Dalhousie University – Mechanical Engineering
MECH 4010 – Design Project – Winter 2011
Final Report
Design Group number
Group Supervisor
Group Members
Submission Date
12
Dr. Peter Allen
David Thompson
Jonathan Bourget
Duncan Elliot
Andrew Crooks
April 8, 2011
B00515364
B00466200
B00319505
B00515005
Group 12
Design Build Report
November 18, 2010
Contents
DALHOUSIE UNIVERSITY – MECHANICAL ENGINEERING ........................................................................ 1
LIST OF FIGURES .................................................................................................................................................... 3
1.
INTRODUCTION ............................................................................................................................................. 4
1.1. DESIGN REQUIREMENTS .......................................................................................................................................... 4
1.2. BACKGROUND AND PROBLEM DEFINITION .......................................................................................................... 5
2.
FINAL DESIGN ................................................................................................................................................. 6
2.1. MINI BAJA................................................................................................................................................................... 7
2.1.1.
Pedal Assembly
7
2.1.2.
Brakes
8
2.2. BRUSHLESS DC GENERATOR................................................................................................................................... 8
2.3. CONTROLLER: .......................................................................................................................................................... 11
2.3.1.
Data acquisition
12
2.3.2.
Brake Actuation
15
2.3.3.
Wiring
17
2.4. BATTERY................................................................................................................................................................... 18
2.5. AUXILIARIES ............................................................................................................................................................. 18
3.
SAFETY ........................................................................................................................................................... 20
4.
TESTING PERFORMED .............................................................................................................................. 21
4.1. BENCH TOP TESTING .............................................................................................................................................. 21
4.1.1.
The Apparatus
21
4.1.2.
Labview and Calibrating
22
4.1.3.
Brushless DC Generator
24
4.1.4.
Brushless DC Results
24
4.1.5.
Conventional Automobile Alternator
25
4.1.6.
Alternator Results
27
4.2. COMPARISON ........................................................................................................................................................... 27
4.3. BAJA SYSTEM TESTING (STATIONARY) ................................................................................................................ 28
4.4. REVIEW OF BAJA SYSTEM, VARYING BATTERY CAPACITY ................................................................................. 31
4.5. BAJA SYSTEM TESTING (DYNAMIC) ...................................................................................................................... 34
4.6. LOADS ON A VEHICLE .............................................................................................................................................. 34
4.7. COMPARISON OF ELECTRICITY PRODUCERS ........................................................................................................ 35
4.8. BAJA SYSTEM TESTING............................................................................................................................................ 35
5.
GANTT CHART ............................................................................................................................................. 42
6.
BUDGET ......................................................................................................................................................... 43
7.
CONCLUSION AND RECOMMENDATIONS ........................................................................................... 44
APPENDIX A - DRAWINGS ................................................................................................................................ 45
Dalhousie Univ. – Dept. Of Mechanical Eng.
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Group 12
Design Build Report
November 18, 2010
List of figures
Figure 1 – Completely functional mini baja .................................................................................................. 6
Figure 2 – Master cylinders mounted in the Baja ......................................................................................... 8
Figure 3 – Generator mounted to the frame and driveshaft ...................................................................... 10
Figure 4 – BLDC Generator.......................................................................................................................... 10
Figure 5 – The controller mounted on the frame, on the engine side of the firewall ................................ 11
Figure 6 - Voltage divider circuit ................................................................................................................. 13
Figure 7 - The current monitoring circuit .................................................................................................... 14
Figure 8 - The layout of the AD8205 differential amplifier ......................................................................... 14
Figure 9 – Batteries contained in battery box ............................................................................................ 18
Figure 10 - Bench top Apparatus ................................................................................................................ 21
Figure 11 - Bench top VI – Front and Block View ........................................................................................ 22
Figure 12 - Torque Sensor Calibration ........................................................................................................ 23
Figure 13 - Calibration Constant ................................................................................................................. 24
Figure 14 - Brushless DC Generator Set up and Controller......................................................................... 24
Figure 15 - Brushless DC rad/s and Torque ................................................................................................. 25
Figure 16 - Alternator Apparatus ................................................................................................................ 26
Figure 17 - Wiring the Alternator ................................................................................................................ 26
Figure 18 - Alternator Efficiency ................................................................................................................. 27
Figure 19 - Graph showing different controller settings and different RPM ranges .................................. 29
Figure 20 - Results from mapping the generator set at 10% using the logging equipment ....................... 30
Figure 21 - Results from mapping the generator set at 30% using the logging equipment ....................... 30
Figure 22 - Static testing of the generator with the controller set to 30% max current ............................ 31
Figure 23 - Static testing with high capacity batteries, controller set to 5% max current ......................... 33
Figure 24 - Static testing with higher capacity batteries, controller set to 25% max current .................... 34
List of Tables
Table 1
Specifications supplied with generator .................................................................................... 9
Table 2
showing the resistance chosen for voltage monitoring ......................................................... 12
Table 3
showing current sensing resistances ...................................................................................... 13
Table 4
showing wire gauges for different sections of project ........................................................... 17
Table 1 - Brushless DC Efficiency ................................................................................................................ 25
Table 2 - Alternator Load Example.............................................................................................................. 27
Dalhousie Univ. – Dept. Of Mechanical Eng.
Page 3 of 49
Group 12
1.
Design Build Report
November 18, 2010
Introduction
Design group 12’s objective was to design a system capable of recovering sufficient energy from
braking to run auxiliary systems on a vehicle such as driving lights, interior lighting, stereo system,
HVAC system, engine cooling, fuel system, and power steering. The group implemented a
downscaled version of this system on a vehicle powered by a conventional gasoline engine to
demonstrate concept on a scale reasonable for a senior year design project. The design group used
a brushless DC generator connected to the driveshaft of the vehicle, which charged the batteries.
1.1.
Design Requirements
The group set the design requirements at the beginning of the year for the project as:
Performance
 Generate electricity while braking.
 Generate an amount of energy to power auxiliary equipment proportional to that of a standard
automobile. With the scaling based on the weight of the vehicle.
