DESC:Field of the Invention
[001] This invention relates to electric vehicles and more particularly to packaging of
one or more batteries within electric vehicles, particularly 2 wheeler (2W) vehicles.
Background to the Invention
[002] A strong trend to electric vehicle manufacture and use is now becoming evident
as concerns with climate change and availability of fossil fuels become evident. Electric
vehicles include a number of batteries including a large number of electric cells as a
power source and a transmission system as used in conventional vehicles. The number
of batteries and transmission system is driven largely by the required vehicle range. At
the present time, transmission system along with readily available batteries remain
bulky and this may limit their use particularly where desired vehicle range conflicts with
small vehicle size.
[003] For example, small vehicles which currently operate using liquid and gaseous
hydrocarbon fuels could advantageously be shifted to electric motor prime movers to
reduce emissions. An initial trend to reduced emission prime movers has involved
transition from petrol operated engines to gaseous fuelled engines, for example of the
LPG or CNG type. This has reduced emissions. However, proposed changes in
regulations, for example in India, is driving a shift to electrically powered vehicles and
there are obvious difficulties in reconfiguring a vehicle fleet to operate with electric
motors. Vehicle re-design and re-configuration of manufacturing plants for electric
vehicle manufacture is a potentially time consuming and costly exercise. Yet it is
desirable to meet directives/focus set by the Government of various countries.
[004] Two wheeled vehicles will also be provided with electric power in coming years.
Packaging of the electric battery and transmission is important and the present
applicant has disclosed a frame arrangement for this purpose in co-pending Indian
Patent Application No. 201821047188 filed on 13th December’ 2018, the contents of
which are hereby incorporated herein by reference.
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[005] Such vehicles must be provided with an electric motor as a prime mover and
transmission. The motor is supplied with power from batteries to produce a motive force
which is further transferred to driving wheels of the vehicle through transmission
system. The electric motor and transmission requires considerable space. Packaging
the same in given limited space is a challenge as well as a packaging arrangement shall
allow efficient transmission of electric power as torque to the driven wheel. At the same
time, the transmission must be integrated into the vehicle in a cost effective way with
minimum changes in existing vehicle layout. Aesthetic of the vehicle is an important
aspect while packaging and designing the vehicle. Hence, the packaging of the
components needs to be compact and overall aesthetics of the vehicle should not be
hampered. This may present some challenge in the case of two wheelers where space
for packaging the transmission is substantially constrained.
[006] In electric vehicles the preferred location of the battery is central lower position of
the vehicle as a battery being heavier component, central lower position helps in
providing better balance and handling of the vehicle. However; due to the central lower
position of the battery the overall longitudinal length of the vehicle may increase.
Therefore, to place the battery at desired location with minimum impact on overall size
of the vehicle is challenging.
[007] It is an object of the present invention to provide an electric vehicle design with a
compact packaging of prime mover and transmission assembly which is cost effective
and efficient.
Summary of the Invention
[008] With this object in view, the present invention provides an electric vehicle
comprising:
a frame;
an electric battery module comprising at least one battery connected to the frame;
an electric motor receiving power from the battery module;
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a transmission system provided with a transmission casing; said electric motor 20 is
closely coupled to the transmission system (80) and is mounted on the transmission
casing; and
a rear wheel receiving power from the electric motor through the transmission system
and is connected to the frame using a rear suspension system; wherein the rear wheel
is connected to the frame using said casing forming a part of the rear suspension
system.
