TECHNICAL FIELD
The present subject matter, in general, relates to a power train for a hybrid two-wheeler vehicle and in particular relates to implementation of an electric motor and a fixed transmission system in a power train.
BACKGROUND
Conventionally, in two-wheeled motorized vehicles, at least one wheel is connected to and driven by an internal combustion (IC) engine. However, due to depleting crude oil reserves coupled with strict environmental norms it has become desirable to search for alternate energy sources which are abundant, cheaper, and environment friendly. Hybrid electric vehicles or hybrid vehicles were developed as one such solution to the aforesaid problem. Hybrid vehicles are fuel efficient, less noisy, and more environment friendly as compared to conventional vehicles.
In general, hybrid electric vehicles employ two power sources, i.e., an electric motor in addition to a regular liquid fuel IC engine. Usually, the electric motor employed in a hybrid vehicle is a preferred power source while the IC engine provides supplementary or, in other words, secondary power in case of battery discharge or for heavy load. The IC engine and the electric motor can be used in conjunction or independently to derive power for the hybrid vehicle.
Critical issues in the design of a hybrid vehicle mainly involve optimization of transmission system to transmit power from the IC engine or electric motor to the wheels, either independently by IC engine or electric motor or both.

Continuously varying transmission (CVT) system is one such popular transmission system used in conventional hybrid two-wheeler, which changes the transmission ratio by varying both drive pulley and driven pulley engagement diameters. For the purpose, a belt moving on the drive pulley and the driven pulley is adjusted to accommodate the change in the engagement diameters of the drive pulley and the driven pulley by either moving the belt inward or outward. However, in such an arrangement, the belt may slip over the pulleys, thus resulting in transmission losses. Also, due to beh slip, the CVT system inherently causes undesirable noise during operation. Moreover, as the CVT system is generally disposed on one side of the two-wheeler, the electric motor is placed on the other side of the two-wheeler to maintain balance and is coupled to the CVT system by a connecting means. As a result, the vehicle looks broad and bulky.
Thus, substantial belt slips during change of speeds and the aforesaid layout of the electric motor not only makes the hybrid vehicle less fuel efficient, but also affects the aesthetics of the vehicle.
Therefore there exists a challenge to design a cost effective transmission system for a hybrid two-wheeler, which is not only rigid and compact but also less noisy and more efficient in terms of power transmitted to the driven wheel.
Another challenge is to achieve a favorable lateral balance and good drivability for the hybrid two-wheeler. A further challenge is to facilitate easy conversion of a standard liquid-fuelled vehicle to a hybrid vehicle. SUMMARY
The subject matter described herein is directed to a power train for a hybrid two-wheeler, in which an electric motor and a transmission system are implemented in the hybrid two-wheeler

in such a way so as to deliver better performance and higher fuel efficiency than conventional hybrid vehicles.
For the purpose, a power train has been proposed, which mainly includes a transmission system, an IC engine, and an electric motor. Further, the transmission system includes a transmission case, which is primarily disposed along one side of the hybrid two-wheeler. The transmission case includes a first side and a second side. A driver means and a driven means are disposed on the outer surface of the first side of the transmission case. In an embodiment, the driver means is operably connected to a crankshaft of the IC engine, which is mounted on the second side of the transmission case. On the other hand, the driven means is operably connected to a shaft of the electric motor, hereinafter referred to as motor shaft, the electric motor being mounted on the first side of the transmission case. Further, the driven means can be connected to a number of other components of the hybrid two-wheeler through a gearbox. For example, the driven means may be connected to the rear wheel of the hybrid two-wheeler through the gearbox. The driver means and the driven means are operably interconnected to each other through a transmission means, for example, a belt or a chain.
Further, in accordance with an aspect of said embodiment, the driver means and the driven means may include, but are not limited to, a driver pulley and a driven pulley respectively. In yet another aspect of said embodiment, the driver means and the driven means may include, but are not limited to, a driver sprocket and a driven sprocket, respectively. The use of positive drives, such as the driven sprocket, helps in guiding the chain properly, thus avoiding chain whipping and reducing chain noise. This also eliminates transmission losses.
Further in said embodiment of the power train of the present subject matter, the electric motor can be disposed on one side of the transmission case while the IC engine can be disposed