 Assist mechanical brakes in stopping the scaled down vehicle
Fabrication
 One prototype device will be designed and constructed by the design team
Testing
 Thorough testing will be carried out to evaluate the performance of the system
Funding and Costs
 Funding will be provided to the group by the Dalhousie Mechanical Engineering Department
Property Rights
 The intellectual property developed with this project will belong to the group members. The
Dalhousie Mechanical Engineering Department will own the prototype.
Documentation
 All documentation that is required by the MECH4010/4020 Design course will be submitted on or
before the deadlines.
 Group 12 will create a website to share the projects progress and findings with the public. It will be
run on the provided course server.
Safety
 The building and testing of the device must adhere to the Dalhousie University safety procedures
 All electronics and moving mechanical parts must be contained in a matter that will ensure safety to
the driver and components.
Timeline
 The project team must meet all the deadlines of the MECH 4010/4020 design project class schedule
as outlined in the MECH4010/4020 Design Project Manual
Dalhousie Univ. – Dept. Of Mechanical Eng.
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Group 12
1.2.
Design Build Report
November 18, 2010
Background and Problem Definition
Design group twelve decided that this was a suitable project because of the increasing need for
more efficient vehicles. Many car manufacturers are looking to implement fuel-efficient programs
into their designs. This is due to the decreasing amount of gasoline and oil in the world, and
increased concern over the environmental impacts of fuel consumption. There are many ways to
increase fuel efficiency, many of which have already been explored. Areas such as proper tuning of
the engine and switching from carburetion to port injection and then to direct injection have
increased the efficiency along with the many feedback systems that increase the performance and
efficiency of the engine.
Regardless of how efficient an internal combustion engine operates, there is always energy being
dissipated in the braking process. The kinetic energy of the vehicle is converted to heat by the
friction brakes, hurting the overall energy efficiency of the vehicle. Meanwhile, there is constantly a
parasitic load on the engine in the form of an alternator used to power electrical systems in the
vehicle. As more and more electrical systems are added to modern vehicles, this load continues to
increase. In recent years, research has been in recovering energy lost in braking, also known as
regenerative braking. Substantial technological development has been done in the industry over the
last couple decades, but most of this has been developed for hybrid and electric vehicles. In
comparison, there has been very little done on vehicles propelled solely by a gasoline engine. While
hybrids and electric vehicles are quickly gaining popularity, the group feels that there will always
be a market for gasoline-power-only vehicles. For this reason, the group thought it both relevant
and interesting to investigate the possible gains by generating electricity while braking to power
the electrical loads present in a car.
Dalhousie Univ. – Dept. Of Mechanical Eng.
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Group 12
2.
Design Build Report
November 18, 2010
Final Design
In order to complete the design project objectives, the design was broken down and then discussed
in detailed in the following sections. The design was a down-scaled version of that which would be
implemented on a road vehicle, and was installed on the five year old SAE Baja prototype.
Sprockets were mounted to a shaft which spins 10.75 times faster than the final drive axle, the
sprockets then drive a brushless DC generator. The generator is actuated by a toggle switch or with
the slightest application of the brake pedal and a signal generated by a potentiometer. This
activates the generator controller, and engages the regenerative braking system. The generator
then outputs a current based on the load applied to the generator. The voltage that comes from the
generator is proportional to the speed of the vehicle but also the charge of the batteries. Batteries
designed for electric bikes were used to store the power generated by the system. The design team
also needed to get the Baja vehicle in operating condition which involved a quick mechanical brake
design and wheel change which were imperative to a successful project. The mechanical brakes
needed to be present before any testing could be done and the street tires were added to reduce
rolling resistance, making the vehicle more similar to a typical automobile. A picture of the final
Baja vehicle can be seen in Figure 1.
Figure 1 – Completely functional mini baja
Dalhousie Univ. – Dept. Of Mechanical Eng.
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Group 12
2.1.
Design Build Report
November 18, 2010
Mini Baja
The mini Baja was chosen because it was the closest to being an operational vehicle. It was also
chosen because when scaled down, the amount of energy the team needed to create was within the
means of the provided budget. The team needed to do a fair amount of work to return the baja to
an operational condition which was safe and usable. The following sections outline work that
needed to be done to the baja.
2.1.1.
Pedal Assembly
The existing pedal assembly for the baja had been removed and used for other purposes. The team
managed to find a few of the original parts but ended up fabricating most of the pedal assembly
again. In order to accurately fabricate a pedal assembly the master cylinders needed to be mounted
to line up the shafts. Since the team only had one existing master cylinder with a straight shaft and
it was believed the old master cylinders were no longer working, new ones were ordered. Once the
new master cylinders were acquired they were installed on the existing frame and the brake pedal
was completed.
In addition to the brake pedal a completely new gas pedal needed to be fabricated. A pedal was
made very similar to the style of the brake pedal with some modifications for connection of the
throttle cable and return spring.
The following figure shows the work done to the baja with regards to the pedal assembly.
Dalhousie Univ. – Dept. Of Mechanical Eng.
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Group 12
2.1.2.
Design Build Report
November 18, 2010
Brakes
Combined with the brake pedal assembly new brake master cylinders and brake lines were
required.
New master cylinders were required since the old ones were not functional, the new
master cylinders can be seen mounted in Figure 2. The team found that the brake callipers were
left on the baja but some of the brake lines were taken and not returned. The team went to Strictly
Hydraulics and replaced the missing lines with stainless steel braided lines. This was done because
steel braided lines allow for a much more responsive brake system and it allows for a much more
flexible brake line with independent suspension all around. Once the new master cylinders were
installed, as well as the brake lines, the entire system was bled.
Figure 2 – Master cylinders mounted in the Baja
2.2.
Brushless DC Generator
The group used the Brushless DC 800W Motor from Kelly controllers. This was the only brushless
generator that was found that was within the budget of the project. There was very little
information supplied with this generator, which made finalizing the design of the other components
hard until the generator was acquired and tested. The information that was supplied about the
generator is contained in Table 1. The group was able to assume that the generator would behave
similarly to that of the motor. This assumption was based upon testing done on a brushless DC
motor that was found within the department. From this information the group size the sprockets to
Dalhousie Univ. – Dept. Of Mechanical Eng.
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Group 12
Design Build Report
November 18, 2010
give a one to one gear ratio with that of the drive shaft. The one to one gear ratio results in an RPM
of approximately 3000 at 30 km an hour which was the desired testing max speed.
