Single Speed Transmission for Electric Vehicles

1. VISVESVARAYA TECHNOLOGICAL UNIVERSITY
VIII Sem BE (Mechanical) Seminar Report
“Single Speed Transmission for Electric Vehicles”
By
Sameer Shah 1MV13ME123
Faculty Supervisor
Sampath Kumar
DEPARTMENT OF MECHANICAL ENGINEERING
SIR M. VISVESVSRAYA INSTITUTE OF TECHNOLOGY
Academic Year: 2016-17

2. SIR M. VISVESVSRAYA INSTITUTE OF TECHNOLOGY, BANGALORE
DEPARTMENT OF MECHANICAL ENGINEERING
CERTIFICATE
This is to certify that Mr Sameer Shah USN 1MV13ME123 a student of VIII
Semester be (Mechanical) in Department of Mechanical Engineering of Sir M.
Visvesvaraya Institute of Technology has successfully presented the seminar on
“Single Speed Transmission for Electric Vehicles“ to fulfil academic
requirement of Seminar (10ME86L)
Sampath Kumar Dr K S Shanmukharadhya
Faculty Supervisor H.O.D Mechanical
Evaluators:
Name Signature with Date
1. _______________ _________________
2. _______________ _________________

3. TABLE OF CONTENTS
1. INTRODUCTION
2. HISTORY OF TRANSMISSIONS
3. DESIGN REQUIREMENTS OF A SINGLE-SPEED TRANSMISSION
4. DESIGN OF HELICAL GEAR
5. MATERIAL SELECTION
6. STRUCTURAL SIMULATION
7. GEAR MANUFACTURING
8. GEAR FINISHING
9. LUBRICATION
10. ADVANTAGES
11.LIMITATIONS
12.CONCLUSIONS
13.REFERENCES

4. Chapter 1
INTRODUCTION
A transmission is a machine in a power transmission system, which provides controlled
application of the power. Often the term transmission refers simply to the gearbox that uses
gears and gear trains to provide speed and torque conversions from a rotating power source to
another device.
The most common use is in motor vehicles, where the transmission adapts the output of the
internal combustion engine to the drive wheels. Such engines need to operate at a relatively
high rotational speed, which is inappropriate for starting, stopping, and slower travel. The
transmission reduces the higher engine speed to the slower wheel speed, increasing torque in
the process. Transmissions are also used on pedal bicycles, fixed machines, and where
different rotational speeds and torques are adapted.
Often, a transmission has multiple gear ratios (or simply "gears") with the ability to switch
between them as speed varies. This switching may be done manually (by the operator) or
automatically. Directional (forward and reverse) control may also be provided. Single-ratio
transmissions also exist, which simply change the speed and torque (and sometimes
direction) of motor output.
Single Speed Transmissions consists of a single reduction gear, reverted gear or a compound
gear train. The function of reduction gear is to reduce the RPM of the high speed motor or
engine and thereby increasing the torque. In reverted gear train single speed transmission,
there is a compound gear train arranged in reverted order. There are 2 or more gear trains
which have same or different gear ratio depending on the application and type of vehicle.
Fig 1.1: Single Speed Transmission Fig 1.2: Layout of reverted single-speed transmission
Single Speed Transmissions are advantageous since there is no shifting of gears needed and
there is no need of clutch when compared to manual and automatic transmissions. Also the
gear ratio is fixed which can be set while designing the gearbox. It amplifies the input torque
and reduces the speed which makes it’s a best match when coupled with a high speed motor.
Several cars such as Chevrolet Bolt, Tesla Model S etc. use a single speed transmission
coupled with a powerful electric motor which reduces emissions and thereby eliminates the
use of clutch. Input torque is varied automatically and hence cars operate at high efficiencies.

