university of cincinnati - OhioLINK Electronic Theses and

UNIVERSITY OF CINCINNATI
Date: October 31, 2006
I, Ryan Lake_________________________________________________,
hereby submit this work as part of the requirements for the degree of:
Master of Science
in:
Mechanical Engineering
It is entitled:
Integration of a Small Engine Dynamometer into an Eddy Current
Controlled Chassis Dynamometer
This work and its defense approved by:
Chair: Dr. Randall Allemang___________
Dr. David Thompson_____________
Dr. Jay Kim
_
_______________________________
_______________________________
Integration of a Small Engine Dynamometer into an
Eddy Current Controlled Chassis Dynamometer
A thesis submitted to the Graduate School
of the University of Cincinnati
In partial fulfillment of the
requirements for the degree of
MASTER OF SCIENCE
In the Department of Mechanical, Industrial, and Nuclear Engineering
of the College of Engineering
2006
By
Ryan Douglas Lake
B.S., University of Cincinnati, 2004
Committee Chair: Dr. Randall Allemang
Committee:
Dr. David Thompson
Dr. Jay Kim
Abstract
The task of tuning an engine from scratch can be very time consuming and difficult if the
right equipment is not utilized. Several different types of dynamometers with feedback
control systems exist that enable a tuner to simplify the process. However, most of these
systems are designed for specific applications and engines. Typically, the proper equipment
is determined based on the budget and requirements of the tuner. The most common engines
for Formula SAE (FSAE) cars are usually motorcycle engines or something similar. Unlike
the usual car engines, which have separate transmissions, these engines and transmissions are
built together. A complete custom engine dynamometer stand and corresponding connection
between the transmission output shaft and the dynamometer is necessary.
Different types of dynamometers were researched to determine their pros and cons. The
nine inch Land and Sea water brake absorber and dynamometer stand utilized by the
University of Cincinnati’s FSAE team since 1998 was researched to determine its
performance characteristics. The Mustang Chassis Dynamometer and corresponding eddy
current absorber purchased in 2003 were researched as well. The eddy current absorber is
capable of maintaining low RPM speeds compared to the water brake. This key feature could
be taken advantage of if a connection system is developed to utilize the eddy current absorber
in the chassis dynamometer as the absorber for the engine dynamometer. Various designs
were investigated and evaluated. The details of these designs and the pros and cons of each
setup are discussed. The final design was tested and utilized for tuning the 2006 FSAE
engine saving a significant amount of time and effort. During this testing period, small
problems with the system arose and were corrected as they surfaced. The system is still in a
state of testing, and recommendations are presented that will enable a final setup to be
permanently installed.
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Acknowledgments
I would like to extend a great deal of thanks to three groups of individuals: my
committee members, my colleagues in SDRL and Bearcat Motorsports, and my family,
without your support I would not have been able to complete my research and this thesis.
First, I would like to express my sincere appreciation to my advisor, Dr. Randy
Allemang. I can not thank you enough for your continued assistance and input into the
development, review, and completion of this thesis. In addition to the support for my
thesis, the opportunity to work with you as a teacher assistant for the Auto Design I, II,
and III courses during the 2005 and 2006 academic years has been exceptional. The
position not only provided me with the funds to live during the time, but enabled me to
further develop my leadership, team work, and vehicle design skills. The time I spent
with the FSAE program is invaluable to my personal and professional development.
To my other committee members, Dr. David Thompson, and Dr. Jay Kim, I truly
appreciate your assistance and input enabling me to complete this thesis.
To my colleagues in SDRL and Bearcat Motorsports, your academic support and
assistance in reviewing, and suggesting changes to improve the quality of my thesis are
greatly appreciated. I wish all of you the best of success in the remainder of your
academic and professional careers. Thanks to the Bearcat Motorsports organization for
the use of the engine and chassis dynamometers and to the 2005 and 2006 team members
for their assistance in tuning and operating the dynamometers, especially to Dave Moster,
Jeff Kenney, and Greg Curlin for their time spent helping develop and test my thesis.
Last and most important, to my family, especially my wife, Stephanie, I could not
have completed this thesis and masters degree without your endless love and support.
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Table of Contents
TABLE OF CONTENTS .......................................................................................................iv
LIST OF FIGURES.................................................................................................................v
LIST OF TABLES..................................................................................................................vi
LIST OF ACRONYMS.........................................................................................................vii
CHAPTER 1: BACKGROUND.............................................................................................1
1.1 PURPOSE OF DYNAMOMETERS ........................................................................................1
1.2 HISTORY OF DYNAMOMETERS ........................................................................................3
1.3 WATER BRAKE DYNAMOMETERS ...................................................................................6
1.4 ELECTRICAL DYNAMOMETERS .....................................................................................10
CHAPTER 2: UNIVERSITY OF CINCINNATI’S FSAE DYNAMOMETERS............15
2.1 NINE INCH LAND AND SEA WATER BRAKE ABSORBER ................................................15
2.2 MD-95 MUSTANG CHASSIS DYNAMOMETER ...............................................................20
CHAPTER 3: COUPLING THE ENGINE TO THE CHASSIS DYNAMOMETER ....24
3.1 DIRECT DRIVE DESIGN .................................................................................................26
3.2 GEARBOX DESIGN .........................................................................................................30
3.3 CHAIN AND SPROCKETS DESIGN ...................................................................................32
CHAPTER 4: OPERATING THE CHAIN AND SPROCKETS DESIGN .....................37
4.1 INITIAL BREAK-IN .........................................................................................................37
4.2 TUNING ..........................................................................................................................38
4.3 OTHER ISSUES ...............................................................................................................42
4.4 THE CORRECT EDDY CURRENT ABSORBER .................................................................47
CHAPTER 5: CONCLUSIONS AND FUTURE RECOMMENDATIONS ....................50
5.1 CONCLUSIONS................................................................................................................50
5.2 FUTURE RECOMMENDATIONS .......................................................................................54
REFERENCES ......................................................................................................................57
APPENDIX A: DYNAMOMETER COMPARISON .......................................................59
APPENDIX B: MD-95 CHASSIS DYNAMOMETER SPECIFICATION.....................61
APPENDIX C: TELMA CC 80 RETARDER SPECIFICATIONS ................................62
APPENDIX D: F4I REDUCTION/SPEED TABLES .......................................................69
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List of Figures
FIGURE 1: ROPE BRAKE (A) PRONY BRAKE (B).................................................................... 3
FIGURE 2: COMPUTER AND REAL-TIME CONTROL SYSTEM DYNAMOMETER ...................... 5
FIGURE 3: WATER BRAKE DYNAMOMETER CROSS-SECTION ............................................... 6
FIGURE 4: TYPICAL PERFORMANCE CURVES FOR A WATER BRAKE DYNAMOMETER .......... 9
FIGURE 5: PERFORMANCE CURVES: DC OR AC DYNAMOMETERS...................................... 11
FIGURE 6: EDDY CURRENT DYNAMOMETER CROSS SECTION AND END VIEW ................... 13
FIGURE 7: PERFORMANCE CURVES FOR EDDY CURRENT DYNAMOMETER ......................... 14
FIGURE 8: OUTER CASING, INTERNAL ROTOR, BEARING, AND SEAL ................................. 15
FIGURE 9: PICTURE OF THE WATER BRAKE BEARINGS, LEVER ARM, AND LOAD CELL ..... 17
FIGURE 10: NINE INCH WATER BRAKE PERFORMANCE CURVES VS. MEASURED CURVES . 18
FIGURE 11: 2005 FSAE CAR ON MD-95 CHASSIS DYNAMOMETER ................................... 22
FIGURE 12: ACTUAL 2005 TORQUE CURVE VS. DESIRED TORQUE CURVE ......................... 24
FIGURE 13: TOP AND REAR VIEW OF DIRECT DRIVE POTENTIAL SETUP ............................ 27
FIGURE 14: ISO VIEW OF DIRECT DRIVE POTENTIAL SETUP ............................................. 28
FIGURE 15: TOP, FRONT, AND ISO VIEW OF GEARBOX POTENTIAL SETUP ........................ 31
FIGURE 16: TOP, FRONT, AND ISO VIEW OF CHAIN AND SPROCKETS SETUP ..................... 32
FIGURE 17: SPLINED ADAPTOR AND SPROCKET ................................................................. 33
FIGURE 18: CHAIN ROUTING .............................................................................................. 35
FIGURE 19: CHAIN TENSIONING BOLTS ............................................................................. 35
FIGURE 20: CHAIN ANCHOR ............................................................................................... 37
FIGURE 21: PERFORMANCE ELECTRONICS FUEL TABLE, 0 TO 12,000 RPM....................... 42
FIGURE 22: ARROW ON ROTOR .......................................................................................... 43
FIGURE 23: LEVER ARM ALTERATION ............................................................................... 46
FIGURE 24: K-40 PERFORMANCE CURVES VS. MEASURED CURVES................................... 48
FIGURE 25: CC 80 PERFORMANCE CURVES VS. MEASURED CURVES ................................. 49
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List of Tables
TABLE 1: WATER BRAKE PERFORMANCE CURVE SEGMENT DESCRIPTIONS ........................ 9
TABLE 2: DC OR AC PERFORMANCE CURVE SEGMENT DESCRIPTIONS ............................. 11
TABLE 3: EDDY CURRENT PERFORMANCE CURVE SEGMENT DESCRIPTIONS ..................... 14
TABLE 4: METHODS FOR DETERMINING EQUIVALENT INERTIA IN POUNDS ....................... 21
TABLE 5: MAJOR PROS AND CONS OF EACH DESIGN .......................................................... 36
TABLE 6: ROLL TO ENGINE RPM CONVERSION VALUES ................................................... 39
TABLE 7: LEVER ARM MODIFICATION ............................................................................... 46
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List of Acronyms
AC – Alternating Current
AFR – Air to Fuel Ratio
DC – Direct Current
ECU – Engine Control Unit
FSAE – Formula Society of Engineers
MPH – Miles per Hour
RPM – Revolutions per Minute
TP – Throttle Position
VAC – Volts Alternating Current
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Chapter 1: Background
1.1 Purpose of Dynamometers
The main purpose of a dynamometer is to absorb energy. This energy is delivered in
a rotational form and is transferred from the energy source using a driveshaft or other
type of mechanical system. To absorb energy, the rotation must have resistance. If
instrumentation is utilized that measures the rotational speed (tachometer) and the
resistance force (load cell) at a distance from the center of rotation, many parameters
related to the energy source can be calculated. Revolutions per minute (RPM), torque,
and horsepower are three significant parameters. The RPM can be determined directly
from the tachometer and any relevant gear reductions. The torque can be determined by
the load cell value and the distance from the center of rotation. The raw horsepower is
linearly related to RPM and torque. To get comparative values of horsepower,
corrections for temperature and humidity must be taken into account.
Engine, chassis, and shock dynamometers are the most common types used today.
An engine dynamometer is used to tune or test an internal combustion engine. A chassis
dynamometer can be used in the same fashion; however it is capable of also testing
driveline performance, mileage accumulation, and many other characteristics. This is the
most popular use and will be the background for this thesis. The average person will
never need to use or own a dynamometer. However, to any person or organization that is
concerned with making modifications to their vehicle or engine in order to produce more
power, a dynamometer provides a simple way to determine how the modifications
improve performance. A simple five to ten second pull on a dynamometer before and
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after the modifications are made, will be able to answer that question. This information
is crucial to the avid weekend racer and to professional race teams world wide.