Table 1
Specifications supplied with generator
Specification
Value
Rated Output
800 W
Rated Voltage
48 VDC
Rated Speed
2500 RPM
No-loading Speed
3100 RPM
Output Torque
3.06 N*M
Efficiency
>85%
Length
123mm
Dalhousie Univ. – Dept. Of Mechanical Eng.
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Group 12
Design Build Report
November 18, 2010
An ‘L’ shaped bracket was constructed out of steel and was mounted on the rear of the Baja as
shown in Figure 3. The drawing for this bracket can be found in Appendix A. Error! Reference
source not found. shows the dimensions of the generator.
Figure 3 – Generator mounted to the frame and driveshaft
Figure 4 – BLDC Generator
Dalhousie Univ. – Dept. Of Mechanical Eng.
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Group 12
2.3.
Design Build Report
November 18, 2010
Controller:
The controller that the design group used was the KBL 48201 from Kelly controllers. The group
decided on a Kelly controller because it was used by a design team several years ago in their design
of a hybrid bicycle. The design team discussed the use of the controller with the hybrid bicycle team
and found out that it was very user friendly. The group specified which Kelly controller to use based
on the generator size and guidance for the manufacturer, Kelly Controllers LLC. The manufacturer
suggests using a controller that is two to three times the rated capacity of the generator. This was
considered when sizing the controller; however, the cost of the controllers also increases
substantially as the rated capacity of the controller increases. Because the generator only operates
in short bursts, the design group specified a controller less than twice the rated capacity of the
generator.
The KBL48201 is a controller that is rated for 100 Amp continuous use at 48 volts and 200 Amp use
for 1 minute. Since the charging periods are brief (2 to 10 seconds), and the controller is rated at
almost twice the capacity of the generator, the controller should never be overloaded.
A picture of the mounted controller can be seen in Figure 5. The controller is located behind the
driver’s left shoulder, on the opposite side of the fire wall.
Figure 5 – The controller mounted on the frame, on the engine side of the firewall
Dalhousie Univ. – Dept. Of Mechanical Eng.
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Group 12
2.3.1.
Design Build Report
November 18, 2010
Data acquisition
To prove that the system was working correctly the group needed to be able to log the power being
produced, as well as how the vehicle was responding to the braking. To monitor the power being
produced the group monitored the voltage across the batteries, current traveling to the lights, and
current coming from the generator. To record how the vehicle responded to the regenerative
braking the group logged the velocity of the vehicle.
All of the data collected was recorded on a MacBook that traveled on the vehicle during testing. The
MacBook ran LabView in Windows 7 with a NI USB-6008 DAQ card connected to it. This was used
to condition the signals that were being received by the different components used to sense the
items listed in the previous paragraph. The VI was design by a group member and will be discussed
later in this section
To sense the voltage across the batteries a voltage divider was used. The voltage divider circuit can
be seen in Figure 6. To size R1 and R2 the group used the equation:
𝑉0 =
𝑅1
𝑉
(𝑅1 + 𝑅2) 𝑖𝑛
The resistances had to be relatively high to limit the amount of current that would flow through
these resistors. 𝑉0 was desired to be approximately 5V at maximum voltage so that the DAQ card
could safely read the voltage. The group used a voltage divider across the entire 24V system, as well
as across one of the 12V batteries. This prevented shorting problems that the group had. The
voltage of the other 12V battery could be found at any time by subtracting the measured value of
the 12V battery from the measured value of the 24V system. Table 2 shows the resistances used for
the voltage monitoring.
Table 2
showing the resistance chosen for voltage monitoring
Expected Max 𝑉0 at
max Power
System
R1
R2
Vin
Voltage
dissipated
24V
1.7 KΩ
9.8 KΩ
30V
4.43V
0.08W
12V
2.35 KΩ
8 KΩ
15V
3.4V
0.02W
Dalhousie Univ. – Dept. Of Mechanical Eng.
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Group 12
Design Build Report
November 18, 2010
Vo
R2
R1
Vin
-
+
Figure 6 - Voltage divider circuit
To sense the current flowing to the lights, as well as from the batteries low side current sensing was
initially used. This technique involved putting a very low known resistance in series with the circuit
that was being monitored. The voltage drop across this could then be read and the current across
the resistor could be calculated. The resistor was set on the low side of the circuit to ensure that the
voltage was with reference to ground for the DAQ card. The resistor values used for this can be
found in Table 3. This approach was successful when monitoring the voltage across the resistors
with a voltmeter, however, when connected to the DAQ card the resolution was not fine enough to
monitor the current.
Table 3
showing current sensing resistances
Power loss at max
System
Resistance
Max Current Expected
current
Generator
12X.04Ω=0.033Ω
30 A
0.25 W
Left light
12X.12Ω=0.01Ω
8A
0.05 W
Right light
12X.12Ω=0.01Ω
8A
0.05 W
Dalhousie Univ. – Dept. Of Mechanical Eng.
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Group 12
Design Build Report
November 18, 2010
Vo
R1
Generator
or Light
Vin
-
+
Figure 7 - The current monitoring circuit
To increase the signal that the DAQ card received the AD8205 differential amplifier was used to
amplify the voltage across the resistors. The group used the chip in a ground reference output
configuration. This means that the reference voltages are set to ground. It entails that with 0100mV range the output of the chip will be 0.05-4.75V. The DAQ card has no trouble sensing these
voltages and thus once of these chips was used when sensing the current to either light or the
generator.
Figure 8 - The layout of the AD8205 differential amplifier
To monitor the velocity of the vehicle an encoder was made using the GP1A57HR and a custom made
encoder disk. The encoder disk was made with 8 slots in it, resulting in 16 pulses per revolution of the
wheel. The encoder disk was mounted to the intermediate shaft between the motor and drive train.
Since the shaft is connected to the wheels using a chain (no slip) the speed of the vehicle is directly
proportional to the speed of the vehicle. The gear ratio between the tires and shaft was measured to be
10.77. This means that the shaft is spinning at 10.77 times that of the wheels, using this and the wheel
diameter the group was able to calculate the speed of the vehicle based on the encoder readings.
Dalhousie Univ. – Dept. Of Mechanical Eng.