on the other side of the transmission case. This helps in achieving a lateral balance in the hybrid two-wheeler, thereby enhancing drivability of the hybrid two-wheeler.
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 it is 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 illustrates a side view of a hybrid two-wheeler.
Fig.2A shows a perspective view of a power train of the hybrid two-wheeler, in accordance with an embodiment of the present subject matter.
Fig.2B shows a sectional top view of the power train of the hybrid two-wheeler, in accordance with the embodiment of the present subject matter.
Fig.2C shows a sectional perspective view of an electric motor mounted on a transmission case in accordance with the embodiment of the present subject matter. DETAILED DESCRIPTION
A power train of a hybrid two-wheeler primarily includes a transmission system, an electric motor connected to a motor shaft, and an IC engine. The power train may employ positive drives, such as sprocket-chain arrangement in the transmission system, thereby

minimizing transmission losses. Typically, the transmission system includes components and systems for transferring rotation from the power source to the wheels of a vehicle. In an embodiment described below, the transmission system Includes a transmission case, a gear box, the electric motor disposed on one side of the transmission case, and the IC engine disposed on the other side of the transmission case, thus simplifying the transmission system. Such a layout of the electric motor and the IC engine achieves favorable lateral balance, thereby enhancing drivability of the hybrid two-wheeler.
In an exemplary implementation, the electric motor may be mounted adjacent to a gearbox shaft without disturbing the existing arrangement in the hybrid two-wheeler. For the purpose, the electric motor may be mounted externally on the transmission case with the motor shaft coupled to the gearbox shaft through a flange. Thus, the present layout of the electric motor and the IC engine facilitates easy changeover of a standard vehicle to a hybrid vehicle. Additionally, since the use of CVT is not necessary and therefore it is possible to reduce noise.
Fig.l illustrates a side view of a hybrid two-wheeler 100. Examples of the hybrid two-wheeler 100 discussed herein are not intended to limit the scope of the subject matter, rather the subject matter can be applied to a variety of hybrid vehicles including two-wheelers and three-wheelers. The hybrid two-wheeler 100 of the present subject matter can be configured to accommodate two persons, a rider and a pillion. The hybrid two-wheeler 100 includes a seat 102, a fuel tank, a battery, a front wheel 104, a rear wheel 106, and a power train 108. The battery provides power to a variety of components of the hybrid two-wheeler 100 including the electric motor included in the power train 108. In an implementation, the power train 108 may include an IC engine, an electric motor, and a transmission system. The IC engine and the electric motor provide power to the rear wheel 106 of the hybrid two-wheeler 100 through the transmission

system. As a result, the rear wheel 106 is driven by the power received from the IC engine or the electric motor or both. Subsequently, the rear wheel 106 drives the front wheel 104 of the hybrid two-wheeler 100.
Fig.2A shows a perspective view of a power train 108 of a hybrid two-wheeler 100, according to an embodiment of the present subject matter. The power train 108 includes the transmission system, the electric motor, and the IC engine. Further, the transmission system includes a transmission case 205 having a first side I and a second side (not seen in the figure). In an implementation, the transmission case 205 may be disposed longitudinally along one side of the hybrid two-wheeler 100. The transmission case 205 is connected to a driver means 210, a driven means 215, and a transmission means 220, which are located on the first side I of the transmission case 205. The driver means 210 and the driven means 215 may be selected from a variety of choices. For example, the driver means 210 and the driven means 215 may be pulleys, which can be linked to each other through the transmission means 220, for example a belt. In another example, the driver means 210 and the driven means 215 may be sprockets linked to each other through the transmission means 220 such as a chain. In one implementation, the transmission means 220 runs around the driver means 210 and the driven means 215 to facilitate simultaneous rotation of the driver means 210 and the driven means 215.
A notional straight line 225 indicates the layout of the driver means 210 and the driven means 215 on the transmission case 205. The notional straight line 225, drawn along x-x', bisects the layout of the driver means 210 and the driven means 215 in equal halves.
In one embodiment, the driven means 215 may be directly connected to the electric motor through a motor shaft. Therefore, the driven means 215 is directly rotated by the electric motor through the motor shaft without the use of the transmission means. Whereas the IC engine is

