MOTORCYCLE BODY FRAME STRUCTURE

FIELD OF THE INVENTION

The present invention relates to a structure of motorcycle body frame and more particularly to the structure of the main tube of the motorcycle.

BACKGROUND OF THE INVENTION

All motorcycles utilize certain types of frame structure to carry stress and loads encountered during vehicle operation. Typically, a body frame of a motorcycle includes a head pipe, a main tube, including a main tube upper portion and a main tube lower portion, extending rearwards from said head pipe and then extending substantially downwards towards an engine mounting bracket mounted therein, a down tube extending downwards from the head pipe, a pair of upper tubes extending rearwards from the main tube, and a pair of side tubes extending forwardly downwards from the pair of upper tubes towards the main tube. Typically, the pair of upper tubes is connected to the main tube upper portion by means of a weld joint. Area of the main tube around the weld joint is subject to load from a fuel tank and is prone to fatigue and failure due to lateral movement of the weld joint. Further, a main tube lower portion is also subject to load from the pair of side tubes and a swing arm connected to the main tube lower portion through the engine mounting bracket. Thus, the main tube of body frame of the motorcycle acts as a principal load carrying member.

Body frame stiffness of the motorcycle affects dynamic handling of the motorcycle. Body frame stiffness is experienced by the rider when the body frame experiences a torsional moment. A torsional moment tends to twist the body frame, i.e. instilling a twist between the head pipe of the body frame and a swing arm pivot on the main tube of the body frame. Hence, the main tube of the body frame, which is subject to torsional moment, requires to be stiffened in order to minimise deflection due to torsional moment. This is particularly significant for maintaining dynamic handling of the motorcycle. It is therefore desirable to increase the stiffness of the main tube of the body frame of the motorcycle in order to minimise the torsional moment acting on the main tube and to improve dynamic handling of the motorcycle. In a known body frame structure of a motorcycle, the pair of side tubes is directly mounted to the engine mounting bracket welded to the main tube lower portion. Swing arm of the motorcycle is also mounted to the engine mounting bracket through a pair of swing arm boss. As a result, load from the pair of side tubes and the swing arm gets directly transferred to the engine mounting bracket.

In order to withstand the load transferred by the pair of side tubes and the swing arm and to stably support an engine unit, the engine mounting bracket is provided in the form of a bulky member, thereby leading to substantial increase in the weight of the body frame. It is therefore desirable to use the different existing elements of the -body■—■ - —-frame of a motorcycle effectively, to optimise the stiffness and weight of the body frame. Against the foregoing background, it is an object of the invention to provide enhanced stiffness to the main tube of the body frame of the motorcycle. It is another object of the invention to minimise torsional moment acting on the main tube due to movement of the swing arm.

SUMMARY OF THE INVENTION

The present subject matter disclosed herein is directed to a motorcycle body frame structure, wherein the body frame comprises a head pipe, a main tube including a main tube upper portion and a main tube lower portion, wherein the main tube upper portion extends rearwardly and substantially obliquely downwards from the head pipe, and the main tube lower portion extends downwardly from said main tube upper portion towards one or more top engine mounting members, a pair of upper tubes, including a front welded portion and a rear portion therein, wherein said front welded portion extends along sides of the main tube upper portion, and the rear portion extends rearwards from said front welded portion, a downtube extending downwards from the head pipe, and a pair of side tubes extending forwardly and obliquely downwards from said pair of upper tubes towards the one or more top engine mounting members

_._ Jocated on the main tube lower portion.,. As_per,Lhe.p,resentJ,n.ve.ntion,.tQp and bottom engine mounting members are secured to the main tube lower portion, in a manner such that the top engine mounting members together with a pair of swing arm boss, a pair of engine support boss, and the pair of side tubes, forming a junction, are jointly secured to the main tube lower portion substantially above the bottom engine mounting members. The pair of side tubes and a swing arm are connected to the top engine mounting members through the pair of swing arm boss. Since the pair of side tubes and the swing arm is connected to the top engine mounting members, the forces exerted by the pair of side tubes and the swing arm is significantly countered by the stiffness offered by an engine unit connected to the top engine mounting members. As a result, the need for providing a single bulky engine mounting member is eliminated, thereby enabling significant weight reduction of the body frame. Moreover, the disposition of the top engine mounting members in a manner described above also aids in stiffening the main tube lower portion and thereby aids in minimising the deflection of the body frame due to torsional moment acting on the main tube lower portion.

