ENGR 103 Module: Manual Transmission
ENGR
103 – Spring 2012
Engineering
Design Lab III
Lab Section:
003 Date Submitted: 06 / 08 / 12
Group Number:
02
Section Faculty:
Prof. Deepak Siromani
Group Members:
Andrew Carver Chris Otterness Kyle Fitzpatrick
Abstract:
The purpose of this project was to
design, model, and construct a working scaled model of a four-five speed manual
transmission. Along with initial sketches, a completed and functioning
simulation of the transmission using the Pro/E 3D modeling software was produced.
After completion of this model, the file was then sent to a rapid prototyping
machine to produce a 3D prototype of the transmission. This 3D model was then
tested for revolutions per minute for each of its gears, as well as for torque
in its first gear. This project resulted in a four speed transmission that had
a 6.90RPM/Dollar and a 5.76N-m/Dollar efficiency factor for revolutions per
minute and torque respectively. The lowest gear ran at 24RPM and the highest
gear produced around 380 RPM. In the future, adjustments would be made to the
gear shafts and the transmission housing to hopefully produce a much more efficient
system.
Problem
Overview:
The
competition proposed is to design a 4 speed manual transmission that optimizes
power and speed. By applying knowledge of physical concepts such as angular
velocity and torque into the design of the transmission the group aims to
produce the most efficient, powerful and fastest transmission possible. The
competition is based on finding the transmission that produces greatest torque
and also the most speed. The problem that the project is addressing is making
the most efficient transmission possible.
The
constraints for the project are as follows: To design at least a 4 speed manual
transmission designed using Pro Engineer. It must then be tested using the Pro
Engineer software animations. Once tested for functionality on Pro/E, it will
then be printed using a rapid prototyping machine. When assembled the
transmission must fit the pre-made support structure as seen in Figure 1. The
gears also must be compatible by using a Lego NXT motor, to power the
transmission. It will be tested using two criteria; one to see how much torque
the transmission will produce, and two to see how much speed (RPM) the
transmission can produce.
The
budget for this project is being estimated as if it were being made of actual
steel gears and shaft material. The approximate pricing for the materials
needed are as follows: 6 X Steel Bored, 32 Pitch, 40 teeth, Outside Diameter of
1.31”, for $28.51 apiece. 4 X Steel Bored, 32 Pitch, 18 teeth, Outside Diameter
of .63”, for $14.16 apiece. 18 inches of 1/16” Steel Shaft $9.98 [3]. This
would bring the total price up to $237.68. The budget for making the transmission
from the rapid prototype represents how much it actually cost to create the
gears and shafts. The price of the ABS plastic that the printer uses is
approximately $5 per cubic inch. The total amount of plastic used for the
transmission was about 11 cubic inches, bringing the cost up to approximately
$55.
Existing
Solutions:
The manual
transmission has been around for almost as long as automobiles themselves. In
fact, up until 1938 when General Motors started offering automatic
transmissions, all cars had manual gearboxes that required the drivers to
control the gear shifting themselves. The function of any transmission in any
automobile is transferring engine power to the drive-shaft and then to the
wheels. Inside of a transmission there are usually at least four different
gears that when shifted, adjust the vehicle's drive speed and its torque. Lower
gears, which actually have a higher gear ratio, are used to get the vehicle
moving from a standstill. The two main existing manual transmission designs are
the sliding-gear type and the constant-mesh design. The older, now obsolete
design, the sliding-gear type is not used any more in modern cars. The
difference between the two types is that in a sliding-gear type transmission,
the only thing turning at all times is the main drive shaft, which gets shifted
along one axis and at specific points, meshing the gears together and allowing
the car to move. Then, in order to shift into another gear, the main drive
shaft would have to completely disengage with one gear, in order to move on to
the next. The reason why the constant-mesh design transmission is so much more
efficient is that the gears on the main drive shaft are constantly meshed with
the gears on the cluster shaft. The reason that this is possible is because the
gears that are on the main shaft are not directly attached to it and can rotate
freely around it [2]. These transmissions are used very widely in today's
vehicles. Different car companies create their own transmissions and tweak them
in ways that they see fit, but most all manual transmissions today have the
constant-mesh design as a foundation.