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Group 12
Design Build Report
November 18, 2010
To connect the GP1A57HR with the voltage across the infrared light had to be reduced. To do this a
420Ω resistor was connected between the supply voltage from the DAQ card to the infrared light. This
resistor dropped the 5V supply down to an acceptable level for the emitter, ensuring that the emitter
was not overloaded. Initially the photo detector H21LTB was going to be used, however the emitter was
burnt up when the resistor value was not large enough. The group then found the GP1A57HR which had
a larger opening between the detector and emitter, thus was better for mounting.
A picture of the mounter encoder and disk can be seen in
420Ω
Light Detecting
Element
Inferred Light
GP1A57HR
Photo interrupter
INFORMATION REGARDING THE VI
2.3.2.
Brake Actuation
The design group had looked into some different ways of actuating the regenerative brakes. The
controller has two options for actuating the generator. One is based solely on a switch and the
second is based on a switch and varying voltage.
The first option was to activate the generator when a switch is turned on. The controller can then
be pre set to engage the generator anywhere’s from 5 to 50% generator load once the switch is
thrown. This option was used for the initial testing that is discussed later in the report. The group
had planned on setting this switch on a pressure switch that was contained within the brake lines,
thus ones some pressure was placed in the brake lines the generator would engage. However this
switch was found to be seized and a toggle switch was used instead.
For the latter testing the group used a potentiometer that could vary a 0-5 V signal to the generator
based on the travel of the brake pedal. The group used a wire wrapped around a cylinder, attached
to the potentiometer, to sense the linear motion of the brake pedal. Figure___ shows a picture of this
Dalhousie Univ. – Dept. Of Mechanical Eng.
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Group 12
Design Build Report
November 18, 2010
set up. The final design started the generator at a 2 V signal and had a full load on the generator at
2.5V. This narrow range was used so the diameter of the cylinder on the potentiometer could be
larger for ease of machining and attaching to the potentiometer. The 2-2.5 V range was designed to
be fully engaged while the driver was engaging the brake pedal, but before the mechanical brakes
were actuated. This would help ensure that the maximum amount of energy could be recovered.
One problem that was found with the controller was that the varying generator load only works if
the brake switch is activated, the minimum load that can be applied when the switch is activated is
5%, thus when using the varying generator load the generator always has a 5% load on it. This is
very similar to the way the alternator on a regular car works. For this reason, little testing was done
with the varying load. If this design was implemented on a street vehicle the constant 5% would
need to be decreased to a 0% load.
Dalhousie Univ. – Dept. Of Mechanical Eng.
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Group 12
2.3.3.
Design Build Report
November 18, 2010
Wiring
There are multiple connections that required wiring on this project. In most instances the wire
gauge was sized slightly larger than absolutely necessary.
Table 4
showing wire gauges for different sections of project
Connection
Wire Gauge
Max expected
Max expected
(AWG)
voltage
Current
8
30 V
30 A
Batteries to lights
12
15 V
8A
Generator to
12
30 V
30 A
22
5V
mA
22
5V
mA
22
5V
mA
Batteries to
controller
controller
Generator to
controller
Switches to
controller
Sensors to DAQ
The group found that the weakest point in the wiring of the project was the factory wiring from the
generator. These wires are 14 AWG and found to heat up during high loading levels of the generator. If
the project was re-done then a generator with a higher capacity would be used. It is thought that the
significant cost savings on this particular generator were due to the quality and materials used in the
generator.
Dalhousie Univ. – Dept. Of Mechanical Eng.
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Group 12
2.4.
Design Build Report
November 18, 2010
Battery
The batteries that were used on the Mini-Baja regenerative braking system were two abs 12 V, 7 Ah
Lead-Calcium maintenance free batteries. These batteries were used because the group had access
to a supply of these batteries from previous design projects. Using these saved a substantial amount
of money. These batteries were found to be under capacity for the amount of current the generator
was trying to put into them, this was known because the voltage would climb very high during
charging with the generator because the current being fed to the batteries was not being accepted,
thus the current was limited and the voltage increased. If funds allowed and the necessity was
present, the group would purchase batteries with a high Ah ratting. These would accept current
better and would not allow the voltage to spike.
A battery tray was made to hold the batteries in place during testing. This can be seen in Figure 9.
Figure 9 – Batteries contained in battery box
2.5.
Auxiliaries
The main purpose of this design was to generate power to run the auxiliaries in a car. In the scaled
down version two lights were used. These lights were rated at 100 W, running on 12 V. However
the lights were observer to only ever draw approximately 50 W each. The 200W load was scaled to
Dalhousie Univ. – Dept. Of Mechanical Eng.
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Group 12
Design Build Report
November 18, 2010
represent the amount of power that is common in automobile accessories. The lights were wired to
the batteries with a switch to turn them on and off.
Dalhousie Univ. – Dept. Of Mechanical Eng.
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Group 12
3.
Design Build Report
November 18, 2010
Safety
Due to the series of belts and chains operating at high speed and transmitting substantial amounts
of power, the design team took significant precautions to ensure the safety of operator during
testing. All moving parts were encased by belt and chain guards. Furthermore, the drive train and
high power lines were all located behind the driver and separated from the cockpit by the firewall.
This resulted in a relatively safe vehicle for the tests performed.
MORE ABOUT TESTING SAFETY
Dalhousie Univ. – Dept. Of Mechanical Eng.
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Group 12
4.
Design Build Report
November 18, 2010
Testing Performed
4.1.
Bench top Testing
The design group believed it was in its best interest to make a bench top workstation where
different components could be tested before being placed on the Baja. The bench top ended up
having many advantages such as testing many components and concepts before they were placed
on the Baja. The bench top also gave the group the ability to measure the efficiency of different
generators in an attempt to determine the best design. Situated in Dr. Allen’s Laboratory the group
tested a brushless DC generator, a standard car alternator, along with the final generator chosen
and many of the necessary devices required to log the power generated and dissipated by the Baja.
4.1.1.
The Apparatus
The bench top located in Dr. Allen’s laboratory consisted of several components as seen in Figure
10.