Engine dynamometers are not only useful for determining the benefit of upgrading
engine components, but also for generating an entire timing and fuel map for the
vehicle’s Engine Control Unit (ECU). Most engine dynamometers are capable of holding
a motor at a certain speed, utilizing a feedback control process, while modifications are
made to the ignition and fuel map to either produce a desired air-fuel-ratio (AFR) or to
achieve the maximum amount of torque and horsepower. Original equipment
manufacturers, race teams, and after market manufactures specifically will conduct this
type of tuning and testing on their engine systems on an engine dynamometer. As the
name implies, an engine dynamometer is used to tune just the engine, no transmission or
other driveline components are used, meaning the parasitic losses are at a minimum.
Once an ignition and fuel map are generated and the motor is installed into the
automobile, a chassis dynamometer can be used to determine many other parameters:
efficiency of the drive train system, estimated fuel economy, emissions, acceleration, and
reliability to name a few. Dynamometers are very important tools that are used for many
different types of applications related to the internal combustion engine. Without the use
of dynamometers, the advances in engine performance would not be as simple to test
and/or verify the overall effect that an added component contributes.
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1.2 History of Dynamometers
There are many different types of dynamometers that are used around the world today
including hydraulic, electrical, frictional, air brake, and hydrostatic. Different variations
of some of the dynamometers are available. Hybrids have also been developed; one
example is an electrical and hydraulic dynamometer connected together in series. One of
the earliest type of dynamometer to be developed, called a rope brake, relied solely on
friction between a rope and a drum. The drum was attached to the power source and the
frictional force was regulated by adding or subtracting weights. See Figure 1a below. [1]
This dynamometer was invented and used in the earlier part of the 19th century. “Its
successor, the Prony brake, also relied on mechanical friction and like the rope brake
required cooling by water introduced into the hollow brake drum and removed by a
scoop.”[1] Figure 1b shows a typical Prony brake. [2]
a
b
Figure 1: Rope Brake (a) Prony Brake (b)
The first water brake dynamometer was developed by William Froude in 1877.
Within four years of the invention, “Heenan and Froude was established and produced
the first commercial dynamometers.” In 1952 the first rolling test rigs, an early form of
chassis dynamometers, were produced. In 1976, “Consine Dynamics [supplied] the first
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direct digital controlled, DC Chassis Dynamometer with full road load simulation. In
1983, Consine Dynamics joined Froude Engineering Ltd. to form Froude Consine. This
merger expanded the company product range to include ‘state of the art’ vehicle test
chassis dynamometers with digital controllers.” [3] In 1985, a United States Patent was
published that described the invention of an eddy current absorption unit that was to be
used to measure torque from an engine. [4] The Dynojet Research company invented the
“first single roller, inertia, chassis Dynamometer for motorcycles in 1989” [5]
Modern advances in technology, including the use of computers and feedback control
systems, have significantly impacted the capabilities of dynamometers. The computers
provide a method of interaction between the operator and the dynamometer. Parameters
that are desired, typically horsepower, torque, speed, AFR, plus many more are easily
displayed, logged, and saved to a file for easy accessibility. Operational parameters can
also be inputted into the computer and in return will interact with the control system that
regulates the dynamometer. For example, if there is a particular speed that the operator
needs to maintain while a certain engine parameter, such as fuel and/or timing is changed,
that speed can be entered into the computer and would become an operating parameter
for the control system of the dynamometer. The software that communicates with the
dynamometer’s control system varies from each manufacturer. However, most have the
same general concept and once trained on one, other company’s software should be easy
to learn.
Control systems that are used for operating the dynamometers have been developed
over the past 20 years and are available in both open and closed loop form. “In openloop mode, the dynamometer control is set to a percentage of available dynamometer
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output or load. In this mode, the resulting load is independent of throttle position (TP),
RPM, or vehicle speed.” [5] When operating in closed loop mode, which is more
commonly used, a constant speed can be maintained during changes in TP. When this
happens, the load that is applied to the dynamometer is changing with the change in TP.
The closed loop control system monitors the load and the speed. It counteracts the
change in TP by increasing or decreasing the amount of load necessary to maintain the
desired speed. The computer and control systems can be used on most types of
dynamometers. However, the effect of the computer and control system depends on the
type of dynamometer that is used. The diagram below shows a chassis dynamometer that
utilizes a computer and real-time control system during operation. [6]
Figure 2: Computer and Real-Time Control System Dynamometer
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1.3 Water Brake Dynamometers
The hydraulic dynamometer, more commonly known as the water brake, uses water,
a water tight casing, and a rotor that spins inside of the casing. The casing and rotor
represent a pump; however, since the goal of a dynamometer is to absorb energy, they are
designed to be inefficient water pumps. The energy absorbed is converted into heat,
therefore heating the water inside the casing. The water brake is available in various
different configurations, three of which are described in more detail below. A typical
cross section of a water brake is shown below in Figure 3. [7]
Figure 3: Water Brake Dynamometer Cross-Section
The first and most popular water brake dynamometer is commonly referred to as a
variable fill machine. As the name implies, the load is controlled by changing the
amount of water that is inside of the casing. The change is typically controlled with a
valve on the inlet and a separate valve on the outlet side. Needle valves are used instead
of ball valves due to their ability to change the flow rate in minute increments. Loading
is slowly changed by opening or closing the inlet valve, and quickly changed by opening
or closing the outlet valve. This allows small changes in torque resistance by only
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changing the inlet valve. This process is fairly simple and can be done manually by a
person or controlled by a computer to hold back the desired amount of torque.
A second type of water brake dynamometer is called the constant fill machine, or “the
classical Froude or sluice plate design”. [1] With this machine, the load is not changed
by varying the amount of water, but by inserting pairs of thin plates between the rotor and
casing. This reduces the clearance between the rotor and casing therefore increasing the
amount of torque that can be absorbed. The opposite will occur if you remove a pair of
the sluice plates. Each setup is not capable of controlling a large variation in torque, and
to change the amount of torque that it can handle, the unit must be disassembled, and then
reassembled with more plates added, or removed. This is a tedious, manual process that
could take a significant amount of time.
A third type of water brake dynamometer is called a disc dynamometer. The loading
on this machine is controlled by a combination of plates and the amount of water inside
of the casing, similar to the variable fill machine described above. The small clearance
between the plates results in intensive shearing of the water which will resist the applied
torque, and by changing the amount of water with the needle valves; more or less torque
can be absorbed. A small variation in this machine is to have perforated discs instead of
solid discs. This will enable the machine to absorb more torque. Each setup is not
capable of controlling a large variation in torque; however it is more adjustable than the
constant fill machine due to the variable amount of water in the casing. Similar to the
constant fill machine, disassembly and reassembly with inserted plates are required to
change the range of torque that the machine can absorb. Again, this is tedious and time
consuming.
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Water brake dynamometers are considered a low cost machine when compared to
other types of dynamometers that are capable of absorbing the same amount of torque.
Water brake dynamometers are available in many sizes. Water brake absorbers are
available for a shifter cart, which is a high performance go cart that can produce about 30
horsepower, as well as a diesel engine that can produce 2,000 horsepower or more. Due
to this factor, the cost of a water brake dynamometer is going to vary significantly based
on the horsepower requirements. The water brake and a few required components for a
shifter cart cost nearly $4,000 [8] and a diesel engine water brake cost nearly $36,000. [9]
Other instrumentation, which is usually required for accurate and informed tuning, will
add additional costs to these prices.
As with any type of machine, the water brake dynamometer has its limits. Depending
on the particular unit that is purchased, it has a maximum operating speed, and a
maximum amount of power absorption that it can withstand. These two factors also limit
the amount of torque that it can resist. Horsepower is linearly related to speed and torque
as shown in the following equation:
HP =
Torque * RPM
5252
Equation 1: Equation relating horsepower, torque (ft-lbf), and RPM
Based on this equation and testing conducted on individual units, a performance
curve can be developed so that the operating capability of the absorber is identified. An
example of a water brake’s performance curves can be seen below in Figure 4 with a
corresponding description of each line segment in the following table. [1] From this
figure, it is noticeable that the water brake dynamometer is inefficient at low speeds. It is
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difficult for this type of machine to absorb torque and horsepower at roughly 40% of its
maximum speed. This presents problems for tuning engines in the lower RPM ranges.
Figure 4: Typical Performance Curves for a Water Brake Dynamometer
Line Segment
a
b
c
d
e
Description
Dynamometer full. Torque increases with square of speed.
Performance limited by maximum permitted shaft torque.
Performance limited by maximum permitted power.
Maximum permitted speed.
Minimum torque corresponding to minimum permitted water flow.
Table 1: Water Brake Performance Curve Segment Descriptions
Another inefficiency that is important to keep in mind is the slow response of
changing the load. Compared to electrically controlled dynamometers, water brakes
require 10-100 times longer to respond to a 90% change in load. See Appendix A for the
difference between each electrical dynamometer. [10] This is really only a problem when
you do not have a smooth torque curve. For example, when tuning from scratch, or if an
intake is poorly designed such that a large dip or peak occurs, the load cannot be changed
quickly enough to keep the engine from running away from you or nearly stalling out.
This problem can result in longer time spent tuning areas of the ECU map where the
torque increases or decreases rapidly.
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1.4 Electrical Dynamometers
As the classification implies, an electrical dynamometer’s load is controlled by
electricity. Computers and control systems for these dynamometers are necessary to
accurately control the electricity supplied to the machine. Electrical dynamometers can
be one of three types: Alternating Current (AC), Direct Current (DC), or Eddy Current.
Each electrical dynamometer has its advantages and disadvantages which will be
discussed below. See Appendix A for a thorough comparison. [10]
A DC dynamometer is comprised of a DC motor generator that is mounted to a substructure along the axis of rotation. The motor’s outer casing is free to pivot as a means
to transmit resistance torque to a load cell attached to a lever arm. “The rotational speed
of a DC motor is proportional to the voltage applied to it, and the torque is proportional to
the current.” [11] Voltage is linerly related to current and resistance per Ohm’s Law.
V = I *R
Equation 2: Ohm's Law
According to Ohm’s Law, in order to change the torque, i.e. a change in current, the
voltage must be changed. To change the voltage “an electronically-controlled switching
device made of thyristors [or] transistors” [11] is used. The dynamometer’s control
system, including the switching device allows for very quick changes in load. The DC
dynamometer is capable of handling a 90% change in load 50 times faster than the water
brake. A DC dynamometer also has the ability to act as a starter for an engine
dynamometer. This applies to all engines that mount their starters to their transmission’s
bellhousing instead of to the engines themselves. Another benefit of a DC dynamometer
is its ability to produce torque down to zero RPM, also known as stall torque. An
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example of a DC dynamometer’s performance curves can be see below in Figure 5 with a
corresponding description of each line segment in the following table. [1] Compared to
the water brake dynamometer, the DC dynamometer is capable of producing torque much
lower in RPM, providing a broader operational envelope for engine tuning. However, the
DC dynamometer does have its drawbacks as well. Including a high cost per horsepower
capacity, a high rotational inertia, they are relatively large and do not operate well in
higher RPM ranges compared to a water brake with the same power absorbtion capacity.
Figure 5: Performance curves: DC or AC Dynamometers
Line Segment
Description
Constant torque corresponding to maximum current and excitation.
a
Performance limited by maximum permitted power.
b
Maximum permitted speed.
c
Table 2: DC or AC Performance Curve Segment Descriptions
An AC dynamometer is very similar to the DC dynamometer with exception of the
type of motor used and the method of controlling the load. An AC motor is used in place
of the DC motor. “These asynchronous machines consist essentially of an induction
motor, the speed of which is controlled by varying the supply frequency. The power
supply comprises a rectifier, an intermediate DC circuit and an inverter to produce the
variable frequency supply.” [1] The change from a DC motor to an AC motor is
beneficial by reducing the inertia of the system. The AC dynamometer has higher RPM
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capabilities and reacts to the 90% change in load twice as fast as the DC dynamometer,
therefore 100 times faster than a water brake. Other than these differences, the pros and
cons of the DC and AC dynamometers and performance curves are similar.
