. To give my fellow team mates a visual reference of how the aft portion of the
car will function.
Figure 2. The side plates connect the
F-2 motor. The side plates, along with
the entire rear suspension of the car,
support the final drive.
Picture courtesy of Kathy Allman
Figure 3. The rear engine sub-
assembly complete with suspension and
final drive. Note how the side plates
along with the engine block support the
weight of the entire engine
Picture courtesy of 2003 U of U FSAE
To optimize the power produced by the 600cc Honda F2 motor the cam sensor
must operate reliably. Pervious teams have had problems with the cam sensor requiring
them to compromise on fuel injection and ignition system configurations. I discovered
that they attempted to uses sensor (MD HALL 437) to generate a SYNC signal.
According to MoteC’s own schematics this sensor is not recommended for anything other
then wheel speed. While the past teams had problems with the cam sensor, their REF
signal from the crank sensor was reliable. They employed a small hall-effect sensor (M
3025 SS13 DTM), which is recommended for cam and crank sensors. The simple
solution is to use the same sensor for camshaft. It should produce a reliable SYNC
signal. The only problem is designing a fixture that will allow us to use this sensor on the
camshaft. I have created a fixture and trigger wheel that should accomplish this task.
This design makes the sensor’s trigger wheel external rather internal were it is exposed to
engine oil. The motor oil will be filled with fine metal particles from the engine bearings
and clutch. These particles collect on the sensor’s magnetic face and interrupt the SYNC
signal. By making the trigger wheel external the cam sensor will not be exposed to this
contaminants. Also, the sensor to trigger wheel gap (.012 to .025 inches) will be adjusted
Gear Box/ Final Drive
To drive the racecar forward, a mechanism is required to interface the wheels and
the output shaft of the gearbox. The gearbox contains six forward gears that are
integrated inside a single engine/gear block. The motorcycle from which the engine
came employed a chain drive, which is the industry standard for most sport bikes. This
chain/ sprocket set constitutes the final drive of the motorcycle. Its drive ratio is
calibrated specifically for the rear wheel (17’’) of a motorcycle. It is not uncommon to
see motorcycles that use shaft or belt driven final drives. Our racecar does not have a
rear swing arm or a single rear wheel, so the gearbox has to be coupled in a different
configuration. Although FSAE cars use shaft, chain, belt, or gear driven final drives, the
gearbox must ultimately be coupled to a rear differential. The differential transfers power
to the axles, which in turn transfers power to each rear wheel.
Final Drive Selection
The decision to choose a particular drive mechanism comes down to several key
questions. Which setup is more efficient? How difficult is it to manufacture or obtain
each drive? How easily is it to install on the car? Lastly, what is the weight differential
between each design choice?
The efficiency of a drive system is defined as the ratio of the output over the input
power. V-belts have transmission efficiency of about 95-98% efficiency. After the belt
has installed is begins to wear and begins to slip. As this happens its efficiency
A synchronous belt is made of rubber and steel chords similar to a v-belt. Unlike
v-belts it has molded rubber cogs that prevent it from slipping. The efficiency of this
drive is maintained at about 98%.
Similar to a synchronous belt a roller chain and sprocket setup has an efficiency
of about 98%. A roller chain and sprocket drive experiences an interesting phenomena,
during operation. As the rollers engages and disengages the sprocket at constant angular
velocity, they impart a small jerk. This is known as chordal action, which causes a
variation or ripple in the output velocity. In addition to this chain, belt, sprocket, and
pulley setups cogged or otherwise all create lateral vibration to a certain degree. This is
due to the constant velocity to angular acceleration change that a belt or chain
experiences every time it passes though the pulley or sprocket. Lastly these setups
require substantial structure support. As the sprockets or pulleys transfer power there is a
tendency for them to be drawn or pulled together. The 2004 team experienced this, when
they employed a roller chain drive as their final drive. The end result was a broken out
section of their carbon fiber sub-frame to which the rear sprocket was mounted. The
engine produces a strong tension force in the chain when the car is in operation.
