FIELD OF INVENTION

[0001] The present invention generally relates to an internal combustion engine for a saddle type vehicle. More particularly, the present invention relates to an internal combustion engine comprising a transmission system and an electric motor unit for a saddle type two wheeled or three wheeled vehicle.

BACKGROUND OF INVENTION

[0002] Saddle type vehicles are powered by an internal combustion (IC) engine. However, due to depleting crude oil reserves and with strict environmental norms it has become desirable to design saddle type vehicles which can be powered by alternate sources of energy. Saddle type hybrid vehicles were developed to address above described concerns. Generally, hybrid vehicles are powered by an internal combustion engine, and an electric motor. The internal combustion engine installed on such hybrid vehicle uses fuel as any other conventional internal combustion engine. The electric motor is powered by an auxiliary power source such as a battery system located in the hybrid vehicle. The internal combustion engine and the electric motor can be used in conjunction or independently to derive power for the hybrid vehicle based on different user modes. In all hybrid vehicles, a transmission system is configured to transfer the rotary motion from the internal combustion engine and the electric motor to the wheels for driving the hybrid vehicle.

[0003] One of the major challenges involved in the design of transmission system of a hybrid vehicle such as a saddle type vehicle is to improve efficiency of the system, improve operability and reduce transmission losses. Further, the transmission system including the electric motor has to be integrated with existing layout of the IC engine which is difficult. Furthermore, it is desirable to have a hybrid saddle type vehicle like a moped or a small scooter having common requirements of low cost, high efficiency, and good controllability throughout the entire speed range. BRIEF DESCRIPTION OF DRAWINGS

[0004] The detailed description of the present subject matter is described with reference to the accompanying figures. Same numbers are used throughout the drawings to reference like features and components. [0005] Fig. 1 illustrates a side view of a two-wheeled saddle type vehicle employing an embodiment of the present subject matter.

[0006] Fig. 2a. and Fig. 2b. illustrates side view and top view respectively of the internal combustion engine with an additional gearbox according to a first embodiment of the present subject matter. [0007] Fig. 3. illustrates the cross sectional view (X-X) of the internal combustion engine and the additional gearbox according to the first embodiment of the present subject matter.

[0008] Fig. 4. illustrates an exploded view of the additional gearbox operably mounted to the internal combustion engine according to the first embodiment of the present subject matter.

[0009] Fig. 5. illustrates the cross sectional view (X-X) of the internal combustion engine and the exploded view of the additional gearbox according to the first embodiment of the present subject matter.

[00010] Fig. 6a. and Fig. 6b. illustrates side view and top view of the internal combustion engine with the additional gearbox according to the second embodiment of the present subject matter.

[00011] Fig. 7. illustrates the exploded view of the additional gearbox operably mounted to the internal combustion engine according to the second embodiment of the present subject matter. [00012] Fig. 8. illustrates the cross sectional view (X-X) of the internal combustion engine and the additional gearbox according to the second embodiment of the present subject matter.

[00013] Fig.9. illustrates a cross sectional view (X-X) of the internal combustion engine and the exploded view of the additional gearbox according to the second embodiment of the present subject matter.

DETAILED DESCRIPTION

[00014] Various features and embodiments of the present invention here will be discernible from the following further description thereof, set out hereunder. In the ensuing exemplary embodiments, the vehicle is a saddle type two wheeled vehicle with a step-through frame colloquially called moped. However it is contemplated that the disclosure in the present invention may be applied to any saddle type two wheeled vehicle or three wheeled vehicle. The detailed explanation of the constitution of parts other than the present invention which constitutes an essential part has been omitted at suitable places.