Another important concept that is necessary for this project is the idea behind gear ratios. The technical description of the gear ratio of a gear train is the ratio of the angular velocity of the input gear to the angular velocity of the output gear. It can be thought of as how much one gear revolves when the other completes one single revolution. Different gear ratios are important for achieving different gears in cars, allowing for more torque in lower gears by having a higher gear ratio, and more speed in higher gears by having lower gear ratios.
Another important concept that is necessary for this project is the idea behind gear ratios. The technical description of the gear ratio of a gear train is the ratio of the angular velocity of the input gear to the angular velocity of the output gear. It can be thought of as how much one gear revolves when the other completes one single revolution. Different gear ratios are important for achieving different gears in cars, allowing for more torque in lower gears by having a higher gear ratio, and more speed in higher gears by having lower gear ratios.
Design
Objective:
The main goal of this project was to design and build a transmission that would output the most torque and speed. Because half of the competition is based upon the torque that the transmission can withstand the group created a relatively simple transmission that will have fewer chances to catch somewhere and break under heavy force. With torque in mind the group chose to stick to a 4-speed transmission. The group based some of the design on Sariel’s compact gearbox [1]. The compact gearbox was beneficial because it maximizes torque. The formula for torque is the product of force and radius. Because torque relies on radius the thought was that if the group kept the gear shafts short and had larger gears, theoretically it would give more torque in the lowest gear.
High speed was also a major goal for the group. To maximize the speed an efficient system with fitting gear ratios was designed. Smooth transitions from one gear to the next were also an important factor, as rough transitions can easily lead to a broken transmission due to stress. The compact gearbox utilizing multiple shorter, stronger, shafts made this design unique from the standard automotive transmission that has longer linear shafts. Using the unique design of the compact gearbox as a basis the group was able to add modifications to create an even more unique and potentially efficient design.
The main goal of this project was to design and build a transmission that would output the most torque and speed. Because half of the competition is based upon the torque that the transmission can withstand the group created a relatively simple transmission that will have fewer chances to catch somewhere and break under heavy force. With torque in mind the group chose to stick to a 4-speed transmission. The group based some of the design on Sariel’s compact gearbox [1]. The compact gearbox was beneficial because it maximizes torque. The formula for torque is the product of force and radius. Because torque relies on radius the thought was that if the group kept the gear shafts short and had larger gears, theoretically it would give more torque in the lowest gear.
High speed was also a major goal for the group. To maximize the speed an efficient system with fitting gear ratios was designed. Smooth transitions from one gear to the next were also an important factor, as rough transitions can easily lead to a broken transmission due to stress. The compact gearbox utilizing multiple shorter, stronger, shafts made this design unique from the standard automotive transmission that has longer linear shafts. Using the unique design of the compact gearbox as a basis the group was able to add modifications to create an even more unique and potentially efficient design.
The
two main deliverables for this particular project included: an assembly drawing
of our transmission drafted in Pro-Engineer that properly animates the
processes of the transmission. It also must give calculated data on the
theoretical output of the transmission for each gear ratio. The second
deliverable was the actual printed and assembled prototype. The prototype
must have been capable of syncing with the NXT motor and then tested for torque
and speed.
Technical
Activities:
The first week of lab consisted of assembling the team and creating our blog. After starting the blog and receiving the rest of the information about the completion and constraints, more research needed to be done. Throughout the end of week two and into week three we took our ideas and the research that had been completed and put it all into our project proposal. Also in week three a sample gear was made using a tutorial with Pro/E (Figure 2). During the next few weeks, Pro/E started to play a larger role in the project.
The first week of lab consisted of assembling the team and creating our blog. After starting the blog and receiving the rest of the information about the completion and constraints, more research needed to be done. Throughout the end of week two and into week three we took our ideas and the research that had been completed and put it all into our project proposal. Also in week three a sample gear was made using a tutorial with Pro/E (Figure 2). During the next few weeks, Pro/E started to play a larger role in the project.
Figure 2 -
Sample gear created in Pro/E
During week four, the actual design of the transmission was decided on. This included thinking about how many gears and shafts were going to be used, as well as how the shifting would take place. When designing the transmission, the research that had been done on gear ratios had to be taken into account in order to ensure that we ended up with the most efficient gears possible.
