Motorcycle frame

Field of the invention

The present invention generally relates to a step through type two-wheeled vehicle frame and more particularly to a column structure for supporting an engine and a swing arm.

Description of the prior art

Motorcycles and scooters mainly used for commuting or business purpose generally comprise a backbone type frame. The frame comprises a steering head pipe that supports a front fork. The frame also comprises a main frame member formed of a single tubular structure that extends rearward from the steering head pipe. In such vehicles, the main frame member typically forms the primary frame structure wherein, a column structure protruding downwards is provided on an intermediate portion of the main frame member. The column structure on the rear side supports a swing arm pivotally, to which a rear wheel is secured and on the front side, brackets can be provided to support the engine that is suspended from the main frame member.

A drive shaft extending from the engine transversely to direction of travel drives a rear wheel axle through a drive mechanism extending longitudinally from the drive shaft to the rear wheel axle for transmitting power. As can be imagined, the brackets generally protrude downward from the main frame member and forward from the column structure, a space is defined between the rear face of the crankcase and the column structure and this space is generally the same as the length of the brackets. When the motorcycle is viewed from the side, this space is generally enclosed by the brackets. Accordingly, the distance between the drive shaft and the pivot point of swing arm, which is on other side of the column structure, is determined by this arrangement. However, it is desirable that the distance between the drive shaft and the pivot point of the swing arm be minimized for optimum results.

Brief description of the invention

It is, therefore, an object of certain embodiments of the present invention to provide a column structure for a motorcycle that allows the distance between the drive shaft and the pivot point of swing arm to be reduced while still maintaining the strength of the column structure.

Accordingly, one aspect of the present invention involves a motorcycle that comprises a steering head pipe with a main frame member extending from the head pipe, firstly, obliquely downwards, secondly, rearwards parallel to the ground defining first horizontal structure, thirdly, obliquely upwards, and finally, rearwards parallel to the ground defining second horizontal structure, said main frame member is further formed of a single tubular structure. The column structure protrudes downwards from the rear end of the first horizontal structure comprising bracket designed to support the engine and having edges complementary to the profile of the rear face of crankcase along with a L-shaped tubular structure to add strength to the structure. This arrangement helps in reducing the distance between the drive shaft and the pivot point of the swing arm as the engine can be shifted towards the column structure.

Brief description of the drawings

Figure 1 illustrates a left side view of a moped, in accordance with the existing design.

Figure 2 illustrates a left side view, illustrating a backbone type frame used in the moped depicted in figure 1 along with a preferred arrangement of engine unit.

Figure 3 and Figure 4 are detailed view, illustrating the frame along with the column structure as per an embodiment of the invention.

Figure 5 illustrates a side view of the column structure bracket.

Figure 6 illustrates prospective view of the column structure bracket.

Figure 7 depicts the engine along with the crankcase.

Figure 8 and Figure 9 illustrates the arrangement of tubular structure and the drain hole.

Detailed description of the preferred embodiment

With reference to drawing Figures a moped 01 preferably comprising a backbone type frame is illustrated. While the illustrated vehicle comprises a moped or a motorcycle, certain features, aspects and advantages of the present invention may also find utility with other types of vehicles. In particular, certain features, aspects and advantages of the present invention may find utility with other vehicles having an engine suspended from a central frame member.

As illustrated the steering head pipe 03 is located at the front end of the frame 02. The steering head pipe 03 supports the front wheel 04 through the front fork 05 along with the handle bar 06 to steer the vehicle. A main frame member 07 extends firstly, obliquely rearwards and downwards 07A from the steering head pipe 03, secondly, rearwards parallel to the ground forming front horizontal structure 07B of the frame, thirdly, obliquely upwards and rearwards 07C and finally, rearwards parallel to the ground forming rear horizontal section 07D.

The main frame member 07 can be secured to the steering head pipe 03 in any suitable manner. The main frame member 07 preferably defines the primary structure of the frame 02 and can be made of any suitable material, such as, for example but without limitation, a steel pipe having a generally circular cross-section. In some configurations, the main frame member can have the shape of a box in cross section. Other materials and shapes also can be used.

