TECHNICAL FIELD
The present subject matter, in general, relates to a power propulsion system for a
hybrid two-wheeler and, in particular, relates to a power propulsion system for a hybrid two-wheeler provided with a hub motor.
BACKGROUND
Conventional motorized two wheeled vehicles are driven by an internal combustion (IC) engine. The 1C engine requires liquid or gaseous fuel for combustion. However, the amount of combustible fuel, such as crude oil, present on the earth is limited. In addition, phenomenal growth in industrialization in the last two centuries has led to depletion of combustible fuels at an alarming rate. Due to ever growing demands for fuel, the fuel cost has also gone-up exponentially over the past few years. Besides, the combustion of fuel in an internal combustion engine has also led to increased pollution all across the world. As such, it has become desirable to find alternate ways and solutions to achieve better fuel economy as well as to make the environment pollution free.
One way to achieve the aforesaid in case of vehicles may be accomplished through an electrically driven vehicle. However the battery or electrically driven vehicles suffer from a major limitation. The electrically driven vehicles are able to run over a comparatively shorter distance and thus require frequent charging of a battery installed therein, for covering long distances. This drawback has been solved with the advent of hybrid two wheeled vehicles. A hybrid two wheeled vehicle employs two power sources i.e. an electric motor and an internal combustion engine. Usually, the internal combustion engine is the main source of power while the electric motor provides supplementary or

additional power to the hybrid two wheeled vehicle. The internal combustion engine and the electric motor in the hybrid two wheeled vehicle can be used in combination with each other or can be used independently. The pollution caused by a hybrid two wheeled vehicle is significantly less as compared to the vehicles using only internal combustion engines as a power source.
However, there are inherent challenges to optimize the design of hybrid two wheeler vehicles. For example, gears are provided in two wheeler hybrid vehicles for transmitting power from the IC engine, and are directly connected to the traction wheel. However, when the vehicle is in the electrical mode of operation, the electric motor alone provides the traction force for driving the vehicle. Although the gears do not drive the traction wheel when the electrical motor is driving the traction wheel, the gears keep on rotating as they are coupled to the traction wheel. This causes a loss of power and also adds to the maintenance and servicing cost.
SUMMARY
The subject matter described herein is directed to a propulsion system of a two-wheeler.
According to at least one aspect of the subject matter described herein, the propulsion system for a hybrid two-wheeler includes a first power source, which is an internal combustion engine. The first power source is disposed transversely and substantially downwardly of the two-wheeler. A second power source, which is an electric motor, is directly coupled to a hub of at least one traction wheel of the two-wheeler. A centrifugal clutch is disposed substantially downwardly of the two-wheeler

for selectively connecting the first power source to the traction wheel of the two-wheeler thereby transmitting traction force for propelling the two-wheeler. The centrifugal clutch is disposed on a first shaft. The first shaft is freely mounted between the first drive means and the traction wheel, on a transmission case. The first power source is operably connected to the centrifugal clutch by means of a first sprocket and transmission chain assembly thereby achieving a first stage reduction. For achieving a second stage reduction, the first shaft is operably connected to the traction wheel by means of a second sprocket and transmission chain assembly thereby achieving a second stage reduction. The employment of simple sprocket and chain assemblies, for achieving desired reduction ratio, eliminates the deployment of a complex gear box.
These and other features, aspects, and advantages of the present subject matter will be better understood with reference to the following description and appended claims. This summary is provided to introduce a selection of concepts in a simplified form. This summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used to limit the scope of the claimed subject matter.
BRIEF DESCRIPTION OF THE DRAWINGS
The above and other features, aspects and advantages of the subject matter will be better understood with regard to the following description, appended claims, and accompanying drawings where:
Fig.l is a schematic elevational view of a scooter in accordance with an embodiment of the present subject matter.

Fig.2A shows a top sectional view of a fixed type propulsion system of the scooter in accordance with one embodiment of the present subject matter.
Fig.2B shows an elevationai view of the propulsion system shown in Fig.2A.
DESCRIPTION
The disclosed subject matter relates to a power propulsion system for a hybrid two-wheeler and specifically relates to a power propulsion system for a hybrid two-wheeler provided with a hub motor. The propulsion system includes two power sources which drive the hybrid two wheeler. The two power sources may be an internal combustion engine and an electric motor. Both of the mentioned power sources can either be used independently or in collaboration with each other. Also, both power sources have their respective transmission systems and motion transmitting means to transmit power to a rear wheel of the two wheeler.
According to at least one embodiment of the present subject matter, the above-mentioned propulsion system of a hybrid two-wheeler employs a fixed transmission system that incorporates motion transmitting mechanisms like sprocket chain arrangement As an example and without limiting the scope of the subject matter, the mentioned transmission system includes a two staged sprocket chain arrangement. A centrifugal clutch selectively connects the first power source to the traction wheel of the two-wheeler thereby transmitting a traction force for propelling the two-wheeler. The centrifugal clutch is disposed on a first shaft. The first power source is operably connected to the centrifugal clutch by means of first sprocket and transmission chain assembly thereby achieving first stage reduction. For achieving second stage reduction,