5. Chapter 2
HISTORY OF TRANSMISSIONS
French inventors Louis-Rene Panhard and Emile Levassor are credited with the development
of the first modern manual transmission. They demonstrated their three-speed transmission in
1894 and the basic design is still the starting point for most contemporary manual
transmissions.
A manual transmission is a type of transmission used in motor vehicle applications. It uses a
driver-operated clutch engaged and disengaged by a foot pedal or hand lever, for regulating
torque transfer from the engine to the transmission; and a gear selector operated by hand or
by foot.
The automatic transmission, introduced in 1939, switches to the optimum gear without driver
intervention except for starting and going into reverse. The type of automatic transmission
used on current American cars usually consists of a fluid device called a torque converter and
a set of planetary gears. The torque converter transmits the engine’s power to the
transmission using hydraulic fluid to make the connection. For more efficient operation at
high speeds, a clutch plate is applied to create a direct mechanical connection between the
transmission and the engine.
A continuously variable transmission (CVT) uses a belt that connects two variable-diameter
pulleys to provide an unlimited number of ratio changes and uninterrupted power to the
wheels; CVT transmissions offer better fuel efficiency than conventional automatic
transmissions, which change the transmission ratio by shifting gears.
Single Speed Transmission
Fig 2.1 Single Speed Transmission
Through its high-efficiency geartrain and compact, low-weight design, the BorgWarner
eGearDrive transmission contributes to extended battery-powered driving range, which in
turn reduces the required amount of battery capacity needed. According to the company, this
single-speed gearbox also achieves higher torque capacity with 98% efficiency, while
providing smooth, quiet operation. First commercialized on the Tesla Roadster, the
eGearDrive has been developed for the emerging vehicle electrification market. Designed for
fast-to-market implementation, annual volumes are expected to increase rapidly over the next
few years.

6. Chapter 3
DESIGN REQUIREMENTS OF A SINGLE-SPEED TRANSMISSION
Transmissions should be able to
 Deliver high torque output.
 Should have minimum transmission losses
 Should overcome the effect of driving resistance caused by wheel resistance FR, air
resistance FL, gradient resistance FST and acceleration resistance FA.
 Should have minimum wear.
 Should operate smoothly and should have a cooling and lubricating system.
Case Study
If a Single Speed transmission is to be designed for electric cars with an electric motor which
has a power rating of 65 kW, output torque of 100 Nm and speed of 12000 RPM.
These inputs of the motor have to be amplified to 1000 Nm before it is delivered to the
wheels considering all the inefficiencies and losses. So a Single speed transmission should
have a gear ratio of approx. 10:1 and should be made of helical gears to reduce noise and
backlash which is more prominent in spur gears.
Vehicle Conditions for case study
 Outside temp 43 deg C
 AC ON
 19 INCH Wheel dia
 Speed 80 kmph
 Battery weight 500 kgs
 Passenger + luggage = 300 kgs
 Kerb Weight = 2000 kgs
 Total Weight = 2300 kgs
Fig 3.1 Free body diagram of a car at incline plane
According to free body diagram, (let us assume coefficient of friction μ=0.7 and ϴ = 20.299)
Maximum reaction force on an incline F = mg sinϴ + μmg sinϴ
F = (2000 * 9.81* 0.346935) + (0.7 * 2000 * 9.81 * 0.9378)
F = 6806.86 + 12878.95 = 19687.81 N
We know that torque τ = Fr (assuming r = 0.019 m for 15 inch tyre)
τ = 19687.81 * 0.019 = 375.02 N
τ = 750 N (considering FOS = 2)
this force will act on the opposite end of the gear thereby a strong design is required.

7. Chapter 4
DESIGN OF HELICAL GEAR
For the above conditions, a helical gear was designed by putting all the formulas in MS-Excel
to perform iterations and carry out calculations based on Lewis Procedure and AGMA
(American Gear Manufacturer’s Association) Formulas.
Fig 4.1 Screenshot from the Excel Sheet of Calculations
FORMULAS USED

8. Chapter 5
MATERIAL SELECTION
According to the requirements, 18CrNiMo7-6 was chosen which has Yield strength of 785
MPa and Ultimate Strength of 1100 MPa.
Fig 5.1 Material properties of 18CrNiMo7-6

9. AGMA FORMULAS

10. Based on the above calculations and iterations, a gear ratio of 3.5:1 was found to be most
suitable for the application since if 2 sets of 3.5:1 gears are in compound configuration, the
gear ratios would multiply and hence the net gear ratio would be
3.5 x 3.5 = 12.25:1
Considering certain inefficiencies in power transmission such as
 Power lost due to friction
 Power loss due to backlash error
 Power loss due to mechanical linkages between the transmission and wheel
So, acc to gear ratio of 12.25:1
= Gear ratio ………….. = 12.25
τ output = 12.25 * 100 = 1225 Nm
Let us assume these inefficiencies corresponds to 0.85 times the input
The net estimated torque which would come out of the wheels after considering inefficiencies
would be
Actual Torque = 0.85 * 1225 = 1041.25 Nm
Now this is the theoretical torque output. Structural Simulation has been showed for a
particular gear design which can withstand the input torque and reaction torque under
boundary conditions. Also the actual torque would vary when the system would be made and
installed on the vehicle. This can be recorded on dynamometer tests which would measure
the break horse power and thereby calculated torque by
τ =