An Eddy Current dynamometer’s load is not controlled by an electrical motor.
However, it is still classified as an electrical dynamometer because it still utilizes
electricity to control the operation. There are two types of eddy current machines. The
first is cooled by ambient air, while the other is cooled with a closed-loop water system.
As expected the air-cooled system is much simpler to install and to maintain, as well as
less expensive due to the ‘extra’ equipment necessary to operate the water-cooled system.
The air-cooled system is open to the atmosphere while the water-cooled system is
encased similar to a water brake dynamometer. The load on both types is controlled in
the same manner, which “makes use of the principle of electro-magnetic induction”. [1]
A magnetic field that is parallel, but offset, to the axis of rotation is generated by a coil
wrapped around a magnetic pole. These coils are stationary while one or two rotors,
made of ferrous material, are rotated in close proximity of the coils. The rotor is attached
permanently to the shaft that is connected to the power source. Figure 6 below shows a
cross section and end view of an eddy current dynamometer where 40 and 50 are the
rotors, 60 is the coils of wire, and 200 is electromagnets running parallel to rotation. [12]
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Figure 6: Eddy Current Dynamometer Cross Section and End View
When the coils are powered and the rotor is turning, “circulating eddy currents and
the dissipation of power in the form of electrical resistive losses” [1] occur. The
circulating eddy currents generate energy, i.e. heat, and as a result heats up the rotors and
surrounding air. The load is controlled by changing the current that is passed through the
coils. Like the DC and AC systems, the current is regulated with a control system that
enables a response time to a 90% change in load that is 10 times faster than the water
brake; however it is twice as slow as the DC machine, and 10 times slower than the AC
machine. The eddy current machine is also capable of reaching a higher RPM and has a
lower inertia compared to the other electrical dynamometers making it a more viable
option for smaller displacement and horsepower applications that utilize a higher RPM
range. It is also more affordable and smaller than the DC and AC dynamometers;
however larger and more expensive than a water brake. Eddy current machines, like the
water brakes, are not capable of acting as a starter for an engine; therefore an external
starting source is necessary. The eddy current dynamometer is not capable of generating
stall torque like the DC and AC machines, but it is significantly better than the water
brake. A typical eddy current’s performance curves are shown in Figure 7 with a
corresponding description of each line segment in the following table. [1]
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Figure 7: Performance curves for Eddy Current Dynamometer
Line Segment
a
b
c
d
e
Description
Low speed torque corresponding to maximum permitted excitation.
Performance limited by maximum permitted shaft torque.
Performance limited by maximum permitted power.
Maximum permitted speed.
Minimum torque corresponding to residual magnetization and friction.
Table 3: Eddy Current Performance Curve Segment Descriptions
Electrical dynamometers are much more expensive, when compared to a similarly
horsepower rated water brake. The eddy current is the cheapest of the three available,
while the AC and DC are similar in price. For an absorber that can withstand 200
horsepower, a water brake system costs nearly $4,700 [13], while the eddy current costs
$12,950 [14], and the AC costs $49,950 [15]. A water brake system capable of absorbing
1,600 horsepower costs $14,450 [16], while an AC dynamometer capable of absorbing
1,250 horsepower costs $539,500. [15] The prices are for kits that include various
necessary components and software that enable the dynamometer to operate.
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Chapter 2: University of Cincinnati’s FSAE Dynamometers
The University of Cincinnati’s FSAE team owns two different dynamometers. The
first is a nine inch water brake absorber manufactured by Land and Sea that was
purchased in 1998 to be adapted to an engine dynamometer that was built by the FSAE
team. The second is an MD-95 Mustang Chassis Dynamometer that was purchased in
2003 to enable the FSAE team to utilize eddy current control to finalize the custom tuned
maps that are generated on the water brake engine dynamometer.
2.1 Nine Inch Land and Sea Water Brake Absorber
The nine inch Land and Sea dynamometer is designed to be a fast responding toroidal
flow water brake absorber. It is a variable fill type machine that utilizes public water
supply that is regulated through manual load control valve purchased from Land and Sea.
Both inlet and outlet valves are needle valves, which permit small increments in load
change. The rotor inside of the casing is constructed of plastic and is “divided into
pockets by radial vanes set at an angle to the axis of the rotor.” [1] The disassembled
water brake is shown with one of the two outer casings in the following figure.
Figure 8: Outer Casing, Internal Rotor, Bearing, and Seal
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The water brake is instrumented with a water temperature gauge incased in the outer
housing of the dynamometer. This sensor provides the tuner with a reference point as to
how hard the dynamometer is working. From experience, anything under 150ºF is
considered a safe operating range; however most tuning can be completed below 125ºF.
When tuning in the higher RPM range, 12,000 to 15,000, it is hard to apply enough load
without obtaining a temperature between 125ºF and 150ºF. At and above 150ºF, the
grease in the bearings of the absorber begin to liquefy and increasing the risk of damage.
Sealed ball bearings are used in this system combined with radial axle seals. The inner
seal on the bearing is removed and zerk fittings on the casing allow the bearing to be
greased. The grease also acts as a seal for the bearings, so when elevated temperatures
are maintained and grease is lost, it needs to be replaced or bearing and seal failure are
inevitable. Attention to this temperature value is critical to the operation of the
dynamometer. If the temperature continues to rise and reaches 212ºF or higher, there is
no longer water in the absorber, it has turned to vapor. Vapor cannot resist torque, so the
engine’s RPM will increase rapidly, which can damage the engine and the absorber.
The nine inch absorber was purchased to enable the FSAE team to tune Yamaha FZR
600 motorcycle engines. It was later modified to work with the Honda CBR 600 F4 and
F4i motorcycle engines. The transmissions on these motorcycle engines are built
together with the engine as one unit. The water brake’s shaft was not connected to the
crank like a normal engine dynamometer, but to the output of the transmission where the
front sprocket is located. A front sprocket had an adapter plate welded to it that would be
used to connect to a driveshaft.
16
The shaft that the rotor inside of the absorber rotates about is supported with two
flange-mounted Dodge bearings. The end of that shaft has an adapter flange welded on
that allows a driveshaft with two u-joints to be connected between it and the adaptor plate
on the front sprocket. The speed is measured with an encoder wheel and Hall Effect
sensor that is placed between the two bearings. The torque is measured with a load cell
that is attached to a two foot lever arm which is connected to the outer casing of the water
brake. The setup can be seen below in Figure 9. A data acquisition system is used to
record these parameters, as well as exhaust gas, coolant, and water brake temperatures.
Figure 9: Picture of the Water Brake Bearings, Lever Arm, and Load Cell
The engine dynamometer is built to tune motorcycle engines that have the engine and
transmission integrated together. It is built specifically to tune a 1989-1995 Yamaha FZR
600cc four cylinder motor. The stock motor is capable of producing 76 horsepower at
10,000 RPM and 45 ft-lbs of torque at the crank at 8,250 RPM. [17] In this engine, 6th
gear is the highest gear and when engaged a reduction of speed by 1.9, and multiplication
of torque by 1.9. The rev limiter is set at 14,000 RPM, so with the reduction, the
maximum RPM of the engine dynamometer during tuning would be about 7,300 RPM.
17
The peak horsepower is shifted to 5,263 RPM. The peak torque would be at 4,342 RPM
and with the multiplication would rise from 45 to 85.4 ft-lbs.
Like the Yamaha FZR 600cc motor, the Honda CBR 600cc F4i motor is a four
cylinder engine that has an integrated transmission. The dimensions and component
layouts are similar between the two, making the Honda CBR motor a viable replacement
for the out-of-date Yamaha FZR motors. The stock Honda CBR motor is capable of
producing 95.5 horsepower at 12,500 RPM and 42.6 ft-lbs of torque at the crank at
10,250 RPM. [18] Again 6th gear is the highest gear and when engaged it has a reduction
of speed by 2.14, and multiplication of torque by 2.14. The rev limiter is set at 14,500
RPM, so with the reduction, the maximum RPM of the engine dynamometer during
tuning would be about 6,775 RPM. The peak horsepower is shifted to 5,841 RPM. The
peak torque would be at 4,789 RPM and with the multiplication would rise from 42.6 to
91.1 ft-lbs. These values, for both the FZR and CBR engines, are within the absorptive
range of the performance curves for the Land & Sea Water Brake shown in Figure 10.
Figure 10: Nine Inch Water Brake Performance Curves vs. Measured Curves
18
Land & Sea recommends that the dynamometer should not be used for an application
that is near the upper or lower limits of the particular absorber. The operating range that
is utilized for tuning the FZR and F4i engines is in the lower limit of the nine inch water
brake. However, the absorber works well from about 4,000 engine RPM up to redline,
with the exception of areas in the torque curve where there is a sharp increase/decrease.
The reason for the problem is the inability to change the load fast enough to compensate
for the change in torque. The torque and horsepower curves that are generated by the
FSAE tuned engine in 6th gear are shown in the Figure 10 as well. They nearly cross the
capacity envelope of the nine inch absorber at nearly 2,000 RPM, which is approximately
4,000 engine RPM. This confirms the lack of control issues that are prevalent when
trying to tune below 4,000 engine RPM.
In September 2005 the FSAE team upgraded the water brake dynamometer by
purchasing the auto-load control equipment available from Land & Sea. This additional
equipment includes the auto-load control valve, the electrical components that monitor
torque and speed, and a hand-held control interface that is used to input the desired speed
and/or sweep rate. It was not installed during the school year for the 2006 FSAE car, but
should be installed and tested in the fall of 2006 to determine if it functions well for this
application.
19
2.2 MD-95 Mustang Chassis Dynamometer
The MD-95 Mustang Chassis Dynamometer is designed to be used for low
horsepower and low speed testing and tuning. It utilizes an air-cooled eddy current brake
that is capable of absorbing 150 horsepower at speeds up to 80 MPH continuous. It is
also capable of reaching 100 MPH on an intermediate basis, and can measure 200
horsepower. The additional 50 horsepower can be attributed to the inertial acceleration
of the dynamometers rollers. The speed ratings are limited by the bearings that support
the rollers. The complete MD-95 specifications sheet can be viewed in Appendix B.
A chassis dynamometer is used to measure the horsepower and torque generated at
the wheels of a vehicle. This dynamometer uses cradle type rollers, instead of a single
large roller, that are precision machined and dynamically balanced. There are four rolls
total; one for the front and rear side of each drive tire. The rolls connected to the eddy
current absorber are grooved to provide positive traction between the rolls and the tires.
They are connected together with couplers between each roller and between the roller and
absorber shaft. The other rolls are smooth and are not connected together. The
dynamometer is rated at 600 pounds of base mechanical inertia. The eddy current
absorber requires 230 VAC single phase to generate power to the coils. The speed is
measured with an encoder wheel and Hall Effect type sensor that is connected to the shaft
of one of the grooved rolls. The torque is measured with a S-type load cell on a lever arm
connected to the body of the absorber.