Figure 10 - Bench top Apparatus
The system is powered by a brushed DC motor is controlled through a Variac voltage supply and
rectifier. The DC motor is able to produce approximately 250 Watts of rotational power. This was
used to test several generator options. Measuring the current and voltage produced by the motor
and comparing it with the torque and rotational velocity of the input shaft determined the
efficiency of the different generators. The torque is determined with a non-contact shaft-to-shaft
rotary torque sensor with encoder. The model that was used on this bench top was the Futek
TRS605 supplied by Dr. Allen and used by many graduates including Dr. Swan. Much of the
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information used in this apparatus was similar to that used in Dr. Swans masters thesis. The torque
and rotational speed of the input shaft was logged using National Instruments Labview. The Torque
Sensor Datasheet used on the bench top can be found in Appendix B. The efficiency of the motor is
found using the following relation.
𝜂=
𝑂𝑢𝑡𝑝𝑢𝑡
𝑉𝑜𝑙𝑡𝑎𝑔𝑒 [𝑉] 𝑥 𝐶𝑢𝑟𝑟𝑒𝑛𝑡 [𝐴]
=
𝐼𝑛𝑝𝑢𝑡
𝑆ℎ𝑎𝑓𝑡 𝑆𝑝𝑒𝑒𝑑 [𝜔] 𝑥 𝑇𝑜𝑟𝑞𝑢𝑒 [𝑁𝑚]
Two Fluke Multi-meters recorded the power output of the generator. Other components were
necessary depending on the motor in question and are outlined in the following sections.
4.1.2.
Labview and Calibrating
As mentioned previously National Instruments Labview was used to log the torque and rotational
speed of the input shaft. The VI consisted of the encoder and the torque sensor inputs. The NI6008 DAQ card was used to interface the device to the computer. The program’s block diagram seen
in
Dalhousie Univ. – Dept. Of Mechanical Eng.
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November 18, 2010
Figure 11.
Figure 11 - Bench top VI – Front and Block View
The Figure shows two images. The upper Figure is the Front view of the program. This was the user interface that outputted
the measurements. The lower Figure is the Block Diagram. This shows the programming required to take the measurements
and convert the voltages from the DAQ card to the computer. The upper portion of the block diagram counts the falling
edges of the signals and averages them over a set amount of time, this is the method used to determine the shaft speed of
the Generator. The lower portion, of the block diagram, takes the input from the torque sensor signal, averages it and then
signal, averages it and then multiplies by a calibration constant to represents the corresponding Newton-meters. This
Newton-meters. This calibration constant was determined in a separate experiment where several known torques were
Dalhousie Univ. – Dept. Of Mechanical Eng.
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known torques were applied to the shaft. This was done with a linear, rigid member and force spring gauge. This process is
captured in the below
Figure 12
Figure 12 - Torque Sensor Calibration
The equivalent voltages are measured in the VI and a linear relationship was determined from the
responses. The calibration constant was determined by a linear trend line equation generated in
Dalhousie Univ. – Dept. Of Mechanical Eng.
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Excel. The graph in Figure 13 shows this relationship and trend line. The trend line had a Rsquared value of 0.996.
Torque vs Volts
Torque
1.50
y = 0.7252x - 0.0057
R² = 0.9968
1.00
New
0.50
Linear (New)
0.00
0.000
0.500
1.000
Volts
1.500
2.000
Figure 13 - Calibration Constant
The constant was determined to be
4.1.3.
𝑇𝑜𝑟𝑞𝑢𝑒 = 0.7252 ∗ 𝑉𝑜𝑙𝑡𝑠 − 0.0057
Brushless DC Generator
The brushless DC generator that was used was rated for 200W. This was sufficient for our testing
because the torques that would be created were less than the 2 Nm maximum the Torque sensor
could achieve. The generator was connected to the torque sensor with flex couplings. The output of
the generator went through a brushless DC controller, a diode and finally to the battery. The diode
was in place to ensure the motor was not back driven during the testing.
Figure 14 - Brushless DC Generator Set up and Controller
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4.1.4.
Design Build Report
November 18, 2010
Brushless DC Results
The brushless DC generator had a fairly high efficiency in converting the mechanical power to
electrical. This was tested at several rotational speeds. However, due to an overload on the
brushless generator’s controller only some of this data was recorded. This overload on the
brushless controller along with budgetary and time constraints prevented any further testing to
occur.
Figure 15 - Brushless DC rad/s and Torque
The overall efficiency of the brushless DC controller can be seen in the table below.
Table 5 - Brushless DC Efficiency
Input
Rad/s
Torque (N-m)
Power (W)
Output
126.00 Voltage
0.28 Current (A)
35.28 Power (W)
Dalhousie Univ. – Dept. Of Mechanical Eng.
13.29
1.96
26.05
Efficiency
74%
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4.1.5.
Design Build Report
November 18, 2010
Conventional Automobile Alternator
The set up for the alternator is similar to that of the brushless dc. The brushed DC controller is still
the control motor with the torque center mounted between the brushed motor and alternator. The
shafts are all connected with flex-couplings. This apparatus can be seen in Figure 16.
Figure 16 - Alternator Apparatus
The alternator has a rating current of 70 watts. In order to wire the alternator properly electricity
had to be fed to the alternator field and the internal regulator. In order to do this properly the
method was researched on the Internet. The solution was to wire it similar to the below Figure 17.
With the only acceptation being the connection to the field. In this case we used a variable power
supply. This allowed a controlled rate to the field.
Dalhousie Univ. – Dept. Of Mechanical Eng.
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November 18, 2010
Figure 17 - Wiring the Alternator
Multi-meters were placed so that the current and voltage generated by the alternator was
determined. The voltage and current were also determined in several tests.
4.1.6.
Alternator Results
The results for the alternator were very consistent at around 38% efficient. The same procedures
were used when testing the alternator as the brushless DC. Figure 18 shows the efficiencies at
several shaft speeds.
Efficiency
Efficiency (%)
0.6
0.5
0.4
0.3
efficiency
0.2
0.1
0
92
116
201
Shaft rad/s
225
267
Figure 18 - Alternator Efficiency
Dalhousie Univ. – Dept. Of Mechanical Eng.
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The below Table 6 shows an example loading of the alternator the input rad/s and torque along
with the output voltage and current. The efficiency of the alternator was measured to be 38%. With
165 Watts input and 62 Watts output.
Table 6 - Alternator Load Example
Load 3
Input
Output
4.2.