Figure 3 – Sketch of the transmission design
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After seeing the results from the simulation it was determined that the amount of force that the gears would be experiencing would be nowhere near the level that would give reason to worry about the teeth breaking. In Pro/engineer with the analysis it was possible to see where the most amount of stress on the gear tooth would be. This is visible as the dark red section in Figure 4 above. In week six we moved on to creating the complete Pro/E model and animation of our transmission system as seen in Figure 5 below.
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Testing/Results:
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GEAR
1
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GEAR
2
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GEAR
3
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GEAR
4
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RPM
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24
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64
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172
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380
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The completed transmission (Figure 6) was assembled to be
test the RPMs of each gear, as well as the torque of the first gear. In order
to have our gears mesh correctly, we had to remove our output shaft and instead
held the gear mounted to the touch sensor up to our fourth shaft to measure the
RPM for each gear.
Table 1 – Results of the RPM test
Table 1 – Results of the RPM test
Using the gear ratios for each gear, a set of theoretical
RPM was determined given the fact that the NXT motor was rotating at 150 RPM.
These theoretical yields could then be compared to the experimental yield in
order to determine how sound our calculations and transmission was.
--GEAR ONE – Projected Gear Ratio – 8.33:1
--GEAR ONE – Projected Gear Ratio – 8.33:1
Theoretical RPM – 18
Experimental RPM - 24
--GEAR TWO – Projected Gear Ratio – 3.33:1
Theoretical RPM – 45
Experimental RPM - 64
--GEAR THREE – Projected Gear Ratio – 1:1
Theoretical RPM – 150
(NXT Input)
Experimental RPM – 172
--GEAR FOUR – Projected Gear Ratio – 1:2.70
Theoretical RPM – 405
Experimental RPM - 380
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After completing the RPM test, the transmission was set-up for testing torque. This was another problem area that arose. Due to the fact that there was no set way for testing torque of these transmissions, a last minute concept had to be designed on the spot. An elbowed piece was attached onto the final gear shaft as seen in Figure 7 below. This piece was used to attach the hanging weights to in order to measure the power of the system. The distance used in the torque calculations was from the second elbow in the piece.
--GEAR ONE TORQUE--
Mass – 0.125kg
Distance from rotational axis – 4.70cm
Acceleration due to Gravity – 9.81m/s2
Torque = (0.125kg) x (4.70cm) x (9.81m/s2) = 5.76 N-m
(As a comparison, the NXT motor was outputting 16 N-m of torque.)
After gathering these results, the efficiency of the
transmission per dollar was calculated.
RPM – 380 rpm (max.) / $55 (cost) = 6.90 RPM/Dollar
TORQUE – 5.76 N-m / $55 = 0.105 N-m/Dollar
TORQUE – 5.76 N-m / $55 = 0.105 N-m/Dollar
Future
Work:
After completing this project, many things have become
apparent to the group as potential areas for improvement as well as other
changes that could be made to the project as a whole in the future. As far as
this particular transmission goes, if it were to be printed a second time, a
few changes would be made. Firstly, in the Pro/E model, the provided Lego NXT
pieces would be used to build the actual housing for the simulation. This would
lessen the chance of incorrect measurements and calculations. Another problem
that arose in the torque test was bowing of the shafts, causing some of the
meshing gears to come apart from one another. This is the reason that the
torque of the system was so low. In the future, much thicker shafts would be
used so that they would not bend. Ideally, this whole system would be made of
metal in order to get the most efficiency out of it. There are also some
improvements that can be made on the project in general, as other groups may
have experienced similar problems. The first being how much simpler designing a
transmission system would be if a matching housing could be designed as well.
In the case of this project, each group had a very different design and it may
have been easier to design, assemble and test these transmissions if they had
their own custom housing. This would also remove the confusion involved with
the torque test. Each group could be required to find their own way to test the
torque from the start. Other than some of these minor problems, this project is
a very interesting one that many people will be interested in in the future.
References
[1] Sariel. (2010). Lego 4-speed compact linear gearbox
[online].
Available:
http://www.youtube.com/watch?v=xISN9U56yBY&feature=related
[2] Cook. (2009). Manual Transmission Basics [online]
Available: http://www.edmunds.com/car-technology/manual-transmission-basics.html
Available: http://www.edmunds.com/car-technology/manual-transmission-basics.html
[3] Carr. (2012). McMaster-Carr [online].
Available: www.mcmaster.com
Available: www.mcmaster.com
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