The base mechanical inertia is a phrase that chassis dynamometer manufacturers use
to classify the size of the dynamometer and “is a function of the mass and inertia of all
20
the rotating elements of the dynamometer system.” [19] The manufacturers describe the
‘inertia’ of the dynamometers in an equivalent weight, in pounds, to eliminate confusion
in the sales and marketing. The equivalent weight enables a customer to purchase a
dynamometer based on the lightest vehicle that will be tested. The unit of pounds is
much easier for these customers to understand, versus the actual rotational inertia of the
system in lbf-ft-sec2. A dynamometer unit is designed to have a certain base mechanical
inertia. Once built, the unit will be tested to determine the actual base mechanical inertia
to be used in the software to calculate the horsepower associated with accelerating the
inertia. Since the rotational inertia of the system can be calculated based on the design,
the equivalent weight can be determined in two similar methods. These methods are
shown in Table 4 below.
First Method
Relating
Equation
Second Method
I=(W/g)*R2
Roll Radius
(in)
RR
4.2875
Tire Radius
(in)
RT
10
αR=T/I
((4.2875 / 12) * F) / 2.234
System
Inertia
(lbf-ft-sec2)
I
2.234
Roller
Radius (ft)
R
Roll Angular
0.3573 Acceleration
(rev/sec2)
Radius
Constant
C=R2/g
Tire Angular
0.0040 Acceleration αT=(RR/RT)*αR
(rev/sec2)
0.42875 * 0.1599 * F
Equivalent
Weight
(lbs)
W=I/C
Tire Linear
563.044 Acceleration
(ft/sec2)
aT=RT*αT
10 * 0.06857 / 12 * F
F=maT
F=(W / g) * 0.057 * F
Force
Balance
g = 32.174 ft/sec2
Simplified
Equation
Equivalent
Weight (lbs)
(F * g) / (0.057 * F) = W
W=g/0.057
563.044
Table 4: Methods for Determining Equivalent Inertia in Pounds
21
According to Mustang’s recommendations, the weight of the lightest car to be tested
is to be greater than the base mechanical inertia of the dynamometer. The MD-95
Chassis Dynamometer is useful to the FSAE team because the car built by the team is
light weight, about 650 pounds with a driver, and produces nearly 90 horsepower. Since
the dynamometer is built for full-size vehicles and has cradle rollers, the spacing between
the rollers is too large to accommodate the car’s 20 inch diameter tires. The gap is
reduced from 17.25 inches down to 11.625 inches by shifting the smooth rollers closer to
the grooved rollers. The FSAE car is also narrow compared to a full-size vehicle. The
unused portions of the rollers are covered to protect personnel when the dynamometer is
operating. The chassis dynamometer is not placed down in a pit so a ramp is used to get
the car off and on the dynamometer, as well as hold the front wheels elevated to the same
height as the rear wheels during testing. The car is held in place with 2.5 inch wide
heavy duty straps. There are two used in the rear and one in the center holding
backwards, and one or two in the front holding down. The picture in Figure 11 below
illustrates the setup.
Figure 11: 2005 FSAE car on MD-95 Chassis Dynamometer
22
The dynamometer is controlled using the Mustang supplied control panel and
corresponding software. The MDSP 7000 Series Dynamometer Controller Software is
utilized and has many testing and tuning options. An entire manual exists on Mustang’s
website, and there are a few available around with the dynamometer, that is dedicated to
describing all of the software’s capabilities. The testing that is generally conducted on
the FSAE car utilizes the Constant Speed Test and the Power Curve. As the name
Constant Speed Test implies, the car is held at a constant speed while the TP is changed
to allow for final tuning of the engine. The Power Curve test is used to generate
horsepower and torque curves for the vehicle and can be controlled in two different
methods. The first is titled the fixed-sweep-time mode and the second is titled the vehiclesimulation-loading mode. The fixed-sweep-time mode is conducted by entering in a
starting test speed, an ending test speed, and the duration of the test in seconds. The
controller will allow the cars speed to increase one MPH at a time between the starting
and the ending speed. The vehicle-simulation-loading mode is conducted by using the
same values as entered in the fixed-sweep-time mode in addition to the vehicle’s weight,
the power at 50 (MPH), and the simulated inertia. This test will randomly change the
resistance on the dynamometer to vary the speed between the starting and ending speed.
Both tests are typically operated under full, not partial, throttle. This provides the tuner
with the maximum amount of horsepower and torque that the car can generate. Throttle
changes should not be made during testing because it will provide the tuner with corrupt
information about the actual performance of the car.
23
Chapter 3: Coupling the Engine to the Chassis Dynamometer
The troubles experienced with the water brake engine dynamometer during tuning for
the 2005 FSAE car exposed a weakness of the team. This weakness was the long amount
of time that it takes to tune the engine. The intake and exhaust system that was built for
the car was designed to place the peak torque at 8,000 RPM. The design did not take into
consideration torque elsewhere because wave and Helmholtz equations were used to
determine the intake runner length. The resulting torque that was generated from the
built intake did place the peak torque near 8,000 RPM; however, in the RPM range
between 3,700 and 6,700 the torque curve is uneven, as shown in the following torque
curve in Figure 12.
Figure 12: Actual 2005 Torque Curve vs. Desired Torque Curve
At 3,700 RPM the engine produces around 32 ft-lbs of torque. At 5,100 RPM it is
down to nearly 30.5 ft-lbs and then back up to 32 ft-lbs at 5,700 RPM. After that it drops
24
off sharply to 26 ft-lbs at 6,700 RPM and then increases quickly up to 36 ft-lbs at 8,200
RPM. The dip that occurs between 5,700 and 8,200 RPM made tuning the engine very
difficult with the water brake dynamometer. The steep increase and decrease in torque
would cause the engine either to run away from the operator or nearly stall out and die.
After numerous hours were spent trying to tune the 5,700 to 8,200 RPM range of the
map, it was decided that the map was as complete as possible with the water brake. The
map would be finessed on the chassis dynamometer once the car was operational. When
driven for the first time, it was evident that there was a large dip in the torque curve.
When taking off from a stop and accelerating the car would seem to bog down until the
RPM would reach about 7,500 and then the car would accelerate very fast due to the
drastic increase in torque. The car was then placed on the chassis dynamometer hoping
that it would be able to maintain the desired speed to keep the engine from running away
from the tuners. The engines RPM was held at 6,500 in 3rd gear allowing the tuners to try
to work with the fuel and ignition map to fill in sections of the dip. During this testing,
the driver’s back is only about four inches away from the header and the radiator.
Complaints were made regarding the heat after four to six minutes of testing. Once the
car had cooled down, tuning continued on the map where the torque curve was steep.
The chassis dynamometer was capable of holding the car’s speed where desired, allowing
the tuners to quickly make final adjustments to the map in the locations that the water
brake was not capable of maintaining. Small improvements were made in these portions
of the map; however in the end, the map still had the large dip which could not be fixed
with tuning.
25
With the ability to quickly tune the sections of the map on the chassis dynamometer
where it was difficult with the water brake, the desire arose to utilize the chassis
dynamometer as an engine dynamometer. The problem and origination of this thesis is
how to design and integrate the output of the transmission on the engine to the eddy
current absorber.
Even though the project would result in the integration of the two dynamometers, the
need to quickly operate each system independently was still required. In order to
preserve this ability of independent operation, serious modifications to both the engine
and chassis dynamometers were not practical. Restricted modifications were those that
either permanently disabled one of the systems or required a significant amount of time to
reassemble to its original configuration. This included repositioning the components’
locations on the engine dynamometer and the removal of one or more of the chassis
dynamometer’s rollers.
3.1 Direct Drive Design
Solid models of both the chassis and engine dynamometer were generated in Solid
Edge®. With the above limitations in mind, the investigation began by maneuvering the
solid models of each system in an assembly to determine possible configurations that
would result in parallel alignment of the transmission shaft and the eddy current absorber.
The first proposed design yielded axial alignment of the transmission shaft and the roller
at the opposite end of eddy current absorber on the chassis dynamometer. The bottom of
the chassis dynamometer frame was supported by 3.5 inch square blocks. This places the
26
center line of the chassis dynamometer’s rollers and eddy current absorber about 10.75
inches above the ground. As built, the engine dynamometer places the center line of the
transmission shaft at nearly 18.25 inches above the ground.
The sub-frame that holds the engine on the engine dynamometer frame is held in
place with four bolts. It is easily removed once the four bolts holding the driveshaft to
the transmission is detached. When removed and placed directly on the ground, the
center line of the transmission shaft would be at 10.75 inch, which would line up
perfectly with the chassis dynamometer’s rollers. An adaptor flange would need to be
manufactured to enable the use of the existing driveshaft utilized for the water brake
system. A hole would need to be cut in the end of the chassis dynamometer frame to
accommodate the driveshaft. A Solid Edge® assembly was generated to show how this
potential design would be setup. Pictures from the assembly are shown in Figure 13 to
help visualize this setup.
Figure 13: Top and Rear View of Direct Drive Potential Setup
A bracket to prevent relative motion between the chassis dynamometer frame and the
engine sub-frame would need to be built and allow linear adjustment in both vertical and
front-to-rear directions and rotational adjustment to enable parallel alignment. Fine
27
adjustment would be necessary to prevent misalignment, therefore vibration, of the
output shaft and the end of the roller. It would be difficult to create a simple bracket that
would permit this type of adjustment. An additional picture, shown in Figure 14, shows a
close-up of the design. The engine sub-frame sits below the chassis dynamometer frame,
which complicates the installation of a simple bracket for adjusting the rotational
alignment. A significant amount of design work would be necessary to develop this
bracket, in addition to manufacturing and installation.
Figure 14: ISO View of Direct Drive Potential Setup
However, in order to accomplish this setup other considerations had to be taken into
account. Since the engine sub-frame would be removed from the engine dynamometer
frame, the existing wiring and data acquisition harnesses would not work, as well as the
radiator. Adding length to both wiring harnesses and routing new coolant lines would be
simple and relatively inexpensive. The extra wiring could be wound up and the old
28
coolant lines reinstalled when returned to the original configuration. A more expensive
option, though not as logical, would be to use a separate radiator and separate harnesses
for the proposed design, leaving the engine dynamometer untouched except for the
removal of the driveshaft and the four bolts holding down the sub-frame.
Another concern is the high rotational speeds that would be prevalent with the direct
drive of the eddy current brake. The chassis dynamometer’s maximum continuous speed
is 80 MPH. With the 8.575 inch diameter roller, this correlates to a maximum of 3,135
RPM. This maximum RPM limits the continuous operational RPM range in each gear.
The entire engine RPM range can be tuned in 1st gear. In 2nd gear the engine can only
reach about 11,500 RPM, and in 3rd only about 9,000 RPM. A spreadsheet that compares
the crank’s RPM to the transmission’s output shaft RPM in each gear is located in
Appendix D.
Though this design seems practical, sustained high speeds and the necessity to
remove the engine sub-frame, which also required additional wiring and coolant system
modifications, prompted the need for a different design. The new design would simplify
the process of switching back and forth between each engine dynamometer setup and
reduce the high rotational speeds.
29
3.2 Gearbox Design
After further study, a second design was developed that counteracted the issues that
arose from the first design. Instead of directly connecting the transmission shaft and the
roller, a gear box would be utilized to reduce the rotational speed. Commercially
available units were deemed too expensive and in most cases too large for the power
capacity required. The FSAE team had spare parts from old engines, so the gears that
were used in the transmission for 2nd gear, which is a 2.063 reduction, were used to
develop a small, simple gearbox that would be manufactured. In this design, the
connection between the output of the transmission and the end of the roller involved a
few steps. Instead of removing the engine sub-frame and the hassle of the wiring and
cooling components, the removal of the water brake from its shaft would be necessary.