the first shaft is operably connected to the traction wheel by means of a second sprocket and transmission chain assembly thereby achieving second stage reduction.
The electric motor as a second power source is directly and operably connected to a hub of the rear wheel through a power transmitting means. As an example and without limiting the scope of the subject matter, the power transmitting means for transmitting power from the electric motor to the traction wheel is different from the earlier mentioned transmission system.
The propulsion system disclosed by the present subject matter does away with extra motion transmitting parts like gear box thereby being efficient in terms of net power transmitted to the traction wheel. Moreover, the disclosed propulsion system assumes a more rigid and compact shape as compared to the propulsion systems in the existing art. Further, a better maintenance and serviceability of the transmission system of the hybrid two-wheeler is achieved as the ease of changeover of defective components from the transmission system is enhanced in context of the disclosed propulsion system.
Fig.l illustrates schematic elevational view of a scooter 100 in accordance with an embodiment of the present subject matter.
For example, and by no way limiting the scope of the subject matter, the embodiments disclosed in the present subject matter are described in the context of a step through scooter having a swinging type engine and small wheels. However, the embodiments and the1 subject matter herein can also be applied to other vehicles, such as motorcycle type two or two-wheeled vehicles having rigidly mounted engines and bigger wheels, all terrain vehicles, and other step over two- wheelers.

As used herein, the terms "front", "rear", "left", "right", "up", and "down", correspond to the direction assumed by a driver of the vehicle. The scooter 100 is configured for accommodating two persons, a rider and a pillion. The scooter includes a frame 105 supporting a handlebar 110 towards a front end thereof and configured for a rotation about the steering axis. The frame 105 also supports a front wheel 115 and a rear wheel 120 on front and rear ends, respectively, thereof. The rear wheel 120 can also be addressed as traction wheel and vice versa. An internal combustion engine 125 is swingably mounted along with the transmission case 130, on the frame 105 by various mechanisms known in the existing art. An electric motor 135 is disposed on the hub of the rear wheel and forms an integral part of hub therewith. The hybrid scooter 100, thus employs two power sources i.e. the internal engine 125 and the electric motor 135.
Fig.2A shows a top sectional view of a fixed type propulsion system 200 of the scooter 100.
Fig.2B shows a elevational view of the propulsion system 200 shown in Fig.2A.
As shown in Fig.2A and Fig.2B, according to an embodiment of the present subject matter, the propulsion system 200 includes an internal combustion engine 125, an electric motor 135, a centrifugal clutch 215, and two sets of sprocket and transmission chain assembly.
A first sprocket and transmission chain assembly includes a first sprocket 225 disposed on a crankshaft 220, a second sprocket 230 coupled to the centrifugal clutch 215 and a first transmission chain 235. The first transmission chain operably connects the first sprocket 225 and the second sprocket 230 in a manner such that the rotation of first

sprocket 225 drives the second sprocket 230. The first sprocket 225 is made smaller than the second sprocket 230, to achieve desired first stage reduction ratio.
A second sprocket and transmission chain assembly includes a third sprocket 245 disposed on a first shaft 240, a fourth sprocket 250 coupled to the rear wheel 120 and a second transmission chain 255 operably connecting the third sprocket 245 and the fourth sprocket 250. The rotation of the. third sprocket 245 drives the fourth sprocket 250and vice versa. The third sprocket 245 is made smaller than the fourth sprocket 250, to achieve desired second stage reduction ratio.
The internal combustion engine 125 acts as a main power source while the motor 135 acts as a secondary power source in the hybrid scooter 100. The internal combustion engine 125 transmits power to the rear wheel 120 through a fixed transmission system disposed on one side of the hybrid scooter 100. The electric motor 135 acts as a secondary power source. The electric motor 135 transmits power directly to the rear wheel 120 through various motion transmitting means known in the existing art. The motor 135 is disposed on the other side of a frame of hybrid scooter 100, which is opposite to the side wherein transmission system is disposed.
On one side of the frame of hybrid scooter 100, a fixed transmission system extends along a transmission case 130. A first shaft 240 is freely mounted substantially on a middle portion of the transmission case 130. The transmission case 130 further supports the first sprocket and transmission chain assembly and the second sprocket transmission chain assembly. The provision of the centrifugal clutch 215 in the fixed transmission system facilitates the transmission of power from the internal combustion engine 125 to the rear wheel 120. During transmission of motion, due to the combined