[009] The transmission system and said electric motor are closely coupled and
mounted within the dimensions of rear wheel. This helps in compact packaging thereby
maintaining appropriate vehicle length as well as provides good aesthetics. The
transmission system may form a structural element of a suspension system and, in this
case, a number of options are available. According to first embodiment, where the
vehicle is a 2 wheeler vehicle such as a scooter, a swing arm is typically included as a
key component of the rear suspension system as it connects the rear wheel pivotably
with the frame of the vehicle. The swing arm locates the rear axle while pivoting
vertically, to allow the rear suspension system to absorb shocks from bumps in the
road. Motor may be mounted on the transmission casing. In such case, the transmission
casing (which also acts as a motor shaft casing) may act as the swing arm. One end of
the transmission casing may conveniently be mounted to the frame at a first pivot joint
forward of the rear wheel while the other end is mounted to a rear suspension member,
such as a rear shock absorber, at a second pivot joint while the transmission system is
also driveably connected to the rear wheel. Preferably, the second pivot joint is provided
on the casing itself which helps in securely mounting one end of the shock absorber
which is located on the same side of the vehicle due to the load imposed by the electric
motor and transmission systems. This option avoids any requirement for providing
separate and specialised suspension mounting arrangements thereby helping to reduce
complexity and cost. This option may also remove the need for a separate swing arm,
therefore saving cost. It also helps in compact arrangement and better aesthetics. As
the separate swing arm is not provided, weight of the vehicle is also reduced which is
one of the important aspect while designing electric vehicle.
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[010] According to second embodiment, and in an option that may include the first, the
transmission casing may not acts as a support member for the rear suspension system.
The mounting point of shock absorber is provided separately and not on the
transmission casing which may be on either side of vehicle.
[011] The vehicle may be conveniently provided with a mono-suspension with only one
rear shock absorber used to provide necessary suspension for the vehicle. Managing
the suspension with only one rear shock absorber helps in reducing the overall cost.
[012] The transmission system may be a single speed, multi stage transmission. The
number of reduction stages in the transmission system may vary based on vehicle
requirements. Preferably, a fixed ratio double stage, single speed transmission is used.
The transmission system is closely coupled with electric motor such that an output shaft
of motor is proximate to the input shaft of transmission unit and connected to transfer
the torque generated by the motor. The number of reduction stages corresponds to a
number of gear pairs. An output shaft of the motor is connected to the input shaft of
transmission through a first gear pair. The input shaft of the transmission is connected
to an output shaft through a second gear pair. Output torque received from the
transmission system is then transmitted to the rear wheel of the vehicle as the output
shaft of transmission assembly is directly connected to the axle of the rear wheel.
Alternatively, a suitable drive, such as a belt drive, may be used to transmit the power
from motor to wheel. If a separate swing arm is provided, which should not be
necessary for reasons given above, the motor and transmission assembly should be
mounted on the vehicle swing arm.
[013] The input shaft is supported at both ends by bearings, which in turn are
supported in transmission housing. The primary input gear is rotatably mounted on the
input shaft (integral in this case). The motor output shaft is connected to input shaft
coaxially by means of first gear pair, the arrangement is made such that the motor shaft
and input shaft connection lies within the input shaft length supported by the
aforementioned bearings. This helps with reducing the mesh-misalignment of the
primary gear pair, which further helps in considerable reduction in the gearbox whine
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noise. This arrangement is particularly preferable as the primary gear pair is highly
susceptible to unacceptable levels of gear whine noise due to high RPMs.
[014] According to one of the embodiment, the motor and transmission housing are
separate. The motor output shaft coming out of motor housing is connected to the
transmission housing such that the motor output shaft is supported at four locations, two
locations are within motor housing and other two locations are in transmission housing.
However; according to another embodiment, the motor & transmission housing are
integrated into a single housing wherein; the motor output shaft may be supported only
at three locations using bearings. Two locations being ends of the shaft and third
location is at a common point where two housings are integrated.
[015] The motor output shaft is provided with an input gear as an integral part of the
motor output shaft. The input gear is meshed with the teeth provided on the outer
periphery of the motor output shaft. Due to the backlash provided between the input
gear and the teeth of motor output shaft a noise is produced especially due to sudden
acceleration or deceleration at low speed level. In order to obviate this noise a silent
bush is introduced. The input gear is fitted and fixed on the motor output shaft with a
help of a bolt meshed with the internal threads provided on the inner part of the motor
output shaft. The bush is mounted in gap created between bolt and inner surface of
input gear. The bush helps in absorbing the noise thereby eliminating the problem of
noise.
[016] This layout also helps with reducing the overall width of the gearbox as most/all
of the protruding motor output shaft length is accommodated in the input shaft length.
