Design of Alternative Automatic Transmission for Electric Mopeds

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International Journal of Engineering Research & Science (IJOER) ISSN: [2395-6992] [Vol-3, Issue-11, November- 2017]
Page | 46
Design of Alternative Automatic Transmission for Electric
Ameya Bhusari1, Saurabh Rege2
1Department of Mechanical, Maharashtra Institute of Technology, PUNE-38
2Department of Mechanical, Modern College of Engineering, PUNE-05
Abstract The number of automobiles has seen an alarming rise in the recent years. In the year 2014, the number of road
vehicles produced annually increased to 87.23 million vehicles from around 40 million in 2000. This shows that production
has increased to more than twice the volume in only 14 years. This has also caused a rise in the po llution levels. Global CO2
levels are on the rise due to increased pollution, contributing to the greenhouse effect. Hence it is very important to reduce
our dependency on gasoline driven vehicles. Electric veh icles are a good alternative to these. The advent of electric vehicles
is marred by factors like unavailability of cha rging stations and most importantly not being able to match the performance
parameters offered by g asoline driven vehicles. Hence a driveline setup has been designed to increase the performance
parameters like gradeability and top speed of an electric moped to set it at par with the gasoline powered mopeds available
on the market. In this report we will focus on the design considerations, working principle and th e mechanism for the said
driveline as well as the design calculations and the CAD model.
Keywords automatic, centrifugal clutch, drive train, electric vehicles, freewheel, mopeds, transmission.
Electric vehicles are said to be the future of the automobile technology. T here are overwhelming advantages of electric
vehicles over gasoline vehicle s. With gasoline-electric hybr id power and all-electric power, we can achieve significant cost
and environmental savings. By adding more batteries and recharging capability to gasoline-electric h ybrid vehicles, we can
have plug-in hybrids that offer the range of hybrids (500 miles or more), plus the benefit of all-electric power for short trips,
which dramatically reduces the amount of gasoline used. EVs require no gasoline whatsoever and, when recharged from
renewable energy sources, produce zero total emissions. In fact, even if we switched from gasoline cars to EVs and plug -in
hybrids recharged by our existing utility grids (which mostly use fossil fuels), we would see a 42% national average
reduction in CO2 emissions, according to research by Peter Lilienthal of the National Renewable Energy Laboratory.
According to a study, the yearly cost o f operating 50 miles per gallon vehicle is $1275 while the same for operating an
electric vehicle is just $216. T he main issue with using a n electric vehicle, in this case an electric moped is the lack of
performance. Electric mopeds fall very short in t he performance parameters like gradeability, torque and top speed as
compared to the gasoline mopeds do minating the market today. The maximum speed possible with an electric moped is just
around 16 mph as compared to 40-50 mph top speed of their gasoline co unterparts. Hence a mechanical system has been
designed which offers both greater power and greater torque whenever the situation demands the need for the same.
5V. B. Bhandari in his book Design of Machine Elements talks about the various power transmitting components, their
application and design. The design methodology explained in the book is considered while design of mechanical components
like the two-stage gearbox, input and output sprockets, gear shafts etc. 1In the book, Electric Vehicle Technology Explained,
James Larminie and John Lowry explain the history and evolution of electric vehicles in terms of their technology and
various features that have developed over the years. The book also talks about the various components of the electric drive
system like the motor, their types and their development that i mprove vehicle characteristics such as speed, range, safety an d
reliability. 2F. K. Sully in Motor vehicle mechanic’s Textbo ok emphasizes the importance of au tomatic transmissions in
automobiles. He describes the common kinds of automatic transmission modes that are widely applied in current
automobiles. The chapter talks about their advantages and disadvantages when used in different kinds of vehicles and ways
in which they ca n be better i mplemented in the systems. 6The Motor Vehicle by T. K. Garrett, K. Newton and W. Steeds,
International Journal of Engineering Research & Science (IJOER) ISSN: [2395-6992] [Vol-3, Issue-11, November- 2017]
Page | 47
provides essential reference work for various transmission systems. It discusses in detail about the continuously variable
transmission (CVT) and its components and how the system has been developed to be practically implemented in today's
The transmission system comprises of three main components namely a single-speed two stage gearbox, a centrifugal c lutch
and freewheels.
3.1 Gearbox
An automobile requires high torque while climbing hills and while starting. On the other hand, while running on high speeds
on level roads, high torque is not required due to the vehicle momentum. The purpose of a gearbox in a vehicle is to vary the
torque on the output shaft according to the required condition. Thus, the gearbox helps to convert the high speed low torque
power generating device (engine, mo tor, etc.) to a high torque power transmitting system. In this system a single-speed two
stage gearbox is used to increase the torque on the output shaft.