directly coupled to the driver means 210. Based on the use of any one of the power sources or both, as discussed later, the power is transmitted from the driver means 210 to the driven means 215, or vice versa, or combined via the transmission means 220. In one of these modes, the driver means 210 and the driven means 215 is also be rotated in tandem with each other.
Fig.2B shows a sectional top view of the power train 108 of the hybrid two-wheeler 100, according to an embodiment of the present subject matter. The power train 108 of the hybrid two-wheeler 100 includes an IC engine 230 and an electric motor 235. The electric motor 235 is disposed on the first side I of the transmission case 205, while the IC engine 230 is disposed on the second side II of the transmission case 205. In an implementation, the driver means 210 is operably connected to a crankshaft 240 of the IC engine 230, thereby transferring the rotational motion of the crankshaft 240 to the driver means 210 when in operation. Similarly, the driven means 215 is directly connected to a motor shaft 245. Further, the driven means 215 may be attached to a variety of components of the hybrid two-wheeler 100 through a gearbox 250. For example, the driven means 215 can be attached to the rear wheel 106 through the gearbox 250.
The hybrid two-wheeler 100, including the power train 108, may be operated in three modes, namely, an IC engine mode, an electric motor mode, and a hybrid mode. In the IC engine mode, the IC engine 230 is switched on or in ON state, while the electric motor 235 remains idle or in OFF state. Therefore, the driven means 215 can rotate freely over the motor shaft 245 connected to the electric motor 235.
In an implementation of the IC engine mode, when a clutch 255 in the hybrid two-wheeler 100 is in an engaged position, a driving torque provided by the IC engine 230 is converted into rotational motion of the crankshaft 240 by using a variety of mechanisms already known in the art. This rotational motion of the crankshaft 240 is transferred to the driver means

210, thereby rotating the driver means 210. Further, the rotational motion of the driver means 210 is conveyed to the driven means 215 with the help of the transmission means 220. In such an arrangement, the driven means 215 rotates upon conveyance of the rotational motion from the driver means 210 to the driven means 215 through the transmission means 220.
The rotation of the driven means 215 may be further transmitted to a number of components of the hybrid two wheeler vehicle 100 through the gearbox 250. For example, the rotation of the driven means 215 is transferred to the rear wheel 106 of the hybrid two-wheeler 100 through the gearbox 250. This IC engine mode of operation is preferably employed during certain conditions such as when the average speed of the hybrid two-wheeler 100 vehicle is high or when the load on the vehicle is high.
In the electric motor mode, the electric motor 235 is operational or in ON state, while the IC engine 230 is in OFF state. Therefore, the driver means 210 rotate freely on the crankshaft 240 connected to the IC engine 230. In an implementation, the clutch 255 is in the disengaged position so that there is no transfer of the motion from the crankshaft 240 to the driver means 210 or vice-versa. In this case, the electric motor 235 provides the driving torque to the driven means 215 through the motor shaft 245, thereby rotating the driven means 215. In such a case, the transmission means 220, which is wound around the driven means 215 and the driver means 210, transfers the rotary motion of the driven means 215 to the driver means 210, which rotates freely over the crankshaft 240.
The rotary motion of the driven means 215 is transferred to a number of other components, such as the rear wheel 106 of the hybrid two-wheeler 100, through a diversity of mechanisms known in the art. This mode is preferably employed in certain conditions such as when average load and speed requirements of the hybrid two-wheeler 100 are low.

In the hybrid mode, both the IC engine 230 and the electric motor 235 are operational or, in other words, in ON state. The IC engine 230 and the electric motor 235 provide a driving torque simultaneously to the driver means 210 and the driven means 215, respectively. In an implementation, the engagement of the clutch 255 facilitates the transmission of the driving torque from the crankshaft 240 to the driver means 210, thereby rotating the driver means 210. Simultaneously, the electric motor 235 also transmits the driving torque to the driven means 215, thereby rotating the driven means 215. The rotation of the driver means 210 and that of the driven means 215 are in tandem with each other. This rotation of the driven means 215 is used for a variety of purposes as discussed above. This mode is preferably employed during a number of conditions such as when the hybrid two-wheeler 100 is climbing a hill and a high torque is required.
A user can switch between these modes, namely, the IC engine mode, the electric motor mode, and the hybrid mode, in the hybrid two wheeler vehicle 100 either manually or automatically.
In one embodiment, the driven means 215 may be connected to the motor shaft 245 such that the electric motor 235 can be mounted adjacent to the gearbox shaft 260. For the purpose, the motor shaft 245 is coupled to the gearbox shaft 260 through the flange. In this way, the electric motor 235 is on the first side I of the transmission case 205.
Fig.2C shows a sectional perspective view of the electric motor 235 mounted on the transmission case 205 according to an embodiment of the present subject matter. The electric motor 235 is disposed on the first side I of the transmission case 205 such that the motor shaft 245, the gearbox shaft 260, and the driven means 215 are coaxial. The electric motor 235 is rigidly located on the first side I of the transmission case 205 by a plurality of means. In one