Rad/s
Torque
Power
Voltage
Current
Power
224.61
0.74
165.40
14.41
4.31
62.11
Efficiency
38%
Comparison
There is a significant difference in the efficiencies in the brushless DC generator and the
conventional automotive alternator. This can be due to the large torque required to turn the
alternator when the load is present.
The design group has performed many tests during the completion of this project. The following
sections will outline the results from the testing. This testing involved comparing different ways of
producing electricity from the kinetic energy of the vehicle.
The group found that the most efficient way to produce electricity was to use a brushless DC
generator, the testing procedures and analysis is contained in section 4.7.
Testing was completed to determine the amount of electricity that was required to supply the
electrical demands on a vehicle as well the amount of kinetic energy that is currently dissipated
thorough the heat in brakes. These tests are out lined in section 4.6.
The group also completed testing on the regenerative system that was installed on the Mini Baja
vehicle supplied by the Mechanical engineering department. The testing procedures and that were
used and analysis is contained in section 4.8.
Dalhousie Univ. – Dept. Of Mechanical Eng.
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4.3.
Design Build Report
November 18, 2010
Baja system testing (stationary)
In order to test the generator the group connected the generator to the drive train of the mini-baja,
the generator was coupled to the intermediate shaft within the drivetrain as per the design, but the
chain to the drive axle was decoupled. This allowed for indoor testing of the generator and baja
systems before lugging the buggy down to Port of Halifax for dynamic testing.
With the drive chain decoupled, the mini-baja was wheeled into the welding lab to utilize its good
ventilation and isolation from other workspaces. The first system tested was the kill switch. First it
was ensured that the engine would not fire with the kill engaged, and then that it would shut off
immediately when killed. Once this was established, the throttle linkage and the switches for lights
and generator were tested. Once the operation of basic systems was confirmed, testing was able to
move to the performance characteristics of the generator.
With the generator switched off, the engine was revved to 3000 RPM to simulate driving at 30
km/h (determined based upon final drive gear ratio). When the switch was activated with a
generator load of a given percentage, the drag on the engine was minimal at lower percentages,
with only a little more throttle needed to return the engine speed to 3000 RPM. As the load on the
generator was set to increasingly higher levels, the effect of engaging the generator became more
pronounced as expected, and a considerable amount of throttle was required.
The first testing completed involved taking readings at different RPM ranges at different controller
settings. These were then plotted to help understand how the generator reacts to different speeds.
The graph showing the power produced at the different settings can be found in Figure 19. The
voltage ranged 25-35V, thus current is the dominate factor in the increase power produced which is
desirable for charging the batteries. This data was taking using meters instead of the logging
equipment that was developed since the logging equipment had not been perfected at this time.
Dalhousie Univ. – Dept. Of Mechanical Eng.
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Power
1200
1000
Watts
800
5%
600
20%
400
35%
200
50%
0
0
500
1000
1500
2000
2500
Generator Speed (RPM)
3000
3500
Figure 19 - Graph showing different controller settings and different RPM ranges
It was notable that the readings above were taking at a steady state, opposed to during the inrush of
current when the generator was initially loaded which would have been higher than steady state
values. When the generator was set to full 50% load the engine required a much higher level of
throttle to achieve the same engine RPM.
Once the monitoring systems were completed the group redid the static tests to confirm the
mapping of the generator. The results of some of these tests can be found in Figure 20, and Figure
21, representing mapping 10% and 30% respectively. This data did not lend well to being mapped
using the RPM as the x-axis. This was because the engine RPM was sampling at a rate of
approximately one tenth that of the current and voltage. Thus there were very few data points to
represent the data, and slight amounts of noise drastically changed the appearance of the graphs.
The graphs do still demonstrate that the higher percentage set on the generator does increase the
amount of current produced by the generator.
Dalhousie Univ. – Dept. Of Mechanical Eng.
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Voltage(V) / Current (A)
Generator response 10%
40
30
20
Generator Voltage
10
Generator Current 1
0
-10
0
1000
2000
3000
4000
Engine RPM
Figure 20 - Results from mapping the generator set at 10% using the logging equipment
Voltage (V) & Current (A)
Generator response 30%
50
40
30
20
Generator Voltage
10
Generator Current 1
0
0
1000
2000
3000
Engine RPM
4000
Figure 21 - Results from mapping the generator set at 30% using the logging equipment
If Figure 21 is compared with Figure 22 the data looks much smoother but with some noise, only
the data taken while the switch was activated was used to create Figure 21.
Dalhousie Univ. – Dept. Of Mechanical Eng.
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November 18, 2010
30% Load Static Testing Test
45
350
40
300
250
30
25
200
20
150
15
100
10
rad/s
Voltage & Current
35
Generator Voltage
Generator Current 1
rad/s
50
5
0
0
0
2
4
6
8
10
Time(s)
Figure 22 - Static testing of the generator with the controller set to 30% max current
To summarize the static generator testing, the group found a general idea of what kind of power
could be expected from the generator based on the speed of the shaft (and thus speed of the
vehicle).
Later during testing the controller was damaged and the results from changing the loading
percentage had no affect on the load applied to the generator. Even further in testing the controller
became irresponsive so reprogramming became impossible and testing was executed with the
setting that was stuck on the controller.
4.4.
Review of Baja system, varying battery capacity
The design group had thought that the batteries being used were under sized. The 7Ah 12V
batteries were used because the group had access to them; they fit well into the vehicle, and money
would be saved by not purchasing new batteries.
When the system was being tested and the voltage across the batteries was seen to spike with the
engine RPM the group knew that the batteries were undersized. This was due to the controller
trying to deliver the same amount of power, but the batteries would only accept a limited amount of
current, thus the voltage had to climb with the power. It was still deemed acceptable to use the
undersized batteries for the testing since the testing was going to be brief and the system did not
Dalhousie Univ. – Dept. Of Mechanical Eng.
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have to hold up for a extensive period. Charging batteries at high voltages over their designed levels
will shorten their life. Saving the money on the batteries was deemed worthwhile.
The group did want to see how the system responded when a sufficient power sink was in place. To
do this the group connected one 680Ah 12V battery in series with three 7Ah 12V batteries in
parallel to the charging system and conducted tests with multiple controller settings and ramping
through the engine RPM. This helped map the response of the system with sufficient sized batteries.