The exceptionally low misalignment values also help in reducing the gearbox size as
other solutions for reducing whine noise might not be needed here.
[017] Further, this transmission arrangement eliminates the need of a flexible drive
transmitting element (such as chain or belt drive) to accommodate the rear wheel travel.
This results in improved driveline efficiency, better NVH characteristics and reduced
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overall servicing/adjustment requirements. Though, the flexible drive may be used if
required.
[018] The motor and transmission can be placed on either side of the vehicle. The
selected side will depend on constraints such as location of passenger foot rest, side
stand etc. A cover is desirably mounted over the transmission casing to direct air flow
towards the motor. Such cover is typically designed to improve vehicle aesthetics.
[019] The electric battery module is a relatively heavy vehicle component. For a two
wheeled vehicle, a substantially equal weight distribution along the length of the vehicle
is highly desirable to enable a driver to balance weight distribution in order to balance
the vehicle during driving. An uneven weight distribution within the vehicle, though
possible, makes it difficult for a driver to maintain vehicle balance which can ultimately
lead to unsafe conditions. Ideally, the battery or battery module is located centrally
along the width of the vehicle, preferably at a central location along the length of the
vehicle. The position of the battery plays an important role in defining the centre of
gravity (CG) of the vehicle. Desirably, the battery is positioned on a central lower side of
vehicle, shifting the CG of vehicle to substantially the same location. Such CG location
helps in improving driving stability, handling and overall efficiency of the vehicle.
[020] With the use of transmission casing as a swing arm the battery position can be
lowered. Motor and transmission system are closely coupled on the transmission
casing. This helps in a compact arrangement of batteries without increasing overall
length of the vehicle.
[021] The vehicle, as described above, is conveniently a two wheeler vehicle such as a
motorcycle or scooter.
Brief Description of Drawings
[022] The electric vehicle of the present invention may be more fully understood from
the following description of preferred embodiments thereof, made with reference to the
accompanying drawings in which:
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[023] Fig. 1 is a partial isometric view of an electric vehicle according to a first
embodiment of the present invention.
[024] Fig. 2 is a partial side view of the electric vehicle of Fig. 1.
[025] Fig. 3 is a first detail side view projected from Fig. 3 showing vehicle control unit,
motor transmission assembly and shock absorber in relation to the rear frame portion of
the electric vehicle of Fig. 1.
[026] Fig. 4 is a second detail side view projected from Fig. 3 showing the battery,
vehicle control unit and shock absorber.
[027] Fig. 5 is a schematic side section view of the rear portion of the electric vehicle of
Fig. 1.
[028] Fig. 6 is a partial side view of the rear portion of the electric vehicle of Fig. 1.
[029] Fig. 7(a) is a schematic partial rear left hand side view showing the motortransmission
position for the electric vehicle of Fig. 1.
[030] Fig. 7(b) is a schematic partial rear right hand side view showing the suspension
system for the electric vehicle of Fig. 1.
[031] Fig. 7(c) is a schematic partial left hand side isometric view showing the
suspension system for the electric vehicle of Fig. 1.
[032] Fig. 7(d) shows a detail from Fig. 7(c) showing the motor transmission assembly
which also forms part of the suspension system of the electric vehicle of Fig. 1.
[033] Fig. 8 is an isometric view showing the motor-transmission assembly for the
electric vehicle of Fig. 1.
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[034] Fig. 9 is a schematic layout of the transmission system included within the motortransmission
assembly of Fig. 8.
[035] Fig. 10 is a schematic view of layout of transmission system provided with
integral housing according to one of the embodiment of present invention
[036] Fig. 11a represents a schematic view of the transmission system with silent bush
according to one of the embodiment of present invention.
[037] Fig. 11b represents a detailed schematic view of the transmission system of Fig.
11a
Description of Preferred Embodiment of the Invention
[038] Referring now to Figs. 1 and 2, there is shown an electric vehicle 10 suitable for
use as a commuter vehicle and having a frame 11 having a head tube 12, a front
portion 12 and a rear frame portion 13. The electric vehicle 10 is a two wheeler scooter
including a front wheel 82 and rear wheel 84. Rear wheel 84 is provided with a rear
mudguard 84A and a swing arm suspension system described further below with a
single shock absorber 94. Scooter 10 is shown mounted on a stand 176 of conventional
form.