11. Chapter 6
STRUCTURAL SIMULATION
Structural simulation of the gears were carried out on ANSYS 17.1 under the following
conditions
Material 18CrNiMo7-6
Yield Strength 785 MPa
Ultimate Strength 1100 MPa
Mesh = Fine
Frictionless support at the center
Moment on Pinion = 250 Nm
Reaction Moment on Gear = 708 Nm
Fig 6.1 Deflection in Gear
Maximum Deflection = 0.01806 mm
Fig 6.2 Strain in gear element

13. Chapter 7
GEAR MANUFACTURING
Materials used to produce gears may include steel-which is the most common material, and
various nonferrous materials including plastics and composites. Manufacturing methods
include: machining, forging, casting, stamping, powder-metallurgy techniques, and plastic
injection moulding. Of these, machining is the most common manufacturing method used.
Gear machining is classified into two categories:
• Gear Generating
• Gear Form-Cutting
Gear generating involves gear cutting through the relative motion of a rotating cutting tool
and the generating, or rotational, motion of the workpiece. The two primary generating
processes are hobbing and shaping.
Hobbing uses a helically fluted cutting tool called a hob. Both the hob and the workpiece
rotate as the hob is fed axially across the gear blank. Hobbing is limited to producing external
gear teeth on spur and helical gears. Hobbing can be performed on a single gear blank, but
also allows for stacking of multiple workpieces, increasing production rates.
Shaping produces gears by rotating the workpiece in contact with a reciprocating cutting tool.
The cutter may be pinion shaped, a multi-tooth rack-shaped cutter, or a single-point cutting
tool. Gear form-cutting uses formed cutting tools that have the actual shape, or profile,
desired in the finished gear. The two primary form-cutting methods are broaching and
milling.
Broaching is the fastest method of machining gears and is performed using a multi-tooth
cutting tool called a broach. Each tooth on the broach is generally higher than the preceding
tooth. As a result, the depth of cut increases with each tooth as the broaching operation
progresses. Broaching is typically used to produce internal gear teeth. External teeth can be
broached using “pot broaching”. In this process a hollow broaching tool, called the pot, is
used to cut the gear teeth.
Milling is a basic machining process which uses the relative motion between a rotating,
multi-edge cutter and a workpiece to cut individual gear teeth. A variation of the process,
called “gashing”, is used to produce large, coarse-pitch gears. Gashing is used on heavy-duty
milling machines and involves plunging the rotating cutter into a blank for rapid metal
removal.

14. Chapter 8
GEAR FINISHING
After manufacturing, gears require a number of finishing operations. Finishing operations
include heat treatment and final dimensional and surface finishing. This finishing can be
accomplished using:
• Shaving
• Grinding
• Honing
Shaving is performed with a cutter having the exact shape of the finished gear tooth. Only
small amounts of material are removed by a rolling and reciprocating action. The process is
fast but generally expensive due to the cost of machinery and tooling. Shaving is typically
performed prior to heat treating.
Grinding sometimes serves as an initial gear production process, but is most often employed
for gear finishing. Grinding is classified as either form grinding or involute-generation
grinding.
Form grinding uses wheels having the exact shape of the tooth spacing. The grinding wheels
are either vitrified-bond wheels, which require periodic re-dressing, or Cubic Boron Nitride
(CBN) wheels, which can last hundreds of times longer than vitrified wheels without
dressing.
Involute-generation grinding refers to a grinding wheel or wheels used to finish the gear tooth
by axially rotating the workpiece while it is reciprocated in an angular direction, which in
turn is determined by the type of gear being finished. This type of grinding is performed
either intermittently or continuously. Intermittent grinding uses tooth profiles dressed on cup
wheels, or on one or two single-rib wheels. Each tooth is ground individually, then the next is
indexed to the wheel. Continuous grinding uses grinding wheels with the rack profile dressed
helically on the outside diameter. Both the grinding wheel and the work turn in timed
relationship for continuous finishing.
Honing involves the meshing of the gear teeth in a cross axis relationship with a plastic,
abrasive impregnated gear shaped tool. The tool traverses the tooth surface in a back and
forth movement parallel to the workpiece axis. Honing polishes the gear tooth surface and
can be used to correct minor errors in gear tooth geometry.