This can be done with a bolt and wrench in about five minutes. The water brake would
be replaced with a coupler that would connect to the input shaft of the gearbox. The
gearbox would be secured to the water brake sub-frame at a location that would place the
output of the gearbox at a 12.75 inch height. This is the same height as the rollers with
the chassis dynamometer sitting on top of with 3.5×5.5 inch blocks, with the 5.5 inch
dimension in the vertical direction. The existing casters would need to be replaced with
shorter ones, with shims to provide small height adjustment. A similar bracket, as
described in the previous design, would be needed to restrain the engine dynamometer
frame and still allow adjustment. Again, similar problems exist with this bracket that was
present in the Direct Drive design, though a less elaborate design would work because the
frames are closer together. Adaptor flanges would need to be manufactured for the
30
output shaft of the gearbox and the end of the roller. Another driveshaft with two Ujoints would need to be built to connect the system together. A Solid Edge® assembly
was generated to show how this potential design would be setup. Pictures from the
assembly are shown below in Figure 15 to help visualize this setup. Notice that this
configuration utilizes the main engine dynamometer frame and therefore the existing
radiator and all electrical components.
Figure 15: Top, Front, and ISO View of Gearbox Potential Setup
Compared to the first design, instead of only being able to tune throughout the entire
RPM range in 1st gear, now it is possible in every gear except for 6th. Also, other than the
simple removal of the water brake from the shaft, no modifications to the engine
dynamometer would be necessary. The Gear Box design met the desired goals, however
in the process, the complexity increased significantly and the time commitment required
in manufacturing all of the one-off components increased. Again, a design that was
simpler was desired.
31
3.3 Chain and Sprockets Design
A third idea, which was intended to reduce the amount of manufacturing time, was to
replace the gearbox with a chain and sprocket. This third idea was short lived because it
prompted the final design that was built.
The third design is the simplest and most feasible design that was developed. As
stated, a chain and two sprockets are utilized in a similar method as on a motorcycle. A
stock front sprocket would be installed on the output shaft of the transmission. A rear
sprocket would be connected to the one of the grooved rollers on the chassis
dynamometer. The Solid Edge® assembly pictures in Figure 16 shows the setup.
Figure 16: Top, Front, and ISO View of Chain and Sprockets Setup
32
To connect the rear sprocket to the roller a couple of ideas were investigated. The
first was to bolt the sprocket to the end of the roller. This placed the roller and chain
really close to the bearing support for the roller. A second design involved an adaptor
that bolted to the end of the roller, but spaced the sprocket away from the bearing
support. The third idea, which was utilized, used the uniform grooves on the roller as a
spline. A ¾ inch thick steel adaptor is used that has a water jetted spline pattern on the
inside diameter to hold the sprocket in position. The sprocket is held to the adaptor with
six 5/16 inch bolts. The roll to sprocket adaptor is shown in Figure 17.
Figure 17: Splined Adaptor and Sprocket
The adaptor is split into two halves. There are two reasons for splitting the adaptor.
The first, and most important, is to prevent the sprocket from moving. A bolt on each
side is used to hold the halves together once installed over the grooved rollers. When
tightened down, the sprocket does not move. The second is to allow for alignment
adjustment. When the two bolts are loose, the adaptor can be shifted along the grooved
roller axially to facilitate the planar alignment of the front and rear sprocket. Also, when
loose, the sprocket can be checked for trueness. A dial indicator is used to verify that the
sprocket is turning true in the axial direction, meaning no wobbling, and can be adjusted
with a soft tipped hammer. The radial trueness is adjusted by loosening the six bolts that
33
hold the sprocket to the adaptor. The holes in the sprocket are oversized to 3/8” to allow
for this adjustment. The trueness is adjusted with shims and is verified with a human eye
and a reference point. Once adjusted, the bolts are retightened and the trueness is
checked again in both directions. A long straight edge is used to verify that the rear
sprocket and front sprocket are in the same plane. The closer the sprockets are to being
in the same plane results in a longer life of the chain and sprockets. However, like the
axial alignment required in the other designs, this does not have to be perfect and is
capable of withstanding minor misalignment.
To make this design work, no modifications to the engine dynamometer are
necessary. However, the upper and lower scatter shields that surround the driveshaft
must be removed. The driveshaft, which is held in place with four bolts on each end,
must also be removed. Next, the engine needs to be slid as far backwards in the
adjustment grooves as possible. Finally, the rubber mounts between the engine subframe and the main dynamometer frame need to be removed and hard mounted. All of
which can be done in about twenty-five to thirty minutes. The adaptor that is used to
connect the transmission shaft to the driveshaft is replaced with a stock front sprocket.
An opening in the back of the chassis dynamometer frame is used to run the lower section
of the chain through. The cutout was located incorrectly when it was made, but was fixed
by elevating the chassis dynamometer frame up an additional two inches. It is now
supported with 3.5×5.5 inch blocks, with the 5.5 inch dimension in the vertical direction.
The top of the chain is high enough that it clears the top side of the chassis dynamometer
frame shown in Figure 18. Instead of using similar brackets that were discussed in the
other two designs, two ½ inch bolts are used. See Figure 19 below. Not only does this
34
connect the two dynamometers together, but also permits linear adjustment needed to
tension the chain. Small angular adjustment is also possible which enables parallel
alignment of the rollers and output shaft of the transmission.
Figure 18: Chain Routing
Figure 19: Chain Tensioning Bolts
A 55 tooth sprocket made for a 525 pitch chain purchased from Sprocket Specialists
is utilized. This is the smallest rear sprocket that would fit around the roller and splined
adaptor without any interference issues. The front sprocket is from the stock Honda CBR
F4i engine and has 16 teeth. This sprocket combination results in a 3.438 reduction.
This large reduction significantly reduces the high rotational speeds and enables the
freedom to tune the engine in any of the six gears. In comparison to the direct drive
design, instead of obtaining the 3,135 RPM at about 9,000 engine RPM in 3rd gear, now
the speed is only 912 RPM. However, in comparison to the direct drive and the gearbox
designs, even with proper maintenance, the chain will stretch and the teeth on the
sprockets will wear out. In the other two designs, the driveshafts have u-joints which are
lubricated with grease and would last significantly longer than the chain and sprockets.
35
The goal for this project was to determine a method of connecting the University of
Cincinnati’s engine dynamometer to the chassis dynamometer in a design that was quick
and simple. The final design that was used is just that. To provide an overview of the
benefits and drawbacks of each design that was researched, the following table was
generated.
Direct Drive Design
Pros
Cons
Small amount of
manufacturing
High rotational
speeds
Cheap
75 minute
change over
time
Simple
Misalignment
issues
Gearbox Design
Pros
Cons
Slower
A lot of
rotational
manufacturing
speeds
60 minute
Misalignment
change over
issues
time
Chain and Sprockets Design
Pros
Cons
Very little
manufacturing
Chain
breakage
30 minute
change over time
Expensive
Complicated
Simple
Chain and
Sprockets
Wear Out
Expensive
Misalignment is
not a big issue
Much slower
rotational speeds
Table 5: Major Pros and Cons of each Design
36
Chapter 4: Operating the Chain and Sprockets Design
4.1 Initial Break-In
The first time that the Chain and Sprockets design was run; four issues immediately
arose that needed attention. The first involved the rubber mounts from which the engine
sub-frame is mounted. After noticing the engine and sub-frame moving while loaded
with the eddy current, the rubber mounts were removed to create a solid mount to prevent
undesired movement.
Once this problem was solved, another one developed that
was similar in fashion. Since the rubber mounts were
removed and no elastic translation was available, the energy
was then used to lift the front of the engine dynamometer off
of the ground. The logical fix for this issue was to anchor the
front side of the engine dynamometer to the ground. A solid
anchor was considered, however due to the necessity to adjust
the slack in the drive chain, a flexible or adjustable anchor was
required. Turn buckles, which permit adjustment, were
researched and deemed inconvenient due to available lengths
with appropriate load ratings. Two links of chain were used
instead. One end was anchored to the ground while the other
was bolted in tension from the bottom up allowing for
adjustment. One of the chain anchors is shown in Figure 20.
37
Figure 20: Chain anchor
Another problem arose when the drive chain repeatedly required tightening. Upon
further investigation, slotted holes were found on the engine sub-frame that enabled
adjustment for the alignment of the water brake. The bolts were loosened and the engine
was slid as far back as it could go in the slots, then tightened back down.
The fourth problem was the tight and loose spots in the chain. By process of
elimination, the rear sprocket was deemed responsible. The sprocket was visually out-ofround when the roller was spinning. To fix the problem, the bolt holes in the sprocket
were oversized, and shims were inserted between the roller and the sprocket. The reason
behind the problem is one of two, or a combination, issues. The bolt holes in the sprocket
are not concentric with itself, or the bolt holes on the adaptor are not concentric with the
roller. Neither was investigated further since the problem was significantly reduced.
There are still minor tight and loose spots in the chain, but they do not affect the
performance of the dynamometer. Once these problems were repaired, no other issues
developed until later in the tuning process.
4.2 Tuning
The goals when retuning the 2005 intake and exhaust systems were to get
familiarized with the new setup and to obtain a better understanding of the Mustang
Dynamometer software. Before any accurate measurements were taken, the software’s
parameters had to be corrected for the new setup. The first parameter that had to be
changed was the roll diameter.
To determine the torque applied to the roller, the software uses the diameter of the
roller at which the tires apply the force. With the Chain and Sprockets design, the rear
sprocket is larger than the roller. Thus the diameter that the force is applied is increased
from the 8.575 inch roller diameter to the 10.948 inch pitch diameter of the 55 tooth 525
rear sprocket. Also, since no tires are used and the gear ratios and final reduction ratio
are all known, the engine RPM can be accurately calculated from the measured eddy
current RPM using the Roll to Engine RPM Conversion. The correct value, shown in
Table 6 for each gear, must be entered based on which gear is engaged during tuning.
1st
17.748
2nd
12.919
3rd
10.317
4th
8.901
5th
7.972
6th
7.353
Table 6: Roll to Engine RPM Conversion Values
The final parameter that needs to be changed is the equivalent weight, or inertia.
With the Chain and Sprockets setup, a weight of 400 pounds is used. Any significant
value higher than this, such as 450 or more, will result in the dynamometer surging at the
locations of the map where the torque increases sharply. The same happens if the weight
is decreased drastically. This occurs because the design only utilizes two of the four
rolls; therefore the inertia of the chassis dynamometer is smaller than the 600 pounds of
base mechanical inertia. Without the two idle rollers, the Solid Edge® model of the
system estimates that the equivalent inertia should be 390 pounds. This is near the 400
pounds that is physically used during tuning. Other nearby values, ± 25 pounds, can be
tested to see if surging is reduced further, but 400 pounds appears to work well.
Once these values are changed, the software is setup and ready for tuning to begin.
The engine is typically started in neutral and allowed time to reach normal operating
temperature. Once warm, the engine is shutoff and placed into gear. Nearly all of the
39
tuning is conducted in 3rd gear. As stated in Chapter 2 under the Mustang Dynamometer
section, the Constant Speed Test is used. This test is started and conducted in the
following manner. A starting speed is entered. In 3rd gear this correlates to about twelve
MPH. Prior to an additional tuner releasing the clutch, the computer operator will press
the Start Test button and provide a corresponding increase in throttle. The clutch is then
released and the tuning process is underway. The Constant Speed Test allows the tuner to
step up or down by one MPH increments. This correlates to a 312 RPM change at the
crank in 3rd gear. Since the fuel and ignition tables are incremented by 800 RPM (12,000
maximum RPM setup), an change in two, or three MPH is necessary to advance/retard to
the next column of cells.