[039] The driver, who may sit on seat 103, steers electric vehicle 10 through handlebar
15 which includes brakes and horn 15A. The driver is protected by front panel or guard
160 and front mudguard 170 and may comfortably place feet on floor board 71.
[040] Electric vehicle 10 has an electric motor 20 and transmission system 80 are
closely coupled and forming an integrated motor-transmission assembly 208, powered
by an electric battery module 24 comprising a single battery as shown in Figs. 1 to 4.
Electric battery module 24 is positioned to the rear of the vehicle 10 above the electric
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motor 20 and transmission system 20, a position which provides a convenient position
for routing the wire harness.
[041] Electric motor 20 has a rating of 4kW to 10 kW (though this rating is dictated by
application) and is controlled by vehicle control unit (VCU) 100. Electric battery module
22 including at least one battery 24 each with 48 volt rating provides electric power to
motor 20. Electric battery module 22 is located below the seat 103 and the luggage
compartment 105, of the scooter 10 which demonstrates compactness as space
remains available even with a change from an internal combustion engine prime mover
to an electric motor prime mover. Electric battery module 22 includes a protective frame
structure 23.
[042] Battery module 22 requires to be securely connected to the rear frame portion 13
and a number of locking means, in the form of nut and bolt fasteners, are used for this
purpose.
[043] Scooter 10 includes a frame 11 as mentioned above and this frame structure,
which supports the electric battery module 24 and the motor-transmission assembly 208
along with further vehicle components. Frame 11 is described in the Applicant’s copending
Indian Patent Application, filed under application number 201821047188 dated
13th December’ 2018 and is therefore no further described here. It may be noted,
however, that the electric battery module 22 is a relatively heavy vehicle component.
For scooter 10, a substantially equal weight distribution along the length of the scooter
10 is highly desirable to enable a driver to balance weight distribution in order to
balance the scooter 10 during driving. To that end, the electric battery module 22 is
located centrally along the width of the scooter 10, at a central lower location along the
length of the scooter 10 below rear portion of the frame 13. This central lower position
of the battery module 22 relative to scooter 10 effectively defines the centre of gravity
(CG) of the scooter 10. Such CG location helps in improving driving stability, handling
and overall efficiency of the scooter 10.
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[044] Referring to Figs. 3 to 7(d), scooter 10 is provided with a rear mono-suspension
i.e. only one shock absorber 94 on the motor-transmission system 20/80 side of scooter
10 as most load is on this side. Shock absorber 94 is desirably of the SNS type as
described in Indian Patent No. 695/MUM/2005, is used to provide rear suspension to
reduce cost. Shock absorber 94 is located at the rear of scooter 10 rather than at its
centre.
[045] The motor 20 and transmission 80 are closely coupled and mounted within
dimensions of the rear wheel 84 as specifically shown in Fig. 7(a). This helps in a
compact packaging without hampering the overall length of the vehicle and also
provides good aesthetic. The motor-transmission casing 208B forms a structural
element of the rear suspension system. Motor-transmission casing 208B acts as a
swing arm since it is pivotally mounted both to a mounting bracket portion 133,
connecting with a tube 16 of frame 11, at pivot joint 198 forward of the rear wheel 84
and to shock absorber 94 at a pivot joint 209. The shock absorber has a fixed mounting
to mounting bracket 194 connected to a rear tube 13C of the rear frame portion 13.
Such mounting allows the motor-transmission assembly 208 to vertically pivot in the
manner of a swing arm. As scooter 10 moves along a road, the shock absorber 94
spring element is variably placed into tension and compression, the motor-transmission
casing 208B correspondingly pivoting as a swing arm absorbing shocks from bumps in
the road. The cost and weight of a dedicated swing arm is thereby avoided.