15. Chapter 9
LUBRICATION
Lubrication is the process or technique employed to reduce friction between, and wear of one
or both, surfaces in proximity and moving relative to each other, by interposing a substance
called a lubricant in between them. The lubricant can be a solid, a solid/liquid dispersion, a
liquid such as oil or water, a liquid-liquid dispersion (a grease) or a gas. With fluid lubricants
the applied load is either carried by pressure generated within the liquid due to the frictional
viscous resistance to motion of the lubricating fluid between the surfaces, or by the liquid
being pumped under pressure between the surfaces. The science of friction, lubrication and
wear is called tribology. Adequate lubrication allows smooth continuous operation of
equipment, reduces the rate of wear, and prevents excessive stresses or seizures at bearings.
When lubrication breaks down, components can rub destructively against each other, causing
heat, local welding, destructive damage and failure.
The lubricant selected for this Transmission design is
Omega 690
OMEGA 690 SAE 75W140 is formulated with a special blend of fully synthetic base fluids
to provide outstanding low-temperature fluidity as well as superior high-temperature oil film
strength. q LOW TEMPERATURE APPLICATION: OMEGA 690 SAE 75W140 is
eminently suitable for use at ambient temperatures as low as –40°C. It gives the gear a
smooth and quiet start during cold running and yet maintains a high oil viscosity to protect
the gear metal surfaces from all forms of wear and scoring after warming up. q FUEL
ECONOMY: Because of the lower fluid drag generate during the starting period, OMEGA
690 SAE 75W/140 produces fuel savings of up to 5% when compared to monograde or
conventional multigrade gear oils. q OUTSTANDING SHEAR STABILITY: Because of the
severe shearing encountered in gear service, ordinary multigrade and extra-range multigrade
gear oils can suffer from huge viscosity loss during service. The special blend of fully
synthetic base fluids in OMEGA 690 SAE 75W140 is designed to overcome this
shortcoming. When tested according to the Volkswagen KRL test method, the viscosity drop
is less than 5% q SUPER PERFORMANCE: Like other grades of OMEGA 690, SAE
75W140 meets and exceeds the API GL-6 performance level. It protects gears from wear and
scoring in a manner far superior to that of ordinary gear oils meeting the API GL-5 standard
Fig 9.1 Omega 690 Gear Oil Properties Fig 9.2 Clinging action of oil

16. Fig 9.3 Comparison of Omega 690 with conventional gear oil
Omega 690 has material clinging properties which always maintains a film of lubricant between gears.
Fig 9.4 Demonstration of Omega 690 in case of Leak
In case of any leakages, the oil does not separates from the gears.

17. Advantages
Single Speed Transmission has the following advantages
• Direct drive
• Occupies less space
• No complex gear systems and gear changes
• Smooth operation and Instant torque when coupled to the motor
• Cheap, economical and easy to construct
• Low maintenance and losses when compared to Manual and automatic T.
Limitations
Single Speed transmission has a fixed gear ratio.
Conclusion
The above Single speed transmission has been designed for a case study and different
parameters and conditions were considered while designing. The requirements were noted
down and based on that Gear design was carried out.
Further the design was checked for strength using Lewis formulas and AGMA Standards.
Structural simulation was carried out on ANSYS under the boundary conditions and the
deflection was recorded.
Gear manufacturing processes and finishing processes were defined.
Lubricant was suggested which requires no PUMP to recirculate.

18. References
[1] M. Göckler. Transmission Actuation: Further Development of Existing Systems and New
Application Areas. Friedrichshafen: VDI-Society Product and Process Design, 2015 [2]
American Society of Heating, Refrigerating, and Air-conditioning Engineers (ASHRAE),
1983, Handbook: Equipment, Chapter 13: Steam-jet refrigeration equipment, Atlanta, GA,
USA
[2] The Automotive Transmission Book by Fischer, R., Küçükay, F., Jürgens, G., Najork, R.,
Pollak, B
[3] Automotive Transmissions Fundamentals, Selection, Design and Application by
Naunheimer, H., Bertsche, B., Ryborz, J., Novak, W
[4] https://en.wikipedia.org/wiki/Transmission_(mechanics)