Further, a stiffener plate is also secured on a bottom surface of the main tube upper portion, bridging the front welded portion of the pair of upper tubes, thereby strengthening a weld joint area of the front welded portion of the pair of upper tubes on the main tube upper portion. Thus, the stiffener plate aids in stiffening the main tube upper portion. Therefore, while tine - overall-stiffness of the main tube is ensured with the aid of the top engine mounting members as well as the stiffener plate, the overall weight of the body frame is also optimised. The foregoing objective and summary provide only a brief introduction to the present invention. To fully appreciate these and other objects of the present invention as well as the invention itself, all of which will become apparent to those skilled in the art, the following detailed description of the invention and the claims should be read in conjunction with the accompanying drawings. Throughout the specification and drawings identical reference numerals refer to identical or similar parts.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 illustrates a typical motorcycle to which the present invention is applicable.

Figure 2 illustrates a side view of body frame for a motorcycle according to the present invention.

Figure 3 illustrates a stiffener plate secured on a bottom surface of main tube upper portion bridging a front welded portion of the pair of upper tubes of the body frame.

Figure 4 illustrates a perspective view of main tube lower portion, to which iop and bottom engine mounting members are secured in accordance to the present invention.

Figure 5 illustrates a perspective view of the main tube lower portion in accordance to the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Exemplary embodiments of a structure of body frame of a motorcycle, in accordance to the present invention will be described hereunder with reference to the accompanying drawings. Various features of the body frame structure in accordance to the present invention will become discernible from the following description set out hereunder. Rather, the following description provides a convenient illustration for implementing exemplary embodiments of the invention. It is to be noted that terms "upper", "lower", "right", "left", "front", "rear", "downward", "upward", "top", "bottom" and like terms are used herein based on the illustrated state or in a standing state of the motorcycle with a driver riding thereon. It is to be understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. Referring firstly to Figure 1, there is illustrated diagrammaticaliy a motorcycle 10. The motorcycle 10 includes a body frame 20 on which an engine 30 is mounted. A head pipe 22 is provided at a front end of the body frame 20. The head pipe 22 supports a steering shaft (not shown) rotatably in a certain range and a front fork 18 pivotally. In an upper portion of the head pipe 22, a handlebar 15 is rotatably integrally connected to the steering shaft. A front wheel 16 is joumaled to a lower end of the front fork 18 and the front wheel 16 is rotated in a certain range -by steering the handlebar 15.

In a front portion of the body frame 20 a fuel tank 35 is arranged immediately behind the handle bar 15 and is disposed over the engine unit 30. A seating seat is placed behind the fuel tank 35. The seating seat includes a front seat 37 and a rear seat 38. The front seat 37 is placed immediately behind the fuel tank 35, while the rear seat 38 is disposed in a slightly upper position behind the front seat 37. The engine unit 30 is supported to the body frame 20 by being suspended in a front lower portion of the body frame 20. The engine unit 30 is equipped with an exhaust system and includes an exhaust pipe (not shown) connected to the engine unit 30 and a muffler 36 connected to the exhaust pipe. The muffler extends rearwards along the right side of the rear wheel 40. Further, a swing arm 42 is swingably connected to a rear lower portion of the body frame 20 and extends rearwards. The rear wheel 40 is rotatably supported at a rear end of the swing arm 42. Power from engine unit 30 suspended in a front lower portion of the body frame 20 is transmitted to the rear wheel 40 through a power drive mechanism, such as a drive chain, so as to drive and rotate the rear wheel 40.