The large final reduction that the Chain and Sprockets design utilizes results in really
slow rotational speed. Experience has shown that the eddy current dynamometer reacts
to changes in load better when it is rotating faster. Thus, to enable tuners the ability to
easily tune the lower RPM range of the engine, 6th gear is used from about 1,800 to 4,000
RPM. In 6th gear, a one MPH increment correlates to a 227 RPM change at the crank.
Again, since the fuel and ignition tables are incremented by 800 RPM an change in three
or four MPH is necessary to advance/retard to the next column of cells in 6th gear.
While tuning in 3rd gear, the sharp incline in torque caused the eddy current
dynamometer to surge. When the weight parameter was decreased to 400 pounds, the
surging lessened, but was still prevalent. Knowing that the dynamometer reacts better at
faster speeds prompted tuning this area of the map in 6th gear as well. This results in a
40% increase in speed, as well as a 29% decrease in torque that the eddy current must
absorb. The eddy current speed never surpasses 1,700 RPM in 6th gear, which is nearly
40
half of the 3,135 RPM top speed. Instead of producing 484 ft-lbs peak torque, the engine
now produces 345 ft-lbs peak torque. The higher speed and lower torque significantly
reduced the surging that was occurring in 3rd gear and further simplified tuning in the
difficult portion of the map.
As mentioned previously, eddy current dynamometers get hot when they are used
continuously. To assist in maintaining cool conditions, fans are used along with some
homemade ductwork directed at the eddy current absorber. To try to prevent
overheating, the tuning is limited to about eight minutes in the 2,000 to 7,000 RPM range
and lower loading conditions. It is also limited to about four minutes at when exceeding
7,000 RPM and higher loading conditions. This is a general guideline for tuning with the
eddy current absorber, however first hand exposure will provide a better understanding.
Experience has shown that the dynamometer does get to a point where it is too hot and
will not be able to maintain the desired speed. Obviously, when this occurs it is time to
stop tuning and allow the eddy current rotors to cool down. When tuning is to be stopped
it is recommended that the speed be decreased while still running the Constant Speed
Test. Reduce the throttle to about 20% and bring down the speed to about twelve MPH
before the clutch is disengaged. This enables the dynamometer to stop faster and as a
result prevents the chain and transmission from coasting to a stop from high speeds. The
cooling time will vary, depending on how hot the eddy current brake got. In the case
where it gets too hot to hold the desired speed, it should sit for at least 45 minutes with
fans blowing on the absorber. In other instances, 30-35 minutes is sufficient.
41
4.3 Other Issues
As tuning continued, other issues developed including a serious vibration that would
occur above 11,000 engine RPM in 3rd gear, which corresponds to about 34 MPH.
However, the vibration is not prevalent in 6th gear at 34 MPH. It appears that a resonance
occurs between the engine, engine dynamometer, and chassis dynamometer near 11,000
engine RPM. The main cause of the vibration is unknown. However, the chassis
dynamometer is not anchored to the concrete, and this is suspected to be the root cause of
the problem. Once a final layout is determined for the Center Hill facility, the chassis
dynamometer can be anchored down to determine its affect on the vibration.
Unfortunately, the vibration prevented tuning the engine for the 2006 FSAE car
above 11,200 RPM using the Chain and Sprockets design. The ECU’s fuel and ignition
maps ended with two columns of cells at 11,200 and 12,000 RPM. An example of the
fuel table used in the Performance Electronics software is shown in Figure 21 below.
Figure 21: Performance Electronics Fuel Table, 0 to 12,000 RPM
The peak torque had been achieved at 8,500 RPM, and the effect of the restrictor was
linearly reducing the torque at about 1.2 ft-lbs per 500 RPM. To enable the completion
of the table, i.e. the 11,200 and 12,000 RPM columns, an interpolation was performed to
42
generate the values. Once completed, a quick sweep of the 11,200 RPM column was
conducted to verify that the AFR was acceptable. Changes that were made resulted in
corresponding interpolation changes to the 12,000 RPM column. The plan was to later
confirm these values and to continue tuning out to 14,000 RPM on the water brake
dynamometer. This was deemed unnecessary and a waste of time due to data that
showed that while on the course, drivers typically shifted before getting to 10,750 RPM.
Another problem was discovered after the eddy current absorber got red hot after an
extended tuning period. There were arrows cast into the
eddy current rotors indicating the intended rotational
direction, shown in Figure 22. The Chain and Sprockets
design rotated the rollers/rotors in the opposite direction.
As installed in the Center Hill facility, the only way that
a car can be tested on the chassis dynamometer also
resulted in the backwards rotation of the rollers. The
Chain and Sprockets design was based on the
assumption that the rollers would rotate in the same
direction that a FSAE car on the chassis dynamometer
would make them rotate. However, this assumption was
incorrect due to the unintentional installation error. The
Figure 22: Arrow on Rotor
MD-95 spec sheet was compared to the MD-100
Mustang Dynamometer spec sheet. The MD-95 spec sheet, shown in Appendix B, said
that the dynamometer is uni-directional and the front rolls are not coupled to rear rolls.
The MD-100 spec sheet said that the dynamometer is belted for bi-directional capability.
43
Mustang Dynamometer was contacted to verify that no damage was caused to the eddy
current absorber by rotating it in the opposite direction. Technical support verified that
the only difference that makes the MD-95 uni-directional and the MD-100 bi-directional
is the belt that connects the front and rear rolls.
Another small problem that occurred twice was the master link clip breaking.
Luckily the chain never separated sparing catastrophic damage to the engine. The cause
of this is unknown; however the problem could possibly lie in the chain hitting the
diamond plate roll cover and chassis dynamometer frame. This typically occurs at times
when running really rich and other times throughout the tuning process. If this is found
to be the cause a piece, of rubber screwed to the roll cover and dynamometer frame could
help. Always check to make sure the master link clip is still attached after each run.
An additional problem that occurred involved exceeding the maximum output of the
load cell. This had been occurring since the tuning had begun, but was not evident to the
tuners. The testing and tuning of the 2005 intake and exhaust setup, as well as the tuning
for the rebuilt 2004 intake and exhaust setup were all conducted during this time. The
torque curves for these setups had an interesting flat spot between 8,000 and 11,200 RPM
that did not exceed 36 ft-lbs. Once tuning began for the 2006 engine and the same flat
spot occurred, it was predicted that the restrictor was prohibiting anymore power from
being produced. At one point in time, the surging in 3rd gear required the use of 6th gear
to tune the 8,000 RPM column. The maximum engine torque of 36 ft-lbs in 3rd gear all of
a sudden was 45 ft-lbs in 6th gear. The torque curves from each gear agreed except where
the torque superseded 36 ft-lbs. This prompted research into what was causing this
inconsistency. The trace viewer enables the tuner to choose which parameters to display
44
in a graph format. The force measured by the load cell did not surpass 355 lbs. The lever
arm was manually loaded, which confirmed this maximum output. The measured length
of the lever arm is one foot. This results in a maximum torque measurement of 355 ftlbs. With the Chain and Sprockets design, and an approximated 45 ft-lbs of torque at the
crank, the eddy current brake would need to be able to hold back 464 ft-lbs in 3rd gear. In
6th gear, the eddy current brake would need to be able to hold back 331 ft-lbs. Since this
is lower than the 355 ft-lbs rated capacity, the dynamometer was able to provide the
tuners with the correct engine torque in 6th gear and not in 3rd gear.
To fix the problem, a couple of options were available. The first was to change the
ratio of the sprockets used in the Chain and Sprockets design. The ratio would need to
decrease, and since the rear sprocket was as small as possible without causing
interference, then the front sprocket had to be larger. The largest front sprocket available
for the F4i engine has 17 teeth. This would make the reduction ratio change from 3.438
to 3.235. Though helpful (464 ft-lbs would be reduced to 436 ft-lbs), it would not be
enough to still tune in 3rd gear. A second option was to tune everything in 6th gear. This
was possible, but not desirable due to the vibration that was prevalent and the higher
rotational speeds. The third and final option was to extend the lever arm on the eddy
current absorber. Since the absorber was apparently capable of holding back the torque
generated by the engine and existing reduction, this was deemed the viable solution. The
original lever arm was twelve inches long. The only way to accommodate a longer lever
arm, in a short time frame was to extend it to 21.25 inches. This length enabled the load
cell to be directly mounted to the main frame of the chassis dynamometer with minimal
work, and therefore increased the ft-lb measurement capability of the load cell as shown
45
in Table 7 below. Figure 23 shows this modification, in addition to the two posts that
were welded to the new lever arm to allow calibration weights to be easily installed.
They were welded at 15 inches from the center of the absorber, and resulted in a more
accurate calibration than the previous method.
Original
Modified
Lever Arm
Length (ft)
1
1.77
Maximum Measurable
Torque (ft-lbs)
355
628.6
Table 7: Lever Arm Modification
Figure 23: Lever Arm Alteration
Since the engine and the corresponding reduction were producing enough torque to
overload the load cell, a concern developed that the absorber was being overloaded as
well. The following question was asked: Why would a load cell that is only be capable of
measuring 355 pounds be attached to a twelve inch lever arm, if the absorber can hold
back more than that? At the point in time when this occurred, the performance curves for
the eddy current absorber were not acquired. (See next section for further details)
Therefore, the only information available was the maximum 150 horsepower that
Mustang specified on the MD-95 spec sheet. The engine was not capable of producing
more than 95 horsepower, which is about 63% of the rated horsepower absorption.
Taking this into consideration, as well as the fact that the dynamometer had been holding
back the applied load for a couple of hours of testing, proved to be enough information to
continue tuning without damaging the eddy current.
46
4.4 The Correct Eddy Current Absorber
The eddy current absorber that is utilized in the MD-95 Mustang Chassis
Dynamometer is built by Telma, Model CC 80. It has a total of sixteen coils, eight per
rotor which are powered by 24 volts, and has a maximum braking torque of 589 ft-lbs. It
has a maximum rotational speed of 4,500 RPM. These and other technical specifications
can be found in Appendix C.
These specifications explicitly provide the performance curves for the CC 80. When
compared to the specifications from Mustang for the MD-95, they are quite different.
The MD-95 specs out 150 horsepower absorption, while the CC 80 specs out over 450
horsepower. The MD-95 spec sheet also states that it is capable of measuring 200
horsepower. The chassis dynamometer is capable of measuring more than it is capable of
absorbing due to the inertia of the rollers that are accelerated during testing. Despite that,
the difference between the maximum horsepower absorption, and therefore torque
absorption, is substantial.
According to Mustang, the MD-95 was equipped with a K-40 Klam absorber.
However, prior to providing this information, they admitted that in the past poor records
were kept. When the performance curves for the K-40 were received, shown below in
Figure 24, there was an obvious discrepancy between the horsepower and torque that was
actually absorbed by the eddy current during tuning.
47
Figure 24: K-40 Performance Curves vs. Measured Curves
Further research found that the dimensions and the number of coils for the K-40,
compared to the actual eddy current absorber, were drastically different as well. Again,
Mustang was contacted. This time the technical representative said that the eddy current
absorber was probably a K-70, not a K-40. This answer was presented without any
additional investigation. The dimensions and performance curves for the K-70 were
much more consistent with the actually measurements. However, the ‘guess’ provoked a
more detailed search of the eddy current absorber to try to find an identification tag. A
tag was found under the lever arm mounting plate. The information was completely
different than what was previously researched. Instead of a Klam absorber, it said that it
was manufactured by Telma. The information on this tag and the chassis dynamometer
tag can be found in Appendix B. Telma was contacted directly to obtain the performance
curves for their CC 80 model. The performance curves and the measured horsepower
and torque curves from 3rd and 6th gear can be seen below in Figure 25.
