Transmission system for a motorcycle

Field of the invention

This invention relates to "Transmission system for a motorcycle" and in particular, to
a drive mechanism for said transmission system.

Description of the prior art

Most motorcycles have an engine mounted on a frame for driving the rear wheel of the motorcycle. To provide suspension for the rider, the rear wheel moves up and down angularly on a substantially horizontal swinging structure that is pivotally mounted to the motorcycle frame. Shock absorbers or springs are located between the swinging structure and the frame to dampen the up and down motion. Generally, a gear transmission is followed by a drive mechanism located between the engine and the rear wheel to transmit power from the engine to the rear wheel.

The drive mechanism connects the drive shaft of the engine to the rear wheel. The commonly, used drive mechanism includes a primary gear pair for reduction followed by a chain drive where a chain transfers torque from a sprocket wheel on a drive shaft of the engine to a sprocket wheel on the rear wheel axle or belt drives mainly use CVT as primary reduction wherein, a belt is used to transmit torque to the gear box then to rear wheel.

It is desirable for the drive mechanism to operate in a reliable and quiet manner.
However, the difficulties with chain drive mechanisms are that they are noisier, bulky,
have short life and require frequent external lubrication as well as adjustment,
whereas the belt drives have very low efficiency and short life.

Thus, it is an object of this invention to provide a motorcycle with a reliable, quiet and simple shaft drive mechanism that solves aforementioned problem.

Brief description of the invention

Accordingly, the invention provides a motorcycle having an engine, a frame on which
the engine is mounted such that there is no relative motion between the engine drive
shaft and rear wheel axle, the drive shaft extending from the engine transversely to
direction of travel, a rear wheel axle and a shaft drive mechanism extending
longitudinally from the drive shaft to the rear wheel axle for transmitting power from
the drive'shaft to the rear wheel axle.

A drive gear is located on the drive shaft for rotation thereby and an axle gear is located on the rear axle for driving the rear axle. A pinion shaft is provided and supported by a housing so as to be rotatable about its longitudinal axis, the pinion shaft having a front pinion gear meshing with the drive gear and a rear pinion gear meshing with the axle gear so that when the drive shaft is driven by the engine wherein, the drive gear is a multi-strut worm gear and front pinion gear meshing with the drive gear is a corresponding worm wheel, the axle gear and the rear pinion gear are bevel gears forming a bevel gear pair.

In the preferred embodiment said first end portion of the housing encloses the drive gear and said front pinion gear to hold oil for lubrication thereof and said second end portion of the housing encloses the axle gear and said rear pinion gear to hold oil for lubrication thereof.

Further, scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art.

Brief description of drawings

The invention will be more fully understood with reference to the following description
and drawings in which.

FIG. 1 is a prospective view of a motorcycle showing a shaft drive mechanism in accordance with a preferred embodiment of the invention.

FIG. 2 is a top view of the shaft drive mechanism shown in FIG. 1

FIG. 3 is a side view of the shaft drive mechanism shown in FIG. 1.
Detailed description of the preferred embodiment

Reference is made to FIG. 1, which illustrates a step through type, two-wheeled vehicle 01 having a shaft drive mechanism in accordance with the preferred embodiment of the invention. While the illustrated vehicle comprises a scooter, certain features, aspects and advantages of the present invention may also find utility with other types of vehicles.
The illustrated engine 02 mounted in a swingable manner comprises a crankcase 03 and a cylinder head 04 that is connected to the front end of the crankcase 03. In one configuration, the cylinder 04 preferably protrudes forward from a forward end of the crankcase 03 in a generally horizontal orientation such that it has an axis that extends in a longitudinal direction of the engine 02. Power is transferred from the engine 02 through the shaft drive mechanism 05 to a rear wheel 06. The rear wheel 06 has an axle shaft 07, which is rotatably supported by the rear end of the crankcase 03. The rear wheel 06 swings with the engine unit 02 and its motion is damped by shock absorbers 08 thereby providing suspension for the rider. As the engine 02 is swingable there is no relative motion between the engine drive shaft and the wheel axle 07.

FIG. 2 shows a pinion shaft 09 that is used to transfer power from the drive shaft 10 to the rear axle 07. The crankcase 03 comprises pinion shaft housing, drive gear housing, and an axle housing, all of which form an integral sealed structure. Oil is kept in the housings to keep the shaft drive mechanism lubricated. A drive gear 11 is located on the drive shaft 10 for rotation thereby and an axle gear 12 is located on the rear wheel axle 07 for driving the rear wheel axle 07. The pinion shaft 09 is supported by the crankcase 03 so as to be rotatable about its longitudinal axis, the pinion shaft 09 comprises a front pinion gear 11A meshing with the drive gear 11 and a rear pinion gear 12A meshing with the axle gear 12. In operation, the engine drives the drive shaft 10 through a centrifugal clutch 13 that engages at a predetermined rotational speed of the engine 02 and transfers torque from the crankshaft to the drive shaft 10 that in turn rotates a drive gear 11 secured to the said shaft. The drive gear 11 is a worm gear that engages with the front pinion gear that is a corresponding worm wheel 11A, so that when the drive shaft 10 is driven by the engine, the force applied by the drive gear 11 to the front pinion gear 11A creates a first moment on the pinion shaft 09 about the drive shaft 10. Thus, the pinion shaft 09 is rotated causing a rear pinion gear 12A to turn a meshing bevelled axle gear 12. The axle gear 12 is mounted on the rear wheel axle 07 and therefore the rear wheel is driven in a forward direction.

In an embodiment, where single stage gear reduction is used the worm gear 1T and worm wheel 11A at the engine end provides the desired gear ratio in comparatively lesser space eliminating the need for separate reduction gear pair whereas, the bevel gear pair at the rear wheel end provides desired angle between the pinion shaft 09 and the rear wheel axel 07. In such case the drive and the driven gear ratio obtained ranges from 3 to 5 and the overall ratio obtained ranges from 8 to 15. It should be understood that the foregoing description is that of a preferred embodiment of the invention and that various changes and modifications may be made without departing from the spirit and scope of the invention, as defined by the appended claims. The drive system can be used with other engine configurations and any other type of transmission system.

Claims:

We claim:

1. A four stroke internal combustion engine having a drive shaft extending from the engine transversely to direction of travel, a rear wheel axle and a shaft drive mechanism extending longitudinally from the drive shaft to the rear wheel axle for transmitting power from the drive shaft to the rear wheel axle, the drive mechanism comprising:

an elongate crankcase having a first end portion projecting from the rear end of cylinder block and receiving the crankshaft and a second end portion rotatably supporting the rear wheel axle;

a drive gear located on the drive shaft for rotation thereby wherein, the drive gear is a worm gear;

an axle gear located on the rear axle for driving the rear axle wherein, the axle gear
is a bevel gear;

a pinion shaft supported by the crankcase so as to be rotatable about its own longitudinal axis, the pinion shaft having a front pinion gear meshing with the drive gear and a rear pinion gear meshing with the axle gear wherein, the front pinion gear is a corresponding worm wheel and the rear pinion gear is a bevel gear;

said engine being mounted such that there is no relative motion between drive shaft and rear wheel axle.

2. A motorcycle having the engine as claimed in claim 1.