The last setup to be considered is the simple gear train. The overall efficiency of
gear trains is very high. Usually there is only a 1 to 2% power loss per gear set
depending on lubrication, tooth finish, etc. This method is typically the preferred method
of power transfer if the distance between rotating input and output shafts is not too large.
The biggest draw back of using gear trains is they tend to be heavier that other drive
Table B. The decision matrix used to select a final drive.
Drive Mechanisms Efficiency Weight Availability Noise Vibration
Roller Chain and Sprockets 98% 3 3 4 4
Gear Train 99-98% 4 1 2 2
V-belts and pulleys <98% 2 3 3 3
Synchronous belt 98% 2 4 3 4
A decision matrix was used to help the power train sub-team choose a final drive.
Given the parts available, a gear train final drive was on the top of the list. It is the most
efficient means of power transfer, and it produces minimum noise and vibration. The
final drive would also required no additional chassis support structure other than an
encased housing that bolts directly to the side plate. It can easily be coupled to the
torson-gleeson limited slip differential that will be used on the car. This type of
differential is the race industry standard. The torson-gleeson differential can also be
found the Audi Quattro, which is world renown for its traction and rally sport
capabilities. The biggest draw back to the gear train is weight.
Figure 4. Torson-Gleeson limited-slip
differential that will be used in this years
Picture courtesy of Kathy Allman
To make the gear train more competitive the weight issue had to be addressed.
Using a design that had been used in past FSAE teams, the power train sub-team had to
exam if any extra weight could be removed. As is, the gears are solid, bulky and heavy.
The second major problem that needed to be addressed what oil leaks. According
to FSAE rules the car cannot leak any fluids whatsoever or the car will be disqualified
from racing. This was an issue for the 2003 FSAE team. Their final drive design leaked
were it was coupled to the engine’s output shaft. Since our design will be a modified
version of the 2003 team’s final drive we must come up with a solution.
To reduce weight and the rotating inertia of gear train a simple solution was
devised. Remove as much material from the gear as possible. Because the 2003 team
used solid gears, this is possible. Although the gear-face surface area on each tooth must
remain the same, the solid webbing of the gears can be reduced. The exact amount will
have to be careful calculated, because a small safety factor will undoubtedly be used.
The webbing of gears will be trimmed down on a lathe, and next we will use a wire EDM
to cut perpendicular sections from the webbing of each gear in our final drive. To
minimize weight and maximize strength the geometry of these cuts will be impart
determined by examining and benchmarking other gear sets that have similar
performance requirements. This will be a main focus point of next semester’s work. Our
initial estimation of weight reduction is approximately 20%, when compared to similar
modifications done by past Baja teams.
Figure 5. The Honda F-2 motor
connected to a gear set final drive.
Picture courtesy of Kathy Allman
We have also devised two methods of eliminating final drive oil leaks. The first
is to fabricate a simple breather on the top of the final drive housing to prevent a pressure
from build up as the internal parts and lubrication heat up. Secondly, we have
determined how the oil leaks pass the oil seal on the 2003 team final drive. Oil was able
to completely by-pass the seal and leak through the final drive coupler. The coupler
essentially is a sleeve with splines on one half of its outer edge. It mates with the primary
gear of the final drive. The other half of the sleeve’s outer edge has a smooth cylindrical
surface finish protruding though final drive housing. This smooth surface is where the
rubber seal interfaces. The sleeves inter edge mates with the splines of the engine’s
output shaft. Through this inter edge of the coupler is precisely were the oil bypasses the
oil seal and leaks.
The solution is to plug the inter edge of the coupler with an epoxy. With the
addition of the breather, this modification will prevent the oil from being pumped through
the coupler, and leaking on to the ground.
After implementing this design the U of U’s FSAE team stands an excellent
chance of making a good showing at this year’s competition. By using the lessons
learned from past FSAE teams, we have been able to improve upon their designs. The
fuel delivery system, and final drive will have significantly performance modifications,
that should make this year’s power train the best a University of Utah FSAE team has
every been able to produce.
Design of Machinery Robert L. Norton 3rd edition 2004
Honda Service Manual CBR600F3 Honda Motor Co.,LTD December 1994