[046] The mounting arrangements described above also allow the transmission casing
208B to act as a support member for the rear suspension system. The further pivot joint
209 is provided on the casing 208B itself which helps in securely mounting one end of
the shock absorber 94. This option avoids any requirement for providing separate and
specialised suspension mounting arrangements thereby helping to reduce complexity
and cost.
[047] Further features of the transmission system 80 which transmits torque from
electric motor 20 under the supervision of vehicle control unit 100 are now described
with reference to Fig. 9. The transmission system 80 is a single speed or single
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reduction type transmission. The number of reduction stages in the transmission system
80 may vary based on vehicle requirements. A fixed ratio double stage transmission
system 80 with a single pair of input and output gears is used. The motor 20 is closely
coupled with the transmission system such that an output shaft 120 of motor 20 is
proximate to the input shaft of transmission system 80 and connected to transfer the
torque generated by the motor 20. The number of reduction stages corresponds to a
number of gear pairs. The output shaft 120 of the motor 20 is connected to the input
shaft 801 of transmission system through a first gear pair 301, 302. According to one of
the embodiment, the output shaft 120 of the motor is supported at four locations i.e. at
both the ends (910 & 940) one end being in motor housing 20A while other end is
supported at transmission housing 80A. The output shaft 120 is also supported at
middle section using bearings provided at motor housing 20A and transmission housing
80A. The input shaft is supported at both ends by bearings, which in turn are supported
in transmission housing 80A. The primary input gear 302 is rotatably mounted on the
input shaft 801 (integral in this case). The motor output shaft 120 is connected to input
shaft coaxially by means of internal splines 120A, the arrangement is made such that
the motor shaft 120 and input shaft 801 connection lies within the input shaft length
supported by the aforementioned bearings. The input shaft 801 of the transmission
system is connected to the output shaft 802 of transmission system 80 through a
second gear pair 401, 402. Output torque received from the transmission system 80 is
then transmitted to the rear wheel 84 of the scooter as the output shaft 802 of
transmission system 80 is directly connected to the axle of the rear wheel 84. A suitable
drive, such as a belt drive, may be used to transmit the power from motor to wheel.
[048] According to another embodiment of present invention, the transmission system
is further improved as shown in Fig. 10. Instead of separately providing motor housing
20A and transmission housing 80A, both the housings are integrated into a single
housing 2080. This eliminates the various problems such as noise, difficulty in
assembling two different housings with mounting of motor output shaft 120 etc. The
motor output shaft 120 is supported at three locations (910, 940 & 1000) instead of four
locations, this helps in reducing noise as well as helps in easy assembly. The shaft 120
is supported only at a common single location (1000) in middle location whether both
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the housings (20A & 80A) are integrated. Both the ends of the motor output shaft 120
are supported at housing 2080 using bearings (910 & 940) as in previous embodiment.
One bearing pair is therefore eliminated thereby reducing complexity & cost.
[049] The motor output shaft 120 is provided with an input gear 301 as an integral part
of the motor output shaft 120. The motor output shaft 120 is provided with teeth on its
outer periphery to mesh with an input gear 301 of first gear pair. Due to the backlash
provided between the internal teeth of input gear 301 and the teeth of motor output shaft
120 a noise is produced especially due to sudden acceleration or deceleration at low
speed level. In order to obviate this noise a silent bush 177 is introduced as illustrated in
Fig. 11a and 11b. The input gear 301 is fitted and fixed on the motor output shaft 130
with a help of a bolt 137 meshed with the internal threads provided on the inner part of
the motor output shaft 120. The bush 177 is mounted in gap created between bolt 137
and inner surface of input gear 301. The bush 177 helps in eliminating the problem by
absorbing the noise.
[050] A cover 208A is desirably mounted over the transmission casing 208B to direct
air flow towards the motor 20. Such cover 208A, shown schematically in Fig. 7d is
typically designed to improve vehicle aesthetics.