[00015] Generally, a two-wheeled or three wheeled vehicle can either be a straddle type vehicle wherein the rider sits straddling the vehicle, or a step-through type vehicle having a floorboard wherein the rider can place his feet besides some luggage. In both the straddle and step-through type vehicles, an IC engine is disposed in front of a rear wheel axle of the vehicle and is supported by a frame assembly. Typically, while the frame assembly acts as a skeleton for the vehicle that supports the vehicle loads, the IC engine is functionally connected to a rear wheel of the vehicle by some end transmission means such as a sprocket and chain drive for providing torque multiplication between the engine and the rear wheel and thereby provides forward motion to the vehicle. Such saddle type vehicles have common requirements of low cost, high efficiency, good controllability throughout the entire speed range. They can either have single speed transmission system or multi-speed transmission system. [00016] Small sized step through type saddle type vehicles of 100 cubic capacity or less have a single-speed transmission. In such vehicles there is a disadvantage of low torque at low speeds and speed limitations during high torque conditions. For example, when the saddle type vehicle is climbing a gradient on the road or if it has to pull a heavy load there is requirement of a high torque at the rear wheel to pull the vehicle, and the engine may not be able to provide the same. Further, moving at low speeds with less torque results in loss of fuel economy. Furthermore, at higher speeds, a fixed transmission ratio gives limitation to speed at which the vehicle can travel and resulting in loss of fuel economy. Hence, the engine may not be able to provide sufficient torque and the internal combustion engine may get switched off. All these drawbacks contribute to lowering of the fuel economy. Hybrid saddle type two wheeled vehicles serve to address the drawbacks of engine powered saddle type vehicles as discussed in previous paragraphs.

[00017] Typically, in hybrid vehicles the IC engine and the electric motor can be configured in uniquely different ways, but essentially can be classified according to the type powertrain system it has, which determines how the internal combustion engine and the electric motor interact with each other. There are two types namely, series configuration and parallel configuration. In series configuration, a battery system is charged by the internal combustion engine, which in turn powers the electric motor to drive the hybrid vehicle. In parallel configuration, the internal combustion engine and the electric motor work in together to generate the power that drives the hybrid vehicle. Both configurations are usually used and can be designed to enable the internal combustion engine and electric motor to provide power independently or in conjunction with one another with different modes of operation. [00018] Further, in hybrid vehicles a traction motor is integrated within and housed in a crankcase of the IC engine. This involves extensive modification in engine layout which is undesirable. Alternatively, the traction motor may be mounted externally on the hub of the rear wheel with the drive from the traction motor directly connecting the rear wheel. The traction motor is heavy and the hub requires extensive modifications to receive the drive both from the IC engine, and the traction motor and to accommodate the rear braking systems. Since, the drive of the traction motor is directly connected to the rear wheel, the rotary output of the traction motor does not get any benefit or ratio advantage of any gearing system and end transmission means to multiply the torque output. This necessitates the use of a large powered traction motor drawing large power from the battery. This reduces the life of the battery and also reduces the vehicle range that it can operate.

[00019] Other critical issues involved in the design of hybrid powertrain and transmission system include improving efficiency, improving operability and to reduce transmission losses of the system while retaining attractive features such as low cost and easy drivability.

[00020] The present subject matter seeks to provide a hybrid system for a saddle type vehicle by introduction of a traction motor operated by a battery connected thereto and working in parallel with the IC engine. The IC engine and traction motor have parallel power flow to the rear wheel.

[00021] The present subject matter additionally seeks to provide a hybrid system which can be implemented involving least modifications to the existing layout of the IC engine and the vehicle layout while retaining many key transmission components.

[00022] The present subject matter additionally seeks to provide a retrofitable traction motor that can easily be attached and detached from the saddle type vehicle when the hybrid system is not required.

[00023] The present subject matter additionally seeks to provide torque multiplication through ratio advantage by utilizing the gear train mechanism and/or the end transmission means. [00024] The present subject matter seeks to reduce the size of the traction motor for the same torque output as compared to corresponding hub motor. [00025] The present subject matter seeks to ease serviceability of the vehicle by providing for easy attachment and detachment of the traction motor.

[00026] The present invention presents some of the following advantages including low vehicle weight and low cost, minimal changes to existing vehicle layout, reduced fuel consumption, improved efficiency, and better optimization. Additionally, the hybrid system can be optimized at conditions of low speed, heavy load or gradient surface to improve fuel efficiency. The traction motor is retrofittable and can function independently of the IC engine. Further, torque multiplication is obtained by utilizing the gear train mechanism and/or the end transmission means. [00027] The above functionalities are achieved by providing a saddle type hybrid vehicle comprising an IC engine having a crankshaft configured to receive rotary motion on burning of air and fuel mixture within the IC engine; an output shaft configured to receive rotary motion from the crankshaft, said output shaft operably connected to provide rotary motion output to a rear wheel of the saddle type vehicle; a first transmission mechanism interposed between the crankshaft and the output shaft, said first transmission mechanism configured to provide variable torque rotary motion output at the output shaft. As per an embodiment of the present invention, an electric motor unit is detachably mounted on an external surface of the IC engine, and is operably connected to the output shaft to provide independent and parallel rotary motion output at the output shaft along with the IC engine.