Further, a column structure 15 is secured to the rear portion of the first horizontal structure 07B in any suitable manner, designed and configured to support a swing arm 12 on rear side and engine 09 on the front. The column structure 15 protrudes downwards from the first horizontal structure 07B of the main frame member 07. The swing arm 12 extends rearward of the column structure 15, and a rear wheel 11 is supported at the rear end of the swing arm 12. Preferably, at least a portion of the swing arm 12 is connected to the frame 02 through a shock absorber 13 or the like. The column structure 15 is formed of a bracket in shape of a C-letter wherein the open edges 15A and 15B faces forward direction of the vehicle and are spaced from each other in transverse direction of the vehicle, an arcute shaped relief 22 is provided on the first open edge 15B of the bracket 15 and a relief 23 having a substantially non-linear profile similar to a curly bracket or braces "}" is provided on the second one of the said edge 15A with a substantially circular profile 14 in centre. On both the open edges 15A and 15B top and bottom portion are provided with grooves 17 and 18 opposite to each other that can be used to bolt corresponding extended bosses provided on the rear face of the crankcase 19 to secure the engine 09. The size and location of the reliefs 22 and 23 are in accordance with the profile of the rear face of the crankcase 19.

Further, engine bracket 16 extending downwards from an intermediate location of the first horizontal structure 07B is provided. The illustrated engine comprises a crankcase 19 and a cylinder 20 that is connected to the front end of the crankcase 19. In one configuration, the cylinder 20 preferably protrudes forward from a forward end of the crankcase 19 in a generally horizontal orientation such that it has an axis that extends in a longitudinal direction of the engine 09.

The engine 09 has, for example, a four-cycle single-cylinder engine as a drive source and a crankcase 19 and a cylinder 20 that is connected to the front end of the crankcase 19. The crankcase 19 houses a crankshaft that extends generally horizontally in the transverse direction of the vehicle. The torque from the crankshaft is transmitted to the output drive shaft 25 of the transmission system, coupled through a centrifugal clutch to the crankshaft.

In an embodiment the crankcase 19 comprises extended bosses corresponding to the engine brackets having grooves for bolting, the first boss 24 protrudes upward from the forward end of a top face of the crankcase 19. The second 25 and third boss 26 protrude longitudinally from the rearward end of the top face of the crankcase 19. The first boss 24 is secured with the engine bracket 16 and second 25 and third 26 bosses interpose inside the spaced edges 15A, 15B of C-shaped bracket 15 and are bolted through the said grooves 17 and 18 correspondingly. As the extended bosses 25 and 26 are interposed inside the column bracket 15 no additional space is occupied by any extended brackets and further the profile of edges 22 and 23 accommodates the rear face of the crankcase lowering the distance D between the drive shaft 27 and the pivot point 28 of the swing arm 12.

Further a L-shaped tubular structure 21 is secured to the rear portion of the first horizontal structure 07B interposed between the spaced edges 15A, 15B of the-shaped bracket 15 such that the horizontal section forming the L-shape extends through the substantially circular profile provided at the centre of second one of the said open edge 15A, providing further strength to the column structure and resistance to vibration.

In an embodiment, a drain hole 26 is provided on the rear portion of the first horizontal structure 07B through the said tubular structure 21 that opens 27 at the joining of the vertical and horizontal tubular structures forming the L-structure 21. Although the present invention has been described in terms of a certain embodiment, other embodiments apparent to those of ordinary skill in the art also are within the scope of this invention. Thus, various changes and modifications may be made without departing from the spirit and scope of the invention. For instance, various components may be repositioned as desired. Moreover, not all of the features, aspects and advantages are necessarily required to practice the present invention. Accordingly, the scope of the present invention is intended to be defined only by the claims that follow.

Claims:

We claim:

1. A motorcycle comprising:

a steering head pipe;

a main frame member extending firstly, obliquely downwards secondly, rearwards parallel to the ground defining first horizontal structure and thirdly, obliquely upwards, and finally, rearwards parallel to the ground defining second horizontal structure;

said main frame member is formed of a single tubular structure;

a column structure having a first and a second sides spaced in transverse direction from each other and protruding downwards from a rear portion of first horizontal structure;

an engine comprising a case having a top face and a rear face having extended bosses;

the case being suspended from the main frame member and supported by the column structure through said bosses wherein, on one side the bosses on the rear face are interposed in the space between the said first and second sides of the column structure and the edges of the first and second side have profile complementary to the rear face of the case of the engine, on the other side a swing arm is pivotally secured to the column structure.

2. The motorcycle of claim 1, wherein the engine comprises a cylinder and a crankshaft, the crankshaft being positioned generally within the case, the cylinder projecting forward of a forward end of the case.

3. The motorcycle of claim 1, wherein a L-shaped tubular structure secured to the rear portion of first horizontal structure is interposed between the first and second sides of the column structure supporting the column structure.

4. The motorcycle of claim 3, wherein a L-shaped tubular structure secured to the rear portion of first horizontal structure is interposed between the first and second sides of the column structure supporting the column structure also provides a drain hole.