It should be noted that during these tests the maximum recordable current is approximately 55
Amps. This was due to the fact that the group did not expect currents over this level so the system
was design with this as the maximum signal, protecting the DAQ card.
The first test completed was a test with the generator set to max current of 5%. The graph for this
data can be found in Figure 23. The regenerative function was continually active during these tests.
The first bump in engine Rad/s demonstrated the inrush current which was read using a meter to
reach as high as 70 A. Inrush current is essentially a shock load to the system. The more meaningful
data is contained within the second data hump. The slow ramping of the engine RPM shows that the
current spikes are far more defined then the spikes in voltage. This is a much better response than
that which is displayed in all other voltage/current graphs within this report.
Dalhousie Univ. – Dept. Of Mechanical Eng.
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Design Build Report
November 18, 2010
Static Testing 5% Load
60
500
50
Generator Voltage
450
Generator Current 1
400
350
300
30
250
rad/s
Voltage & Current
rad/s
40
200
20
150
100
10
50
0
0
0
10
20
30
40
50
Time (s)
Figure 23 - Static testing with high capacity batteries, controller set to 5% max current
The second set of data that will be discussed is located in Figure 24. This data had the controller set
to 25% of maximum load. This data represents the range that the system would be operating while
stopping the Mini-Baja. It is evident that with the larger capacity batteries the voltage is held within
a respectable level for the operating rang. It is notable though that with these larger batteries
charging would only be occurring at revolutions of over 170 rad/s which corresponds to
approximately 17km/h. Even at the maximum voltage of 30V each battery would be charging at
approximately 15V assuming that the batteries were equal size which is a very reasonable charging
voltage.
Dalhousie Univ. – Dept. Of Mechanical Eng.
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Static Testings -- 25 % Load
Generator Voltage
35
400
Generator Current 1
350
rad/s
30
300
250
20
200
15
150
10
100
5
50
0
0
0
10
20
30
40
50
Time (s)
Figure 24 - Static testing with higher capacity batteries, controller set to 25% max current
Something that was observed when doing the larger capacity battery tests was that changing the max
current settings on the controller no longer affected the response of the generator. This is believed to
be attributed to going over capacity during previous testing, and damaging the controller. The controller
would no longer even allow the group to connect to it after the final road tests which were conducted
after the preceding stationary tests. This will be discussed in the following section.
4.5.
Baja system testing (dynamic)
4.6.
Loads on a vehicle
In order to properly determine the specifications of the design several other tests were performed.
These were done specifically for the purpose of the generator decision. Two tests were performed;
one that measured the loads on a car and the other identified the percentage that a typical vehicle
slows down. Both of these tests can be found in the Appendices in more detail.
Dalhousie Univ. – Dept. Of Mechanical Eng.
Page 36 of 49
rad/s
Voltage & Current
25
Group 12
Design Build Report
November 18, 2010
The first test was performed with Dr Swan with the purpose of finding the loads on the car from the
auxiliaries. Several tests were done, however, based on the experiment it was concluded that in
typical driving the auxiliaries use the following:


Voltage: 14V
Current: 48 A
This value included: wipers; high beams; radio; and the fan. The generated power required by the
regenerative braking system was determined from these results. For the scaled down version it was
calculated that 750 Watts were needed to generate a comparable power to that used by the full
scale cars auxiliaries.
The second test was performed to find the amount of braking that was done while driving a specific
route. This was done with advanced logging equipment on a Volkswagen. In the end it was
concluded that 20% of the drive had the ability to generate power either through coasting or
braking. This 20% was used to calculate the previously presented 750 Watt load.
4.7.
Comparison of electricity producers
Tables of RPM/Torque (input) and power output (steady state) at multiple different speeds to show
that we are not just looking at peak operating spots on some motors and bad efficiency spots on
others (which we may end up be doing with the limits of on the motor)
4.8.
Baja system testing
Plots of voltage/current and velocity all on one graph do many stopping rates, start low speeds/low
rates, move to higher speeds and higher decelerations (to show maxing out generator hopefully?)
-do some sort of integration to find POWER produced to batteries p=iv
-Do a p=iv on the “constant” drain from the lights
-do a mv^2 to compare with to see approximate amount of energy that is going to
batteries compared to all other losses (rolling resistance, mech brakes)
-Possibly design a small driving course to simulate a commute. But could also just use
driving simulations and make straight line stops to match the stopping periods (easier and safer i
think....)
-could create a graph with all simulated braking sessions and draining load line to make a
visual representation that people can do the visual “integration” on to see that power in=power out
approximately.
Dalhousie Univ. – Dept. Of Mechanical Eng.
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Design Build Report
November 18, 2010
Dynamic Testing Outline
4.9.
Experimental Determination of Rolling Resistance
In order to isolate the effects of the generator on the deceleration of the mini-baja during testing,
the rolling resistance of the vehicle had to be experimentally determined. The baja is a crudely
constructed off road vehicle which was not designed to operate nearly as smoothly or efficiently as
a normal road car. It’s for this reason that rolling resistance must be carefully considered in order
to be able to extrapolate testing results to normal cars.
To perform this test the buggy was brought up to speed and then allowed decelerating under its
own force.
Figure 25 - Rolling Resistance
The above Figure 25 shows the speed of the buggy in two situations. The red curve shows the speed
of the buggy decelerating under its own force. Corresponding to this is the green plot, which is the
distance, traveled during its stop. The buggy slows from around 10 m/s to stop. The distance that is
required is 90m. The purple plot is the speed of the buggy that is decelerating similar to before
however with the generator was also engaged. The speed from around 10 m/s to stop was
investigated and the blue plot shows its required distance to stop, 40 m.
Dalhousie Univ. – Dept. Of Mechanical Eng.
Page 38 of 49
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Design Build Report
November 18, 2010
As the plot shows, the speed while the buggy decelerates under rolling resistance drops at a
constant rate. This allowed for rolling resistance to be modeled as a constant force acting on the
buggy. Therefore the resistance power, or rate of kinetic energy lost to resistance is equal to …
-
comment on how rolling resistance compares to a normal vehicle
4.10. Generator Performance
The first set of dynamic tests performed involved getting up to speed and then engaging the
generator. The purpose of this is to determine the effects of generator loading on the deceleration
of the vehicle, and to establish how it affects the performance of the regeneration system. It will
also give some idea of what to expect before starting tests using the brake pedal function.