[00028] Further, the electric motor unit comprises an electric traction motor to provide rotary motion output, a second transmission mechanism interposed between the electric traction motor and the output shaft to provide variable torque rotary motion output at the output shaft, a first housing member and a second housing member assembled to form a space to accommodate the electric traction motor and the second transmission mechanism. The second transmission mechanism comprises of a motor shaft extending outward from the electric motor unit to be operably connected with the output shaft, a second one way clutch mounted on the motor shaft within the electric motor unit to permit rotary motion only from the electric traction motor to the output shaft.

[00029] The present invention along with all the accompanying embodiments and their other advantages would be described in greater detail in conjunction with the figures in the following paragraphs.

[00030] Fig. 1. illustrates a left side view of an exemplary two-wheeled step- through type vehicle, in accordance with an embodiment of present invention. Said vehicle (100) has a mono-tube type frame assembly (105) extending from a front portion (F) to a rear portion (R) along a longitudinal axis (F-R) of said saddle type vehicle (100). Said frame assembly (105) acts as a skeleton of said vehicle. The frame assembly

(105) extends from a head tube (108) in the front portion (F) of the vehicle till the vehicle rear portion (R). A steering shaft (not shown) is inserted through the head tube (108) and a handle bar assembly (115) is pivotally disposed on it. The steering shaft is connected to a front wheel (110) by front suspension(s) (120). A front fender (125) is disposed above the front wheel (110) for covering at least a portion of the front wheel (110). A fuel tank (130) is mounted on a rearwardly and downwardly extending member of the frame assembly (105), said member extending from the head tube (108). The frame assembly (105) forms a substantially horizontal step-through portion (106) with a floorboard to enable step-through mounting of a rider and to assist in carrying heavy loads. The IC engine (101) is mounted on the frame assembly (105) below the step- through portion (106) forming a low slung engine mounting. In an embodiment, a piston axis of the engine is horizontal i.e. parallel to a longitudinal axis of said vehicle (100). A swing arm (140) is swingably connected to the frame assembly (105). A rear wheel (145) is rotatably supported by the swing arm (140). One or more rear suspension(s) (150) are provided for ensuring riding comfort. Said rear suspension(s) are connected to the swing arm (140) at one end and to a portion of a rear frame member of the frame assembly (105) at the other end. A rear fender (155) is disposed above the rear wheel (145). A seat assembly (160A, 160B) is disposed rearwardly of the step-through portion

(106) for seating of the rider. In an embodiment, the seat assembly (160) includes a rider seat (160A) and a pillion seat (160B). Further, the seat assembly (160) is positioned above the rear wheel (145).The vehicle is supported by a centre stand (170) mounted to the frame assembly (105). The IC engine (101) is connected to the rear wheel (145) through a transmitting means. In one embodiment, the transmitting means includes an engine sprocket (414) which is linked to the rear wheel (145) through a chain drive (shown in Fig.4).

[00031] Fig. 2a illustrates a side view of the IC engine (101) and Fig. 2b. illustrates the top view of the IC engine in accordance with an embodiment of the present invention. The IC engine (101) is made up of a cylinder head (203), cylinder block (204), crankcase (210) and a cylinder head cover (202). The crankcase (210) is made up RH crankcase (210a), LH crankcase (210b), and a clutch cover (210c). The crankcase (210) houses the kickstarter assembly (not shown) and comprises the kickshaft (220) (shown in Fig.2b) which is connected to a ratchet mechanism (not shown). When the kickshaft (220) is actuated by the foot of a rider, the ratchet moves and engages with another ratchet operably connected to the crankshaft (407) (shown in Fig.3) via a starter gear train (404) (shown in Fig.3). On withdrawal of pressure from the foot, the return spring withdraws the kickshaft to starting position.

[00032] The clutch cover (210c) is disposed on the left hand side of the IC engine (101) adjacent to the LH crankcase (210b) and encloses a first centrifugal clutch (421) (shown in Fig.3) and related transmission gear mechanisms. The IC engine (101) includes an air intake system (205, 206), and an exhaust system (not shown). The RH crankcase (210a) encloses a wet magneto assembly (406) disposed on the right hand side (407a) (shown in Fig.3) of the crankshaft. The wet magneto assembly (406) is configured to rotate along with the crankshaft to generate power which recharges a battery. Further, a centrifugal fan is disposed in front of the magneto assembly (406) forming part of a cooling system to cool the IC engine (101). A shroud (402) encloses the centrifugal fan (405) (shown in Fig.3) and covers the cylinder head (203) and cylinder block (204). The centrifugal fan (405) rotates along with the crankshaft and draws atmospheric air inside and circulates it throughout the interior portions of the shroud (402). The IC engine (101) as per an aspect of the present invention supports an electric motor unit (201).