Figure 2 illustrates a body frame 20 for a motorcycle according to the present invention! The body frame 20 as per the present invention includes the head pipe 22, a main tube 23 extending rearwards from the head pipe 22, a downtube 24 extending downwards from the head pipe 22, a pair of upper tubes 26 extending rearwards from the main tube 23, a pair of side tubes 28 extending forwardiy and obliquely downwards from the pair of upper tubes 26. Further, said main tube 23 extending rearwards from the head pipe 22 includes a main tube upper portion 23a, a main tube lower portion 23b. Whereas the main tube upper portion 23a extends rearwardly and substantially obliquely downwards from the head pipe 22, the main tube lower portion 23b extends downwardly from said main tube upper portion 23a towards top engine mounting members 108a. The pair of upper tubes 26 includes a front welded portion 26a and a rear portion 26b, wherein the front welded portion 26a is welded to the main tube upper portion 23a and extends along sides of the main tube upper portion 23a, and wherein the rear portion 26b extends rearwardly and substantially obliquely upwards from the front welded portion 26a.

Furthermore, the pair of side tubes 28 extending forwardiy and obliquely downwards from the rear portion 26b of the pair of upper tubes 26, is Connected to the main tube lower portion 23b through a pair of swing arm boss 107 mounted therein. Swing arm 42 is also connected to the main tube lower potion 23b through the pair of swing arm boss 107. While the main tube upper portion 23a includes a stiffener plate 104 at its bottom surface 23ab, in an area where the front welded portion 26b of the pair of upper tubes 26 is welded to the main tube upper portion 23a, the main tube lower portion 23b includes top and bottom engine mounting members 108a and 108b to receive a top portion and a bottom portion of the engine unit 30 respectively. The top and bottom engine mounting members 108a and 108b respectively are provided with mounting holes to receive the mounting of an upper portion of the engine unit 30. In the present embodiment pair of top engine mounting members 108a are secured to the main tube lower portion 23b individually. In another embodiment the top engine mounting members 108a may be secured to the main tube lower portion 23b as a single unit.

Referring to Figures 3-5, the mounting of the stiffener plate 104 and that of the top engine mounting members 108a to the main tube upper portion 23a and the main tube lower portion 23b respectively may be explained. As may be seen in Figure 3, the stiffener plate 104 is secured to the bottom surface 23ab of the main tube upper portion 23a, in such a manner that it bridges a weld joint area of the front welded portion 26a of the pair of upper tubes 26. In the present embodiment, the stiffener plate 104 is secured to the main tube upper portion 23a by a forging process such as spot welding. However, in another embodiment, the stiffener plate 104 may be secured to the bottom surface 23ab of the main tube upper portion 23a by any other forging process. Thus, the stiffener plate 104 reinforces the weld joint area formed by the front welded portion 26a of the pair of upper tubes 26 on the main tube upper portion 23a. As a result, load bearing capacity of the of the main tube upper portion 23a is increased. Thereby, yielding of the main tube upper portion 23a due to fuel tank load or pillion rider load is avoided.

Figure 4 illustrates the top engine mounting members 108a as mounted to the main tube lower portion 23b. As may be seen in the figure, bottom engine mounting members 108b are secured to a lower section of the main tube lower portion 23b. A pair of swing arm boss 107 is mounted to the main tube lower portion 23b at a certain distance above the bottom engine mounting members 108b. A pair of engine mounting support boss 110 is also mounted to the main tube lower portion 23b at a certain distance above the pair of swing arm boss 107. Further, the pair of side tubes 28 extending forwardly and obliquely downwards from the pair of upper tubes 26 towards the main tube lower portion 23b, is mounted to the pair of swing arm boss 107 from a rear side. A swing arm 42 is also mounted to the pair of swing arm boss 107 such that the swing arm 42 lies on either side of the main tube lower portion 23b. The top engine mounting members 108a is secured on the main tube lower portion 23b between the pair of swing arm boss 107 and the pair of engine support boss 110, in a manner such that a first flange of the top engine mounting members 108a extends along the pair of swing arm boss 107, a second flange extends along the pair of engine mounting boss 110 and a third flange extends along a rear side of the main tube lower portion (as shown in Fig 5).