The main components of a gearbox are:
3.1.1 Counter shaft
Counter shaft is the shaft that is connected with the power producing device of the system. It is coupled with power
transmitting devices like gears to transmit the power to the main shaft. The counter shaft runs with the same spee d or
different speed as that of the power producing device due to the gear ratio provided between them.
3.1.2 Main Shaft
The main shaft is t he shaft which is coupled to the output shaft or the wheel. It carries power from the counter shaft by the
use of gears according to the gear ratio and it runs at different speed and torque as compared to the counter shaft.
3.1.3 Gears
Gears are used to transmit the power from one shaft to the o ther. They are the most important components of the
transmission system as they are responsible for the variation in the torque and speed of the gearbox. This ta kes place due to
the gear ratio or reduction ratio of the gears. The gear ratio or the red uction ratio is the ratio of the dri ven gear teeth t o the
driving gear teeth. If the gear ratio is greater than one, the main shaft revolves at lower speed than the counter shaft and the
torque on the main shaft is higher than the torque on counter shaft. On the o ther hand, if the gear ratio is less than one, t he
main shaft revolves at higher speed than the counter shaft and the torque on the main shaft is lower than that on the counter
3.1.4 Bearings
Bearings are used to support the rotating shafts and reduce friction. In the gearbox the main shaft and the counter shaft are
supported by the bearings.
3.2 Centrifugal Clutch:
A clutch is a power transmitting component used to co nnect the driving shaft to the driven shaft, so that the driven shaft may
be started and stopped at will, without stopping the driving shaft. A clutch provides an interruptible connection between two
shafts. The driving shaft is connected to a boss assembly that consists of a number of shoes and springs that move radially
outwards. The driven shaft is connected to another hollow boss. When the two shafts are aligned, the boss assembly can
revolve inside the hollow boss. When the dr iving shaft is rotated, the centrifugal force due to rotation causes the shoes to
move radially outwards and come in contact with the hollow boss of the driven shaft. With enough rpm and centrifugal force,
the shoes maintain contact with the rim of the hollow boss, thus transm itting power from the driving shaft to the driven shaft.
International Journal of Engineering Research & Science (IJOER) ISSN: [2395-6992] [Vol-3, Issue-11, November- 2017]
Page | 48
The friction material used on the shoes and the inner rim of the hollow boss help in maintaining contact, while the spring
ensures ease in expansion and retraction and hence provide effective power transmission.
3.3 Freewheel Sprocket:
A freewheel is a device in a transmission system that disengages the driveshaft from the driven shaft when the driven shaft
rotates faster than the driveshaft. It uses a ratchet and pawl mechanism. It consists of two saw-toothed discs, pressing against
each other, with the toothed sides pressing. When rotating in one direction, the saw teeth of drive disc lock with the teeth of
the driven disc, making it rotate at the same speed. If the drive disc slows down o r stops rotating, the teeth of the driven disc
slip over the drive disc teeth and continue rotating. A freewheel sprocket has t his mechanism enclosed in a boss and the teeth
of a sprocket attached on the outer rim of the boss.
3.4 Sprocket:
A sprocket wheel is a power transmission device that looks like a profiled wheel with teeth or cogs that mesh with a chain,
track or other perforated or indented material. The main difference between a gear and a sprocket is that gears mesh with
each other while sprockets mesh with a chain which intern transfer po wer to other sprockets. They are useful in transmitting
power when the shafts are located at a significant distance from each other.
3.5 Drive Shaft:
A drive shaft is a mechanical component used for transmitting torque and rotation, usually used to connect other components
of a drive train that cannot b e connected directly because of the distance or the needto allow for relative movement between
them. The drive shaft is connected to the output wheels in an automobile that help in the forward locomotion of the vehicle.
Currently various modes of power transmission are implemented in vehicles. The most common modes are variab le speed
gearbox, continuously variable transmission (CVT), torque converter and h ub drive systems. These syste ms face drawbacks
such as reduced transmission efficiency, lower torque transmitting capacity, increased driver discomfort and higher costs.
The electric vehicles inherently face certain issues like lower speeds, lower vehicle range, lack of charging infrastructure and
higher costs. For the newly growing electric vehicle market, the implementation of such systems with d rawbacks will
seriously affect their impact and necessity among t he customers. Thus, it has become important to develop a transmission
system which can be effective in not only eliminating these flaws but also increase the performance of the electric vehicles.
This automatic transmission system for electric vehicles enhances the performance parameters of the electric vehicle by
increasing the torque on wheels thus providing better acceleration and gradeability as well as increasing the velocity of the