[00033] As per one embodiment, the electric motor unit (201) is disposed adjacent to the clutch cover (210c) and mounted on it. The clutch cover (210c) and the electric motor unit (201) comprises plurality of bosses (212) which are disposed at regular intervals around each of their outer peripheries. In the present embodiment said bosses (212) include holes to receive fasteners. The electric motor unit (201) is mounted on the clutch cover (210c) through said plurality of bosses (212) and is secured thereto through with fasteners. Besides aiding in mounting said motor unit (201) on the clutch cover (210c), said bosses (212) also aid in accommodating the engine sprocket (414) in a space between the electric motor unit (201) and the clutch cover (210c). Particularly, said bosses (212) are made to have sufficient length to in order to accommodate the engine sprocket (414).

[00034] Fig. 3. illustrates a cross sectional view of the internal combustion engine (101) and the electric motor unit (201) according to an embodiment of the present subject matter. The IC engine comprises a reciprocating piston (401) reciprocating within the cylinder block (204), and a crankshaft (407). Combustion occurs when air fuel mixture is burnt in the combustion chamber (422), resulting in transfer of pressure created during combustion to the reciprocating piston (401). The reciprocating motion of the piston is converted to rotary motion of the crankshaft (407) having a right hand side (407a) and a left hand side (407b); by a connecting rod (403) through a slider crank mechanism. The rotary motion of the crankshaft (407) is transferred to the engine sprocket (414) through a transmission system including a first transmission mechanism. The first transmission mechanism comprises a first centrifugal clutch (421) disposed on the left hand side (407b) of the crankshaft (407). A first driving gear (411) is freely mounted to the crankshaft (407) and connected to the crankshaft by the first centrifugal clutch (421). The first centrifugal clutch (421) is designed to engage only at a particular rotational speed of the IC engine. This rotational speed is usually just above idling rotational speed configured and designed for the IC engine. Hence, if the throttle is not operated by the rider, rotational speed of the IC engine decreases to idling speed and the transmission system is disengaged from the crankshaft (407). Once, throttle is operated, the first centrifugal clutch (421) engages, and the rotary motion is transmitted to the rest of the transmission system. Once, the vehicle speed is above idling speed and the first centrifugal clutch (421) is engaged the rotary motion is transferred to the first driving gear (411). The first driving gear (411) is meshed with a first driven gear (412), and the transmission ratio between the first driving gear (411) and first driven gear (412) provides the first speed reduction for the IC engine. The first driven gear (412) is disposed on an output shaft (415) and mounted on bearings. This gear train setup provides the transmission ratio operable for the engine. The first driven gear (412) is mounted on a first one way clutch (413) to prevent the rotary motion drive from transferring back to the crankshaft (407b) from the output shaft (415). Particularly, as per an embodiment of the present invention, the engine sprocket (414) which is disposed at one end of the the output shaft (415) and outside the LH clutch cover (210c) receives rotary motion from the output shaft (415) of the transmission system. As may be seen in Fig.4. a chain (301) connects the engine sprocket (414) to a corresponding wheel sprocket (302) on the rear wheel (145). This way rotary motion is transferred to the rear wheel (145). Further, as shown in Fig.3, the engine sprocket (414) comprises an outer gear teeth portion and an inner annular portion (414a) comprising internal splines and which is configured to receive a motor shaft (425) from the electric motor unit (201). A part of the motor shaft (425) projects outwards and comprises external splined portion (415a) which correspond to the internal splines on the engine sprocket (414). Similarly, the output shaft (415) of the transmission system of the IC engine (101) comprises external splined portion (425a). Thus, the engine sprocket (414) receives the output shaft (415) from one end and the motor shaft (425) of the electric motor unit (201) from the other end. For example, in the present embodiment said engine sprocket (414) receives the output shaft (415) from the right side and the motor shaft (425) of the electric motor unit (201) from the left side.