Further, an oblique edge of the top engine mounting members running above the first flange extends along the pair of side tubes 28, thereby bridging the pair of side tubes 28 with the top engine mounting members 108a. Thus, the top engine mounting members 108a, the pair of swing arm boss 107, the pair of engine support boss 110 and the pair of side tubes 28, which are jointly mounted with each other, form a junction substantially above the bottom engine mounting members 108b. Further, the top engine mounting members 108a are provided with mounting holes to receive the mounting of an upper portion of the engine unit 30. Thus, an area of the main tube lower portion 23b in which the top engine mounting members 108a, the pair of swing arm boss 107, the pair of engine support boss 110 and the pair of side tubes 28 jointly form a junction is sufficiently strengthened by the stiffness offered by the pair of side tubes 28 from one side, as well as the stiffness offered by the upper portion of the engine unit 30 from a second side. Thus, the present mounting and location of the top engine mounting members 108a eliminates the requirement for a single bulky engine mounting member, and thereby aids in reducing the overall weight of the body frame 20.

Further, the stiffening of the main tube lower portion 23b, thus obtained also helps in; countering the torsional^ moment acting on the main tube lower portion 23b due to the movement of the swing arm 42. Therefore, deflection of the body frame 20 due to action of torsional moment is also minimised, thereby improving the overall dynamic handling of the motorcycle. Motorcycle stability and manoeuvrability is also improved as a result. While the present invention has been shown and described with reference to the foregoing preferred embodiments, it will be apparent to those skilled in the art that changes in form, connection, and detail may be made therein without departing from the spirit and scope of the invention as defined in the appended claims:

WE CLAIM:

1. A body frame (20) for a motorcycle, said body frame (20) comprising: a head pipe (22); a main tube (23), including a main tube upper portion (23a) and a main tube lower portion (23b), extending rearwardly from the head pipe (22); a pair of upper tubes (26), including a front welded portion(26a) and a rear portion (26b), connected to the main tube (23); a pair of side tubes (28), wherein said pair of side tubes (28) extends from the rear portion (26b) of said pair of upper tubes (26) towards the main tube lower portion (23b); characterized in that: the main tube lower portion (23b) comprises one or more top engine mounting members (108a) and one or more bottom engine mounting members (108b), wherein the one or more top engine mounting members (108a), one or more swing arm boss (107), one or more engine support boss (110), and the pair of side tubes (28) are jointly mounted along with the main tube lower portion (23b) forming a junction substantially above the one or more bottom"-' engine mounting members (108b).

2. The body frame (20) as claimed in claim 1, wherein the pair of side tubes (28) is connected to the one or more top engine mounting members (108a) through the one or more swing arm boss (107).

3. The body frame (20) as claimed in claim 1, wherein the one or more top engine mounting members (108a) is connected to a swing arm (42) through the one or more swing arm boss (107).

4. The body frame (20) as claimed in claim 1, wherein the front welded portion (26a) of the pair of upper tubes (26) is bridged by a stiffener plate (104).

5. The body frame (20) as claimed in claim 1 or claim 4, wherein the stiffener plate (104) is secured on a bottom surface (23ab) of the main tube upper portion (23a), bridging the front welded portion (26a) of the pair of upper tubes (26).

6. The body frame (20) as claimed in claim 5, wherein the stiffener JDlate (104) is secured on the bottom surface (23ab) of the main tube upper portion (23a) by means of a forging process.

7. The body frame (20) as claimed in claim 5, wherein the stiffener plate (104) is U-shaped. 3. A motorcycle comprising the body frame (20) as claimed in claims