The first test was to determine the generating power when only the generator is engaged.
Therefore, no mechanical brakes were used in the first trial. The buggy was brought up to a predetermined speed of 30 km/h or around 8 m/s. The generator was then engaged and the gas pedal
was released. As Figure 26 shows the current and voltage peaks when the generator is engaged.
50
45
40
35
30
25
20
15
10
5
0
10
9
8
7
6
5
4
3
2
1
0
80
85
90
Time
95
100
Speed (m/s)
Voltage & Current
Dynamic Testing
Generator
Voltage
Generator
Current
Figure 26 - Dynamic Testing only Generator
The voltage peaks at around 47 volts and the current at 35 amps. Therefore the inrush power was
1645 Watts and the breaking lasted about 10 seconds. The graph shows the spikes in current and
voltage. It is very evident that the current contributes to a significant amount of the power
generated. The voltage increases by about 20 volts or approximately double. This is a typically high
Dalhousie Univ. – Dept. Of Mechanical Eng.
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change rate and charging rate of the battery. The reasoning for this is discussed later in the report.
To put this into better perspective Figure 27 shows the speed versus power relationship. The
power generated is correlates very closely to the speed of the buggy.
Figure 27 - Dynamic Testing Power
Several tests were conducted without the mechanical brakes used. All of the data sets were very
similar and all produced the same amount of power. The average power generated was around 681
KW and the total energy generated around 8.2 KJ.
The next tests that were conducted involved using the mechanical brakes in conjunction with the
generator. These were done with the intention of stopping at typical rates that one would see in
normal driving operations. To perform this test several rough distances were used to determine
stopping distance. The Baja would always begin stopping at the same location with the same speed.
The two tests that will be presented in this report involve stopping times of around 5 seconds. In
these tests the mechanical brakes are used in conjunction with the generator. Figure 28 (Trial 1)
and Figure 30 (Trial 2) show two similar brake situations. Trial 2 is traveling at a slightly higher
speed and therefore the inrush current is also slightly higher.
Dalhousie Univ. – Dept. Of Mechanical Eng.
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Figure 28 - Mechanical Brakes Generation Trial 1
Trial 1 initially created 1200 W and over the 5 seconds averaged 600 W of power. This equated to a
total energy of 3.0 KJ. The power generated can be seen in Figure 30. Trial 2 has a similar braking
time of 5 seconds and creates 1400 W of inrush power. This can be attributed to a 0.5 m/s increase
in speed compared to Trial 1.
Figure 29 - Mechanical Brakes Power Trial 1
Trial 2 has a similar braking time of 5 seconds and creates 1400 W of inrush power. This can be
attributed to a 0.5 m/s increase in speed compared to Trial 1.
Dalhousie Univ. – Dept. Of Mechanical Eng.
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Figure 30 - Mechanical Brakes Generation Trial 2
In both trials the mechanical brakes were used to assist in the stop. The lights were also running in
these experiments. The lights use around 200W of power when the generator is loaded.
Figure 31 - Mechanical Brakes Power Trial 2
Figure 31 shows the power that is generated during the stop. When examining both graphs an
average of 692 W was generated and 3.5 KJ of energy was recovered.
Dalhousie Univ. – Dept. Of Mechanical Eng.
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An interesting observation is the voltage effects when the lights are on. The effect is similar to that
when larger batteries are used. The voltage is significantly less and the current is the main power
determinant. There is a large amount of current that is generated.
4.11. System performance with brake pedal
-
Describe Test procedure, data for each test
Data analysis
Present results
Compare with set loads
Dalhousie Univ. – Dept. Of Mechanical Eng.
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5.
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November 18, 2010
Gantt chart
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6.
Design Build Report
November 18, 2010
Budget
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7.
Design Build Report
November 18, 2010
Conclusion and Recommendations
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Appendix A – Rolling Resistance of a Standard Automobile
Testing of decelerations on a standard auto mobile
On November 7, 2010 testing of the deceleration of a standard vehicle was completed. The test site
was a private, relatively flat, straight road. To negate any affects that an incline would have each
test was done in both directions. The vehicle used was a 2004, Volkswagen Jetta Wagon with the
TDI power train.
Three different scenarios were tested. The scenarios were slowing with the clutch disengaged. This
shows the amount of drag of the vehicle without the engine connected to the drive train. The
second test was to decelerate, leaving the clutch engaged, using the engine as a brake and leaving
the transmission in third gear. The last test was decelerating using a standard engine braking
technique, downshifting when the engine RPM dropped to approximately 1500 RPM.
The data has some unexpected blips in it. Some of these resulted in a large puddle that was on the
road. This puddle only affected the first test and was avoided on the following two tests. Ideally this
testing would have been done with a gasoline engine to relate the data closer to the majority of
vehicles.
The first test showed that the time to decelerate due to rolling, air and mechanical drag was
approximately 50 seconds to achieve 10km/h. Slowing to a full stop was not done due to the length
of the road.
Deceleration Clutch Disengaged
60
Heading out of
road
Spped (km/h)
50
Heading into
Road
40
30
20
10
0
0
10
20
Dalhousie Univ. – Dept. Of Mechanical Eng.
30
Time (s)
40
50
60
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The second test showed that the time to decelerate to 20km/h while in third gear was approximately 18
seconds. The vehicle was only slowed to 20 Km/h to avoid stalling the engine.
Decelerating in Third Gear
60
Heading out of road
Speed (km/h)
50
Heading into road
40
30
20
10
0
0
5
10
15
20
25
Time (s)
The third test was to decelerate and downshift as the vehicle slows. Downshifts took place when the
engine RPM reach 1500 RPM. This resulted in slowing to 10km/h in approximately 23 seconds.
Deceleration with normal engine braking
60
Heading out of
road
Speed (km/h)
50
40
30
20
10
0
0
5
10
15
Time (s)
20
25
30
These tests reveal that downshifting while driving slows the vehicle in approximately twice the amount
of time than that of coming to a rolling stop.
Dalhousie Univ. – Dept. Of Mechanical Eng.
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Appendix B – Torque Sensor Data Sheet
Dalhousie Univ. – Dept. Of Mechanical Eng.
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