Gear Transmission for a Motorcycle

Field of invention

The present invention relates to "Gear transmission for a motorcycle" and more particularly, to a transmission system having plurality of pre-selectable transmission gear ratios.

Description of the prior art

There are a number of compact vehicles that need to have "single gear ratio" or "single speed" transmission for ease of driving and for increased utility. These include mopeds, scooters and other small automobiles. These vehicles generally have common requirements for low cost, high efficiency, good controllability throughout the entire speed range.

However, a trade-off between torque requirement and fuel economy is difficult to achieve as these requirements varies with the vehicle vocation. For instance a transmission ratio suited for high torque requirement may render the vehicle less fuel economic even when high torque is not required and vice-versa.

Therefore, a principal object of this invention is to provide a pre selectable geared transmission which accommodates the range of vehicle needs with a basic design approach, and provides for the adapting of different vehicle requirements while retaining many key transmission components across a range of vehicles.

Brief description of the invention

Accordingly, the present invention provides a transmission system that allows manual pre selection of transmission gear ratios as per the application requirements, from plurality of transmission gear ratios available, wherein each transmission gear ratio being operable over the entire speed range of vehicle.

In a preferred embodiment the present invention utilizes a first and second gear differing in number of teeth, turning independently on an output shaft having a keyway. The first gear is being driven by an output drive gear of a centrifugal clutch coupling the transmission system to an engine. The second gear being driven by the first gear through an intermediary gear positioned rotatably on another shaft laid parallel to the output shaft. The output shaft can be driven, by either said first gear or second gear at a time, engaged by an axially slide-able key mounted in said keyway and having projection in shape of "plus" symbol, which alternatively engage recesses provided on the first and the second gears. The output shaft in turn drives the wheel through a chain drive or by any other appropriate drive means. The axially slide-able key is manually operable to select one of the said two gear ratios at a time when centrifugal clutch coupling the crankshaft and transmission system is disengaged and the gears are not rotating. However, the transmission system may even have more than two gear ratios as per the vehicle design requirements.

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

Figure 1 illustrates a step through type two-wheeled vehicle using pre-
selectable gear transmission of the invention.

Figure 2 illustrates a cross-sectional view of an engine used in vehicle shown
in figure. 1.

Figure 3 illustrates in detail the pre-selectable gear transmission system as
per an embodiment of the invention.

Figure 4 and Figure 5 illustrate the constructional details of gears used in the
pre-selectable gear transmission system as per an embodiment of the
invention.

Detailed description of the preferred embodiment

Figure 1 shows a step-through type two-wheeled vehicle 01 having an engine 02 with a manual pre selectable transmission of the present invention. As shown in Figure 1 the illustrated engine 02 is a four-cycle single cylinder engine comprising a crankcase 03 and a cylinder block 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. Further, cylinder head 05 is secured to upper surface of the cylinder block 04. The crankshaft 06 housed in and supported by crankcase 03 is connected to a piston 07 positioned slide-ably within the cylinder bore of cylinder block 04 via connecting rod 08. The engine has a transmission system 10 on the left connected to the output of the crankshaft 06 through a centrifugal clutch 09.

In an embodiment of the invention the said transmission system 10 provides two pre selectable gear ratios each operable over the entire speed range of vehicle.

In a preferred embodiment the present invention utilizes a first driven gear 11, a first idler gear 11A and a second driven gear 12. The first driven gear 11 and second driven gear 12 differing in the number of teeth and having high speed and low speed drive ratios, are provided a little separated from each other in the axial direction on an output shaft 13 along with the first idler gear 11A placed between them. The first driven gear 11 and the second driven gear 12 can turn independently on said output shaft 13 also having a keyway 13A. The first driven gear 11 and the first idler gear 11A also differing in number of teeth are conjoined, being rotatable together wherein, the first driven gear 11 is driven by the drive gear 09A of said centrifugal clutch 09 and the first idler gear 11A drives second idler gear 14A having same number of teeth. The said second idler gear 14A is conjoined with an intermediary gear 14 differing in number of teeth being rotatable together wherein, the first 11A and second idler gear 14A acts as idler gear pair changing direction of rotation whereas, the intermediary gear 14 drives the said second gear 12. The intermediary gear 14 along with the second idler gear is positioned rotatably on secondary shaft 15. The secondary shaft 15 is laid parallel to the output shaft 13 in such a manner that the first idler gear 11A mates with the second idler gear 14A and intermediary gear 14 mates with the second driven gear 12. The said first driven gear 11, second driven gear 12, intermediary gear 14 and the idler gears rotates with the drive gear 09A of centrifugal clutch 06 at all times.

The output shaft 13 can be driven, by either of said first gear 11 or the second gear 12 at a time, by engaging an axially slide-able key 16 mounted in said keyway 14 and having a projection 16A in shape of "plus" symbol that alternatively engage recess 17, on the inner periphery of the first driven gear 11 and a recess 18 provided on the extended boss 12A of the second driven gear 12. The output shaft 13 in turn drives the wheel through a sprocket 19 connected at an end through a chain drive or by any appropriate drive means. The axially slide-able key 16 is manually operable to engage either first gear 11 or second gear 12 through the said projection 16A.

A manually operable actuating member 20 is provided that is movable between first and second position. Wherein at first position the first gear 11 is engaged with the output shaft 13 and is rotated by the first gear 11 and the second gear 12 rotates freely, in such case less torque is transmitted to the wheel and vehicle runs in economy mode, however when actuating member is moved to second position the second gear 12 is engaged with the output shaft 13 and first gear 11 keeps rotating freely in this case more torque is transmitted to the wheel and the vehicle runs in power mode however, this shift between the gears can be made only when the centrifugal clutch is disengaged and gears are not rotating, as no means to disengage the crankshaft output 06 from the transmission 10 is provided during vehicle running. In an embodiment, the gear ratio obtained ranges from 3 to 6 to get an overall ratio ranging from 13 to 18. This maintains the requirements for low cost, good controllability at the same time high efficiency can be achieved.

The above explained preferred embodiments are exemplary of the invention of the present application, which is described solely by the claims appended below. It should be understood that modifications of the preferred embodiments might be made as would occur to one of skill in the art, such as more than two transmission gear ratios can be used depending on the vehicle design requirements.

Claims

We claim:

1. A vehicle having a frame, a four-cycle engine mounted on the said
frame and at least two operational wheels comprising;

a transmission system operatively coupling the said engine with at
least one of the said wheels;

said transmission being a gear transmission with at least two pre-
selectable operational modes, each mode operable over the entire
speed range of vehicle;

said transmission being connected to the engine through a centrifugal
clutch having an output drive gear; and

a gear shift element having a manual actuating member, said actuating
member being movable between two positions for changing said gear
transmission between said modes.

2. The motorcycle as claimed in claim 1, wherein, said gear transmission
comprises;

an output shaft having first and second gear freely rotatable on the shaft adopted to engage the shaft through a key positioned slide-ably in the said output shaft actuable by the said gear shift element through the said manual actuating member;

said first gear being engaged with the said drive gear of the centrifugal clutch;

said first gear and second gear being engaged, through a secondary
gear; and

said output further having a means to couple at least one of the said wheels. 3. A motorcycle having the gear shift element as claimed in claim 1.