effect of the two sprockets and transmission chain assemblies, a required reduction ratio is achieved and the need of a complex gear box is eliminated.
In operation, the internal combustion engine 125 rotates the crankshaft 220 which further drives the first sprocket 225 in the similar manner. The rotation of the first sprocket 225 is transmitted to the second sprocket 230 by means of the first transmission chain 235. The rotation of the second sprocket 230 is transmitted to shoes (not shown in the figure) of centrifugal clutch 215. The shoes of the centrifugal clutch 215 do not engage with the first shaft 240 till the rpm generated by the internal combustion engine 125 exceeds a certain specified speed called idling speed. Consequently, the motion from the centrifugal clutch 215 does not get further transmitted to the first shaft 240 till the idling speed is exceeded. When the rpm of the internal combustion engine 125 reaches above the aforesaid threshold, the shoes of the clutch 215 become engaged with the first shaft 240 and torque generated by the internal combustion engine 125 is finally transmitted to the first shaft 240. The rotation of the first shaft drives the third sprocket 245, which in turn drives the fourth sprocket 250 by means of the second transmission chain 255. The driven fourth sprocket 250, in turn, directly drives the rear wheel 120.
On the other side of the frame of hybrid scooter 100, the electric motor 135 acts as a secondary power source for the hybrid two-wheeler 100. In order to improve the power transmission and efficiency of the vehicle by minimizing the transmission losses, the electric motor 135 is disposed directly on the hub of the rear wheel 120 and is operably connected therewith. For example and by no way limiting the scope of the subject matter, a casing of the electric motor 135 (not shown in the figure) is rigidly attached to the hub of the rear wheel 120 through various joining means known in the

existing art. In one preferred embodiment, the casing of electric motor 135 is an integral part of the hub of rear wheel 120 acts as a motion transmitting means to transmit motion to the rear wheel 120. The electric motor 135 can be used independently or in collaboration with the internal combustion engine 125.
The electric motor 135 is supported onto the frame of hybrid two wheeled vehicle 100 by means of a support arm 260. In one embodiment, the support arm is rigidly and immovably connected to a stator (not shown in the figure) of the electric motor 135, while the motor casing (not shown in the figure) is a rotor (not shown in the figure) of the electric motor 135. In one embodiment, one end of the support arm 260 of the present subject matter may be fastened to the stator of the electric motor 135 casing through various joining means known in the existing art. The other end of the support arm 260 is attached to a crankcase 265 by various mechanisms known in the existing art.
It must be noted here that the aforementioned specifications with reference to the shape of the support arm 260 and the means for mounting the support arm 260 to the motor casing and to the crank case 265 can be easily altered to suit varying functional and technical requirements.
The motor casing, the support arm 260 and the crankcase 265 may be held together via formation of a suitable assemblage in conformity to the present subject matter. By way of example, and in no way limiting the scope of the present subject matter, the motor casing, the support arm 260 and the crankcase 265 are held together by means of fasteners, such as bolts or rivets or studs so as to form an assemblage. In another embodiment of the present subject matter, the electric motor 135 forms an integral part of the hub with an overhang wheel assembly, devoid of the support arm 260.

The present subject matter can be embodied in many other ways as would be clear to a person skilled in the art. To give example, in another embodiment, the transmission assembly can include a toothed belt to transfer motion from one sprocket to another sprocket. Similarly, in yet another embodiment, a continuously variable transmission (CVT) can be used as transmission assembly for transmitting motion from the internal combustion engine 125 to the rear wheel 120.
Further, the operation of this hybrid vehicle can be divided into three modes: In a first mode or engine mode, only 1C 125 engine acts as a power source while the electric motor 135 is idle and does not act as a power source. In a second mode, only electric motor 135 acts as a power source and provide the driving torque while IC engine is idle. In a third mode, both power sources i.e. internal combustion engine and electric motor provide driving torque to the traction wheel simultaneously.
In one embodiment the operation of the hybrid two wheeler may be further illustrated as follows. In the first mode, the internal combustion engine is in operation and rotates the crankshaft 220. The engagement of the centrifugal clutch 215 disposed on first shaft 240, facilitates the transmission of torque from the crankshaft 220 to the rear wheel 120. The electric motor 135 is idle or is in "off state. This mode may be preferably employed during highway riding conditions wherein average speed of the vehicle is high.
In the second mode or motor mode, the electric motor 135 is in operation while internal combustion engine 125 is idle. The electric motor 135 directly transmits a torque to the hub of the rear wheel 120 through various power transmitting means known in the existing art. Since the fourth sprocket 250 is rigidly coupled to the traction wheel 120, the rotation of the rear wheel 120 causes the rotation of fourth sprocket 250 which further