[051] Modifications and variations to the electric vehicle described in the present
specification may be apparent to skilled readers of this disclosure. Such modifications
and variations are deemed within the scope of the present invention. ,CLAIMS:We Claim:
1. An electric vehicle 10 comprising:
a frame 11;
an electric battery module 24 comprising at least one battery connected
to the frame;
an electric motor 20 receiving power from the battery module 24;
a transmission system 80 provided with a transmission casing 208B;
said electric motor 20 is closely coupled to the transmission system (80) and is
mounted on the transmission casing (208B); and
a rear wheel 84 receiving power from the electric motor 20 through the
transmission system 80 and said rear wheel 84 is connected to the frame using
a rear suspension system; wherein the rear wheel 84 is connected to the frame
11 using said casing 208B forming a part of the rear suspension system.
2. An electric vehicle 10 as claimed in claim 1 wherein; the transmission system
(80) and said electric motor (20) are closely coupled such that said transmission
system (80) and said electric motor (20) are mounted within the dimensions of
rear wheel (84).
3. An electric vehicle 10 as claimed in any of the claim above wherein; the
transmission system 80 is a single speed, multi stage transmission wherein; the
transmission system 80 and said electric motor (20) are closely coupled such
that an input shaft 801 of transmission system 80 is connected to an output
shaft of the motor 20 through a first gear pair and the input shaft 801 of the
transmission is further connected to an output shaft 802 of transmission system
80 through a second gear pair wherein; the output shaft 802 of the transmission
system 80 is connected to the rear wheel 84 of the vehicle 10 for transmitting
the torque.
4. An electric vehicle 10 as claimed in claim 1 wherein; the casing 208B of the
transmission system 80 forms a structural element of a suspension system of
the vehicle 10 in a form of a swing arm used to connect the rear wheel 84
pivotably with the frame of the vehicle 10.
5. An electric vehicle 10 as claimed in claim 4 wherein; the swing arm is
connected to the frame 11 at a first pivot joint 198 forward of the rear wheel 84
and to the second pivot joint 209 at a rear axle of the rear wheel 84 such that
the swing arm pivots vertically, to allow the rear suspension system to absorb
shocks from bumps in the road.
6. An electric vehicle 10 as claimed in claim 4 wherein; the suspension system
comprises at least one shock absorber 209 mounted at the transmission casing
208B.
7. An electric vehicle 10 as claimed in any of the claim above wherein; the
transmission system 80 utilizes a chain or belt drive to transmit the power from
the motor 20 to wheel.
8. An electric vehicle 10 as claimed in claim 3 wherein; the input shaft 801 of
transmission system 80 is supported at both ends by bearings (910, 940) in a
transmission housing 80A and a primary input gear (302) of first gear pair is
rotatably mounted on the input shaft 801 connecting with the motor 20 output
shaft 120 such that the motor 20 output shaft 120 and the transmission input
shaft 801 connection lies within the transmission input shaft length.
9. An electric vehicle 10 as claimed in claim 3 wherein; the transmission system
80 is provided in transmission housing 80A and motor 20 is provided in a motor
housing 20A wherein; both the transmission housing 80A and motor housing
20A are separate and connected to each other such that the motor output shaft
120 is supported at four locations (910, 920, 930, 940) through bearings
wherein; two locations (910, 920) are present in motor housing 20A and two
locations (930, 940) are present in transmission housing 80A.
10. An electric vehicle 10 as claimed in claim 3 wherein; the transmission system
80 and motor 20 are provided in a common integral housing 2080 such that the
motor output shaft 120 is supported through bearings at three locations
wherein; two locations (910,940) are ends of the motor output shaft 120 and
third location 1000 is at an intermittent location of the motor output shaft 120.
11. An electric vehicle 10 as claimed in claim 3 wherein; the first gear pair
comprises an input gear 301 mounted on the motor output shaft 120 using a
bolt 137 wherein; the bolt 137 is meshed with internal threads provided on the
inner part of the motor output shaft 120 and a bush 177 is mounted in a gap
created between bolt 137 and inner surface of input gear 301.
12. An electric vehicle 10 as claimed in any of the claim above wherein; the
transmission casing 208B is provided with a cover 208A to direct airflow
towards the motor 20.
13. An electric vehicle 10 as claimed in any of the claim above wherein; the electric
battery module 24 is mounted centrally and below the rear frame portion (13B).