48
Figure 25: CC 80 Performance Curves vs. Measured Curves
The graph in Figure 25 depicts an important comparison. In 3rd gear, the measured
torque never surpasses 75% of the available torque. In 6th gear, it never surpasses 53%.
Since 3rd gear uses a higher percentage of the available torque, the dynamometer will
become hotter faster when compared to tuning in 6th gear. Another important factor that
is displayed in this graph is the comparison of the curves generated by 3rd gear and 6th
gear. The 6th gear curve is stretched along the x-axis and compressed along the y-axis
compared to the 3rd gear curve. This is caused by the increased reduction by tuning in 6th
gear versus 3rd gear. It is easier for the software to control the speed and corresponding
load when the rate of change in torque is decreased. This is evident during tuning due to
the decrease in the dynamometer surging in the RPM range where the slope is the largest.
49
Chapter 5: Conclusions and Future Recommendations
5.1 Conclusions
When it comes to motorsports, everyone wants to know how well the engine in the
vehicle performs. The all important horsepower and torque are what the average,
everyday person wants to know when it comes to the vehicle’s performance. They want
to be able to see how a bolt-on part/kit adds to the performance of the engine. In more
cases today, they want to be able to see how changing the fuel and ignition table on their
stand alone ECU affects their horsepower and torque. The larger the number, the faster
they can get from point A to point B. Companies that manufacture, sell, and market high
performance parts for the car enthusiast all compete for the most gain in horsepower and
torque for the money.
Race teams are particular interested in obtaining the absolute best horsepower and
torque curves possible. With the combination of a well-performing engine, and a wellperforming suspension, a racecar should dominate in its race. In order to produce these
optimal curves, engine tuning is a necessity. As presented, there are many choices for the
type of dynamometer that can be used for this process. Each one has its benefits and
drawbacks, including limitations on speed, the ability to quickly change the required
load, and the initial expense. Typically, the more expensive, the better the dynamometer
is overall. Thus, when it comes to choosing a dynamometer, the price is always a large
part of the consideration.
50
Another very important aspect is the control system that regulates the speed and load
of the dynamometer. A feedback control system, though expensive, significantly reduces
the amount of time and effort required to tune an engine. Since time equals money, the
payback period should be reduced with the purchase of the control system.
The University of Cincinnati’s FSAE team is interested in saving as much time as
possible. Time does not necessarily equal money for this organization. However, the
less amount of time spent tuning the engine for the FSAE car results in more practice
time and chances for under-designed components to break prior to attending the collegiac
competition. Using the manual controlled water brake dynamometer to tune the ECU’s
fuel and ignition map has historically prevented the car from finishing at an early enough
date. The purchase of the Mustang Chassis Dynamometer controlled with an eddy
current absorber and the corresponding MDSP 7000 Series Dynamometer Controller
Software provided the team with the benefit of a better dynamometer. However, the
downside to tuning on the chassis dynamometer is the requirement for the car to be
operational. Engine tuning needs to be ongoing while the car is built, not started once the
car is completed. In addition to this, the time spent on the chassis dynamometer is risky
for the driver. The 1,200-1,500ºF header is within inches of the drivers back and is only
isolated from the cockpit by a piece of reflective insulation adhered to a sheet of
aluminum. Also, if the engine were to self-destruct during tuning, the driver is directly
inline with the rotational parts that tend to fail and could be injured. The front tires of the
car are elevated and supported with a ramp. If the straps were to break, or something
similar, the driver could be injured. These reasons are more than enough justification to
restrict this method of complete map tuning from the FSAE program.
51
Since the eddy current dynamometer’s load and speed control capabilities are very
desirable, and it is unrealistic to utilize it continuously in the chassis dynamometer form,
an engine dynamometer setup would be advantageous. This would eliminate the risks
that a driver would be exposed to, as well as eliminate the unnecessary wear and tear on
the cars driveline and tires.
To obtain an engine dynamometer setup in combination with the chassis
dynamometer, various designs were investigated. The Chain and Sprockets design
showed the most promise and simplicity when integrated into the chassis dynamometer.
The design only moderately disables both the engine and chassis dynamometer. When
connected together with this design, the chassis dynamometer can be ready to run in as
little as two minutes, by simply removing the chain. The engine dynamometer, utilizing
the water brake instead of the eddy current Chain and Sprockets design, can be ready to
run in about thirty minutes. First, this requires the removal of the chain and front
sprocket and then the reinstallation of the lower driveshaft scatter shield and front
sprocket adaptor. Next, the engine must be moved forward to its water brake operating
position. Once forward, the rubber mounts can be reinserted between the engine subframe and the main dynamometer frame and bolted down. Finally, the driveshaft can be
reconnected and the upper scatter shield attached prior to hooking up the water supply.
Table 5 provides an overview of the pros and cons of each design that was
researched. Along with the short changeover time discussed above, the Chain and
Sprockets design has important advantages, including misalignment and reduced
rotational speeds when compared to the other two designs. The chain can handle minor
misalignment, and the sprockets provide the speed reduction. The simplistic bolted
52
connection is also beneficial. No brackets are necessary to enable angular alignment
which is required for the Direct Drive and Gear Box designs. A small amount of
manufacturing is required. The splined adaptor and sprocket are the only items that
require any amount of manufacturing.
Even though minor problems occurred with the initial proposed design, small
additions or modifications quickly corrected the issues. Once continuous tuning began
and other problems developed, more changes were necessary to enable accurate tuning.
With the exception of the vibration problem and the cause of the master link clips
breaking, each problem was eliminated. The vibration at the higher RPM ranges did not
prevent the FSAE team from developing a well tuned ECU map. Nearly all of the
engine’s power is below the RPM range in which the vibration is prevalent. In the area
where vibration was a problem, interpolation and in-car testing/confirmation were
sufficient in completing the fuel map.
Dealing with the technical representatives from Mustang can be complicated. They
have a tendency to be vague and do not appear to know what eddy current is installed in
the MD-95 Chassis Dynamometer that the FSAE team owns. The K-40, manufactured
by Klam, was their educated guess. If the chassis dynamometer had a K-40 installed in
it, then it would have never been able to hold back the torque that was generated. When
the specs did not match for the K-40, the K-70 was the next assumption. This too was
found to be incorrect when an identification tag was found on the bottom of the eddy
current absorber and identified it as a CC 80 manufactured by Telma. The dimensions,
number of coils, and other specs for this absorber matched the absorber in the chassis
dynamometer. The performance curves also encased the measured horsepower and
53
torque curves. The absorber is appropriately sized for this application. The upper or
lower limits of its capabilities are exceeded during the tuning process.
The eddy current enables the tuner to hold the engine at a slow speed. The water
brake is inefficient at lower speeds. With the nine inch absorber and in 6th gear, the
output speed of the transmission is slow compared to the limits of the absorber. This
situation makes it very difficult to control the load. The eddy current, though close to its
limits, at slow speeds significantly improves the ability to tune the bottom end of the
map.
5.2 Future Recommendations
The addition of the Chain and Sprockets design, which utilizes the eddy current
dynamometer, to the University of Cincinnati’s FSAE program significantly, reduced the
amount of time required to tune the engine for the team’s cars. However, for the 2006
car’s engine, no tuning was attempted over 11,200 RPM. The chassis and engine
dynamometer would vibrate excessively, and no attempt was made to supersede this
speed. If the chassis dynamometer were to be anchored to the ground the vibration might
be reduced. It was not anchored after it was moved to accommodate the engine
dynamometer’s location for the Chain and Sprockets design. The Center Hill facility is
to be rearranged and a new location for the chassis dynamometer is still undetermined. If
the permanent location has not been finalized by the tuning period for the 2007 FSAE
car, the chassis dynamometer should be anchored down to the concrete regardless.
54
Since vibration is a problem with the Chain and Sprockets setup at 11,000 RPM and
higher, the water brake should be used at these speeds. At the higher speeds the water
brake is advantageous because the torque changes slowly. The automatic load control
that was purchased for the nine inch water brake needs to be installed and tested. If the
auto load control is integrated into the water brake system and functions as advertised, it
will be extremely beneficial. It should reduce the level of expertise and time that is
required to operate the manual control valve to maintain the engine’s RPM.
Rubber padding needs to be installed to keep the chain from hitting the diamond plate
covers and the chassis dynamometer frame. It is believed that this will keep the chain
master link clip from breaking. Always have a few extra around in the event that the
master link clip does break. After each tuning run, check to make sure that the clip is still
present on the master link. If it continues to be a problem, the rivet type, versus the clip
type, master link may be necessary. This will complicate reconnecting the chain and
sprockets because the chain becomes continuous once riveted together. The engine
dynamometer frame will need to be moved closer to the chassis dynamometer using the
chain tensioning bolts. This will allow the chain to be installed around the front sprocket,
which can then be slid onto the transmission output shaft.
Another recommendation is to install some type of temperature probe near one of the
rotors on the eddy current absorber. This will allow tuners to observe the temperature
that the rotors are emitting, and determine what temperature is safe. For example, if the
eddy current brake cannot hold a constant speed at 1000ºF, then they can monitor the
temperature and when it reaches 850ºF or so, tuning can be stopped to allow it to cool
down.
55
To simplify the process of returning the engine to its proper location in the engine
dynamometer sub-frame, some form of adjustable hard mount needs to be added. This
was going to be done when returned to the water brake setup, but it has not been used in
that fashion since tuning began with the Chain and Sprockets design. The re-alignment
of the driveshaft when setting up the water brake dynamometer is described in the
following steps. Locate the marks/indentations where the bolts have been tightened
down in the past. Slide the engine forward in the slots until the bolts line up with the
marks. Once close, connect the driveshaft between the transmission output shaft and the
water brake absorber. Place a dial indicator on the driveshaft between the two u-joints, as
close to the engine as possible. Continue adjusting the engines position until the dial
indicator reads true. Determine some method, probably a bolt and jam nut, which will
provide a positive stop for moving the engine forward anymore. Before anything is
welded, disconnect the ECU.
Finally, a new clutch system needs to be installed. In order to operate the clutch in its
existing location, operators climb over the chassis dynamometer. This is a tripping and
falling hazard, and in an emergency is difficult to access.
56
References
[1]
Plint, Michael and Martyr, Anthony (1999) Engine Testing Theory and Practice.
2nd edition. Woburn, Butterworth-Heinemann.