[00035] Fig. 4. and Fig.5 illustrate exploded views depicting mounting of the electric motor unit (201) to the IC engine (101) according to one embodiment of the present subject matter. Further the functional and operational aspects involved in the working of the electric motor unit (201) are also explained with respect to Fig.4 and Fig.5.

[00036] The electric motor unit (201) as per an embodiment of the present subject matter comprises an electric traction motor (420) (shown in Fig.5) to provide rotary motion output connected to the output shaft (415) through connection to the engine sprocket (414). The electric motor unit (201) also includes a second transmission mechanism (450) (shown in Fig.3) interposed between the electric traction motor (420) and the output shaft (415) to provide variable torque rotary motion output at the output shaft (415). The second transmission mechanism (450) comprises the motor shaft (425) extending outward from the electric motor unit (201) to be operably connected with the output shaft (415); and a second one way clutch (417) mounted on the motor shaft (425) within the electric motor unit (201) to permit rotary motion only from the electric traction motor (420) to the output shaft (415). A first housing member (201a) and a second housing member (201b) is assembled from either side to form a space therein to accommodate the electric traction motor (420) and the second transmission mechanism (450).

[00037] In the forgoing paragraphs two different embodiments of the present invention is described. [00038] As per a first embodiment of the present subject matter the electric motor unit (201) is disposed beyond the clutch cover (210c). The electric motor unit (201) provides the electric drive mode to be engaged. The second transmission mechanism (450) in the first embodiment comprises the motor shaft (425) and the second one way clutch (417). The electric traction motor (420) is mounted on the motor shaft (425) and transfers the rotary motion output during operation to the engine sprocket (414) through a second one way clutch (417) to permit rotary motion only from the traction motor (420) to the engine sprocket (414) and not vice versa. The motor shaft (425) is supported within the electric motor unit (201) by two roller bearings (419a & 419b) on either side of the electric motor unit (201). This arrangement ensures that, the traction motor (420) provides parallel rotary motion output at the engine sprocket (414) along with the first transmission mechanism (411, 412). The traction motor (420) comprises of a circularly disposed stationary stator core (420a) fixed to the motor shaft (425), and coaxially mounted ring shaped rotor core (420b) freely mounted to the motor shaft (425) over the stationary stator core (420a). The rotor core (420b) has a rotor hub (420c) attached to the second one way clutch (417), which in turn is operably mounted to the motor shaft (425).

[00039] A second embodiment of the present invention is explained with reference to Figs.6a-9. The electric motor unit (201) comprises the second transmission mechanism (450) in accordance with the second embodiment of the invention. Figures 6a-7 depict the location and mounting of the electric motor unit (201) which is the same as that explained in the earlier paragraphs. As may be seen in Fig.8 and Fig.9, the second transmission mechanism (450) in the second embodiment comprises of the motor shaft (425), an intermediate shaft (416) mounted parallel to the motor shaft (425), and said electric traction motor (420) is mounted on the intermediate shaft (416). The intermediate shaft (416) is supported by a pair of second roller bearings (432a and 432b), each of said pair of second roller bearing is disposed on the first housing member (201a) and the second housing member (201b) above the pair of first roller bearings (419a and 419b). [00040] A second driving gear (430) is rigidly mounted on said intermediate shaft (416) and meshed with a second driven gear (431) rigidly mounted on said motor shaft (425). Hence, in this arrangement, there is a geartrain arrangement between the electric traction motor (420) and the motor shaft (425) to vary torque output. This provides a torque multiplication due to the ratio increase because of the geartrain arrangement (second driving gear 430, second driven gear 431). The advantages of the second embodiment are that, a smaller capacity electric traction motor can be used as compared to the first embodiment due to the advantage obtained with the torque multiplication. The traction motor (420) comprises of the circularly disposed stationary stator core (420a) fixed to the intermediate shaft (416), and coaxially mounted ring shaped rotor core (420b) freely mounted to the intermediate shaft (416) over the stationary stator core (420a). The rotor core (420b) has a rotor hub (420c) attached to the second driving gear (430), which in turn is securely mounted to the intermediate shaft (416).

[00041] The invention is preferably applicable for hybrid two or three wheeled saddle type vehicles with small engines. In IC engines having capacity less than or equal lOOcc, the present invention offers advantages of low cost, and less weight. Such hybrid vehicles implementing the present invention are advantageous in such small vehicle as they permit easy maneuvering and handling during stop and go traffic conditions, as well as contribute to less cost and less weight. However, the present invention can also be applicable for higher capacity engines.