implementation, two brackets 265-1 and 265-2 can be used to rigidly position the electric motor 235 on the first side I of the transmission case 205.
According to one aspect of said embodiment of the power train 108, the driver means 210, the driven means 215, and the transmission means 220 may be a driver pulley, a driven pulley and the belt respectively. Aforementioned aspect of said embodiment of the power train 108 having a pulley-belt arrangement produces significantly lower noise in operation as compared to existing solutions such as a power train subsuming a continuously varying transmission (CVT) system. Also, transmission losses due to belt slip, in the above discussed aspect of the power train 108, are also substantially minimized as compared to the CVT system.
According to another aspect of said embodiment of the power train 108, the first driver means 210, the driven means 215, and the transmission means 220 are driver sprocket, a driven sprocket, and the chain, respectively. These positive drives, such as the driver sprocket and the driven sprocket, prevent transmission losses due to slipping of the chain. The positive drives are meshed with each other and assure no slip of the transmission means 220 from the driver means 210 and the driven means 215.
From the design and implementation standpoint, the aforementioned selection vis-a-vis the assemblage and specifications thereof, aggregate number of parts therein, the total number of parts for the assemblage of the power train 108 suggested herein are merely illustrative of the present subject matter and in no way limit the scope of the present subject matter. Therefore, applicant(s) intends to encompass within the language of any structure presently existing or developed in future that performs the same function. Various modifications to the aforementioned embodiment may be readily known to persons of ordinary skill in the art having the benefit of the present subject matter. Further, the previously described versions of the subject

matter and its equivalent thereof have many advantages, including those which are described herein.
Since the electric motor 235 is located adjacent to the gearbox 250, the motor shaft 245, having the driven means 215 mounted on it, can be coupled to the gearbox shaft 260 through the flange. This facilitates easy conversion from a standard two-wheeler to a hybrid two-wheeler 100.
The subject matter described herein is not limited to a hybrid two-wheeler 100. Rather, the subject matter described herein may be applied to any two-wheeler and, more particularly, to vehicles having small wheels such as scooters.
Ahhough the subject matter has been described with reference to specific embodiments, this description is not meant to be construed in a limiting sense. Various modifications of the disclosed embodiments, as well as alternate embodiments of the subject matter, will become apparent to persons skilled in the art upon reference to the description of the subject matter. It is therefore contemplated that such modifications can be made without departing from the spirit or scope of the present subject matter as defined.

We claim:
1. A power train (108) for a hybrid vehicle, the power train (108) comprising:
a transmission system including a gearbox (250); and
an electric motor (235) coupled to a motor shaft (245);
characterized in that the electric motor (235) is externally mounted on to the transmission system and is directly coupled to the gearbox (250).
2. The power train (108) as claimed in claim 1, wherein the electric motor (235) is coupled to the gearbox (250) through a flange.
3. The power train (108) as claimed in claim 1, wherein the transmission system is coupled to an IC engine (230) through a crankshaft (240).
4. The power train (108) as claimed in claim 3, wherein the IC engine (230) and the electric motor (235) are located on opposite sides of the transmission system.
5. The power train (108) as claimed in claim 1, wherein the transmission system includes a transmission means (220), a transmission case (205), a driver means (210), and a driven means (215).
6. The power train (108) as claimed in claim 5, wherein the electric motor (235) is directly mounted on the driven means (215).
7. fhe power train (108) as claimed in claim 5, wherein the driver means (210) and the driven means (215) are pulleys.
8. The power train (108) as claimed in claim 5, wherein the driver means (210) and the driven means (215) are sprockets.
9. The power train (108) as claimed in claim 5, wherein the transmission means (220) is a belt.

10. The power train (108) as claimed in claim 5, wherein the transmission means (220) is a chaim.