[2]
The University of Texas at Austin, Department of Mechanical Engineering.
www.me.utexas.edu. ME 224L: Home-Made Prony Brake.
http://www.me.utexas.edu/~lotario/me244L/labs/pmdc/pronybrake.html
[3]
Froude Hofmann. www.froudehofmann.com. About Us: History.
http://www.froudehofmann.com/about_1.htm
[4]
Free Patents Online. www.freepatentsonline.com. Eddy Current Patent.
http://www.freepatentsonline.com/4509374.html
[5]
Dynojet Research. www.dynojet.com. About Us: History.
http://www.dynojet.com/about_us/index.php
[6]
National Instruments. www.zone.ni.com. Achieve Flexibility in Your Automotive
Dynamometer Applications.
http://zone.ni.com/devzone/conceptd.nsf/webmain/D1D95AF0DB0AC49E86256
CCA00514200
[7]
Wikipedia. www.wikipedia.org. Dynamometer.
http://en.wikipedia.org/wiki/Dynamometer
[8]
Land and Sea. www.land-and-sea.com. Kart Engine Dynamometer – Pricing.
http://www.land-and-sea.com/kart-dyno/kart-dyno-price.htm
[9]
Land and Sea. www.land-and-sea.com. Diesel Dynamometer – Pricing.
http://www.land-and-sea.com/diesel-dynamometer/diesel-dynamometer-price.htm
57
[10]
Land and Sea. www.land-and-sea.com. Dynamometer Comparison.
http://www.land-and-sea.com/dynamometer/dynamometer-comparison.htm
[11]
Wikipedia. www.wikipedia.org. Electric Motor.
http://en.wikipedia.org/wiki/Electric_motor
[12]
Free Patents Online. www.freepatentsonline.com. Eddy Current Patent.
http://www.freepatentsonline.com/4937483.html
[13]
Land and Sea. www.land-and-sea.com. PWC Dynamometers - Pricing.
http://www.land-and-sea.com/pwc-dyno/pwc-dyno-price.htm
[14]
Land and Sea. www.land-and-sea.com. Eddy Current Brakes - Pricing.
http://www.land-and-sea.com/eddy-current-dynamometer/eddy-currentdynamometer-price.htm
[15]
Land and Sea. www.land-and-sea.com. A/C Drives and Brakes - Pricing.
http://www.land-and-sea.com/ac_dynamometer/ac-dynamometer-price.htm
[16]
Land and Sea. www.land-and-sea.com. Auto Engine Dynamometers - Pricing.
http://www.land-and-sea.com/dyno/dyno-price.htm
[17]
Heath Agdog. http://heath.agdog.com. FZR – FZR Specifications.
http://heath.agdog.com/fzr/specifications/
[18]
Sport Rider. http://www.sportrider.com. Dynamometer Charts – Honda 2001
Cbr600F4i.
http://www.sportrider.com/bikes/street_bike_dyno_charts
[19]
Mustang Dynamometers. http://www.mustangdyne.com. Contact Us – FAQ.
http://www.mustangdyne.com/faq.htm
58
Appendix A: Dynamometer Comparison [10]
Feature
Water
Eddy
Inertia
Brake
Current
Rollers
Absorbers
Absorbers
Friction
Brakes
Hydraulic AC Motor- DC MotorPumps Generators Generators
High Hp (steady
state) capacity?
Excellent
n/a*
Good
Poor
(cooling
required
Fair
(cooler
required
Fair
Fair
High RPM
capability?
Excellent
n/a
Fair
Good
Poor
Fair
Poor
Low RPM
torque
(steady state)
capacity?
Fair
n/a*
Very Good
Excellent
Excellent
Excellent
Excellent
Stall torque
(0 RPM range)
test capability?
Poor
Fair
(startup
only)
Poor
Good
Good
Stability of
RPM load
control?
Good
n/a*
Very Good
Poor
Fair
Excellent
Very Good
n/a*
Very Good
(less than
0.05
seconds)
Poor
(less than 1.0
seconds)
Fair
(less than
0.75
seconds)
Excellent
(less than
0.005
seconds)
Very Good
(less than
0.01 seconds)
Typical
Good
response time
(less than 0.5
to 90% load
seconds)
change?
Excellent
Excellent
(with encoder) (with encoder)
Testing
simulation
under computer
control?
Good
n/a*
Excellent
Fair
Not typically
available
Excellent
Very Good
Motoring
capability?
requires
separate
motor
requires
separate
motor
requires
separate
motor
requires
separate
motor
requires
separate
motor
Excellent
Excellent
Suitability to
long duration
testing?
Excellent
n/a*
Fair
Fair
(water
cooled)
Good
(with cooler)
Excellent
Good
Ease of engine
starting?
requires
separate
starter
requires
separate
starter
requires
separate
starter
requires
separate
starter
requires
separate
starter
Excellent
Excellent
Hp capacity
vs. weight?
Excellent
Poor
Fair
Fair
Fair
Poor
Poor
Hp capacity
vs. size?
Excellent
Excellent
Fair
Good
Good
Fair
Poor
Portability of
absorption unit
Excellent
Determined
by weight
Fair
Fair
Good
Poor
Poor
59
RPM, Torque, &
Hp Accuracy?
Determined Determined Determined
by Data
by Data
by Data
Acquisition Acquisition Acquisition
Determined
by Data
Acquisition
Determined
by Data
Acquisition
Determined
by Data
Acquisition
Determined
by Data
Acquisition
Data
Repeatability?
Determined Determined Determined
by Data
by Data
by Data
Acquisition Acquisition Acquisition
Determined
by Data
Acquisition
Determined
by Data
Acquisition
Determined
by Data
Acquisition
Determined
by Data
Acquisition
Resistance to
hysteresis
(breakaway
friction)
Good
Excellent
Good
Good
Poor
Good
Fair
Immunity to untrunioned
parasitic drag
losses
Excellent
(if mounted
directly)
Poor
Good
Good
Fair
Excellent
(with in-line
transducer)
Excellent
(with in-line
transducer)
Affordability per
Hp
(steady state)
capacity?
Excellent
n/a*
Good
Fair
Fair
Poor
Poor
Installation
affordability?
Excellent
(if water is
available)
Fair
(if pit or lift
required)
Very Good
(115v AC
required)
Good
(but cooler
required)
Good
(but cooler
required)
Good
(electrician
required)
Good
(electrician
required)
Affordability of
maintenance?
Excellent
Excellent
Excellent
Fair
Good
Excellent
Good
60
Appendix B: MD-95 Chassis Dynamometer Specification
Horsepower
Maximum Speed
Loading
Inertia
Axle Weight
Controls
Rolls
Frame
Lift
Air requirement
Power Req.
Notes
200-hp maximum measurement capability
150-hp maximum absorption
100 mph intermittent
80 mph continuous
Air cooled eddy current power absorber
600 lbs base mechanical inertia
6,000 lbs (2,727 kg) maximum
Pentium based PC control system, MD-7000 Control Platform
Precision machined and dynamically balanced
Front roll set may be grooved horizontally
8.5" diameter balanced rolls
41" face length
26" inner track width
108" outer track width
17.25" roll spacing
Heavy-duty structural steel frame
Between roll lift with integrated lock
80-100 PSI dry, regulated, oil free
115 VAC single phase, 60 Hz, 15 amps (computer)
230 VAC single phase, 60 HZ, 30 amps (dyno controls)
Vehicle restraint kit required
Dynamometer is uni-directional
Front rolls are not coupled to rear rolls
No additional mechanical inertia
Eddy Current Absorber
Identification Plate
Mfg
Telma
Mfg in
Made In France
Model # Type CC 80
Voltage V 24
NOC105996
Code Nº 10 2 104
Mustang Dynamometer
Identification Plate
Mfg Model #
Md-95
Mfg Serial #
18320
Mfg Date
Feb-03
Mystery #
6369
NOTE: It is believed that the horsepower ratings provided in the MD-95 spec sheet
are incorrect. The actual horsepower capacity can be seen in the performance
curves in section 4.4.
Appendix C: Telma CC 80 Retarder Specifications
62
63
64
65
66
67
68
Appendix D: F4i Reduction/Speed Tables
Main
Out
Reduction
Engine Speed
(rpm)
500
1000
1500
2000
2500
3000
3500
4000
4500
5000
5500
6000
6500
7000
7500
8000
8500
9000
9500
10000
10500
11000
11500
12000
12500
13000
13500
14000
14500
Crank
45
82
1.822
1st
12
34
2.833
2nd
16
33
2.063
3rd
17
28
1.647
4th
19
27
1.421
5th
22
28
1.273
6th
23
27
1.174
Final
16
55
3.438
Output Transmission Speed (rpm)
1st
96.84
193.69
290.53
387.37
484.22
581.06
677.91
774.75
871.59
968.44
1065.28
1162.12
1258.97
1355.81
1452.65
1549.50
1646.34
1743.19
1840.03
1936.87
2033.72
2130.56
2227.40
2324.25
2421.09
2517.93
2614.78
2711.62
2808.46
2nd
133.04
266.08
399.11
532.15
665.19
798.23
931.26
1064.30
1197.34
1330.38
1463.41
1596.45
1729.49
1862.53
1995.57
2128.60
2261.64
2394.68
2527.72
2660.75
2793.79
2926.83
3059.87
3192.90
3325.94
3458.98
3592.02
3725.06
3858.09
3rd
166.59
333.19
499.78
666.38
832.97
999.56
1166.16
1332.75
1499.35
1665.94
1832.53
1999.13
2165.72
2332.32
2498.91
2665.51
2832.10
2998.69
3165.29
3331.88
3498.48
3665.07
3831.66
3998.26
4164.85
4331.45
4498.04
4664.63
4831.23
69
4th
193.09
386.18
579.27
772.36
965.45
1158.54
1351.63
1544.72
1737.80
1930.89
2123.98
2317.07
2510.16
2703.25
2896.34
3089.43
3282.52
3475.61
3668.70
3861.79
4054.88
4247.97
4441.06
4634.15
4827.24
5020.33
5213.41
5406.50
5599.59
5th
215.59
431.18
646.78
862.37
1077.96
1293.55
1509.15
1724.74
1940.33
2155.92
2371.52
2587.11
2802.70
3018.29
3233.89
3449.48
3665.07
3880.66
4096.25
4311.85
4527.44
4743.03
4958.62
5174.22
5389.81
5605.40
5820.99
6036.59
6252.18
6th
233.74
467.48
701.22
934.96
1168.70
1402.44
1636.18
1869.92
2103.66
2337.40
2571.14
2804.88
3038.62
3272.36
3506.10
3739.84
3973.58
4207.32
4441.06
4674.80
4908.54
5142.28
5376.02
5609.76
5843.50
6077.24
6310.98
6544.72
6778.46
Engine Speed
(rpm)
500
1000
1500
2000
2500
3000
3500
4000
4500
5000
5500
6000
6500
7000
7500
8000
8500
9000
9500
10000
10500
11000
11500
12000
12500
13000
13500
14000
14500
Corresponding Wheel/Roll Speed (rpm)
1st
28.17
56.35
84.52
112.69
140.86
169.04
197.21
225.38
253.55
281.73
309.90
338.07
366.24
394.42
422.59
450.76
478.94
507.11
535.28
563.45
591.63
619.80
647.97
676.14
704.32
732.49
760.66
788.84
817.01
2nd
38.70
77.40
116.11
154.81
193.51
232.21
270.91
309.61
348.32
387.02
425.72
464.42
503.12
541.83
580.53
619.23
657.93
696.63
735.34
774.04
812.74
851.44
890.14
928.84
967.55
1006.25
1044.95
1083.65
1122.35
3rd
48.46
96.93
145.39
193.85
242.32
290.78
339.25
387.71
436.17
484.64
533.10
581.56
630.03
678.49
726.96
775.42
823.88
872.35
920.81
969.27
1017.74
1066.20
1114.67
1163.13
1211.59
1260.06
1308.52
1356.98
1405.45
70
4th
56.17
112.34
168.51
224.69
280.86
337.03
393.20
449.37
505.54
561.71
617.89
674.06
730.23
786.40
842.57
898.74
954.92
1011.09
1067.26
1123.43
1179.60
1235.77
1291.94
1348.12
1404.29
1460.46
1516.63
1572.80
1628.97
5th
62.72
125.44
188.15
250.87
313.59
376.31
439.02
501.74
564.46
627.18
689.90
752.61
815.33
878.05
940.77
1003.48
1066.20
1128.92
1191.64
1254.36
1317.07
1379.79
1442.51
1505.23
1567.94
1630.66
1693.38
1756.10
1818.82
6th
68.00
135.99
203.99
271.99
339.99
407.98
475.98
543.98
611.97
679.97
747.97
815.96
883.96
951.96
1019.96
1087.95
1155.95
1223.95
1291.94
1359.94
1427.94
1495.93
1563.93
1631.93
1699.93
1767.92
1835.92
1903.92
1971.91