rotates the third sprocket 230 and first shaft 240. As the shoes of the centrifugal clutch 215 are not engaged with the first shaft 240, therefore the first shaft 240 rotates freely on its axis. The disengagement of the shoes of the centrifugal clutch 215 keeps the first sprocket and transmission chain assembly stationary. The unnecessary motion of the first sprocket and chain assembly, while only electric motor 135 is operating, is thus avoided thereby minimizing frictional losses. In one embodiment, the casing is a rotor. The second mode may be preferably employed in city riding conditions wherein average load and speed requirements are low.
In the third mode or hybrid mode, the engagement of the centrifugal clutch 215 facilitates the transmission of torque from the crankshaft 220 to the rear wheel 120. Simultaneously, the electric motor 135 is in operation and directly transmits a torque to the hub of the rear wheel 120. Thus a combined torque due to operation of both power sources rotates the rear wheel 120 at a desired traction force. This mode may be preferably employed during high torque requirement like when hybrid two-wheeler is climbing on a gradient road.
In one embodiment of the present subject matter, any one of the three modes disclosed above can be employed manually. The user/rider of the hybrid two-wheeler manually switches "on" or "off, a particular mode depending upon his requirement.
In another embodiment of the present subject matter, any one of the three modes can be employed automatically by mechanical or electronic or electromechanical actuation. Depending upon the driving conditions like high load/low load or battery charged/discharged the hybrid two wheeler switches "on" or "off, a particular mode automatically without any human intervention. In yet another embodiment of the present

subject matter, user/rider of the hybrid two-wheeler has an option to choose from manual or automatic modes as disclosed in the aforesaid embodiments.
The previously described versions of the subject matter and its equivalent thereof have many advantages, including those which are described below: Assembling the electric motor 135 at the rear wheel 120 of the hybrid two-wheeler 100 facilitates the effective power transmission and enhanced efficiency of the hybrid two-wheeler 100. This assemblage also facilitates in appropriate cooling of the electric motor 135 by enhancing the heat dissipation. Moreover, in case of servicing or maintenance, the electric motor 135 is easily accessible as it is mounted directly on the hub of the rear wheel 120.
The propulsion system disclosed by the present subject matter does away with extra motion transmitting parts like gear box thereby being efficient in terms of net power transmitted to the traction wheel 120. Moreover, the disclosed propulsion system assumes a more rigid and compact shape as compared to the propulsion systems in the existing art.
While certain features of the claimed subject matter have been illustrated and described herein, many modifications, substitutions, changes, and equivalents will now occur to those skilled in the art. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes that fall within the true spirit of the claimed subject matter.

We claim:
1. A hybrid two-wheeler vehicle (100), comprising:
a first power source (125);
a second power source (135); and
a centrifugal clutch (215);
characterized in that
said centrifugal clutch (215) is disposed on a first shaft (240), wherein the first shaft (240) is freely mounted between said first power source (125) and a traction wheel (120);
a first sprocket and a transmission chain assembly operably connects said first power source (125) to said centrifugal clutch (215) achieving a first stage reduction; and
a second sprocket and transmission chain assembly operably connects said first shaft (240) to said traction wheel (120) achieving a second stage reduction.
2. The hybrid two wheeler vehicle as claimed in claim 1, wherein said first sprocket
and transmission chain assembly comprises:
a first sprocket (225) disposed on a crankshaft (220) of said first power
source (125);
a second sprocket (230) coupled to said centrifugal clutch (215); and
a first transmission chain (235) operably connecting said first sprocket (225)
and said second sprocket (230).

3. The hybrid two wheeler vehicle as claimed in claim 1, wherein said second
sprocket and transmission chain assembly comprises:
a third sprocket (245) disposed on said first shaft (240); a fourth sprocket (250) coupled to said traction wheel (120); and a second transmission chain (255) operably connecting said third sprocket (245) and said fourth sprocket (250).
4. The hybrid two wheeler vehicle as claimed in claim 1, wherein said traction wheel (120) is a rear wheel of said hybrid two-wheeler (100).
5. The hybrid two wheeler vehicle as claimed in claim 1, wherein said first power source (125) is an internal combustion engine.
6. The hybrid two wheeler vehicle as claimed in any of the preceding claims, wherein said second power source (135) is an electric motor.
7. The hybrid two wheeler vehicle as claimed in claim 6, wherein said electric motor (135) is supported by a support arm (260) disposed between said electric motor (135) and a crankcase (265) of said internal combustion engine (125).
8. The hybrid two wheeler vehicle as claimed in claim 7, wherein a casing of said electric motor (135) is attached to a hub of said traction wheel (120).

9. The hybrid two wheeler vehicle as claimed in claim 1, wherein said casing of said
electric motor (135) is a rotor.
10. The hybrid two wheeler vehicle as claimed in claim 1, wherein said centrifugal
clutch (215), said first sprocket chain and transmission chain assembly, and said
second sprocket and transmission chain assembly are disposed on a transmission