Motorcycle Frame Assembly

Field of the Invention:

This invention relates generally to motorcycle frame assembly and more particularly, relates to a main tube of the frame assembly for increasing stiffness.

Background of the Invention:

Two wheelers are very popular as means of transportation in ASIA. Chassis is a very critical part of a two wheeler taking most of the loads coming from the roads. During the design and development stage, stiffness of the frame needs to be established. Stiffness is one of the critical parameter, which decides the handling performance of the vehicle.

Apart from stiffness requirement recent days focus in the automotive industry is on energy, material saving and more environment friendly processes. One of the ways of achieving energy & material saving is by lighter vehicles. Weight cannot be reduced directly without any change in the design or in the processes. So newer techniques for developing light weight components & also reducing the number of components by integration of design are vital for future.

Therefore the challenge lies in producing light weight frame components without sacrificing stiffness and this challenge is addressed in the present invention.

Summary of the Invention:

An object of the present invention is to provide a main tube for motorcycle body frame with variable sections and variable thickness.

Another object of the present invention is to provide improved stiffness to the main tube of frame of motorcycle.

Another object of the present invention is to achieve weight reduction keeping the required stiffness.

Yet another object of the present invention is to reduce the welding length of the main tube.

Further object of the present invention is to achieve a better percentage elongation for the main tube.

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 from this detailed description.

Brief Description of the Invention:

The present invention will become more fully understood from the detailed description given herein below and the accompanying drawings which are given by way of illustration only, and thus are not limitative of the present invention, and wherein

Figure 1 shows a conventional motorcycle.

Figure 2 shows motorcycle frame assembly according to the present invention.

Figure 3 shows hydro- formed main tube according to the present invention.

Detail Description of the Invention:

With reference to figure 1 a motorcycle comprises of a frame (101), front fork (102) attached to a pivot tube (201) of the vehicle frame, a front wheel (103) attached to these front forks (102), a handle bar (104) connected to the front forks (102), a fuel tank (105) attached so as to straddle an upper part of the vehicle frame, a seat (106) attached to the upper rear portion of the vehicle frame, an engine unit (107) attached to the lower front section of the vehicle frame, a swing arm (108) attached to a lower rear section of the vehicle frame, suspended by a rear shock absorber (not shown) from the vehicle frame and a rear wheel attached to a rear end of swing arm (108). The intake system of the engine comprises of a fuel air metering device such as a carburetor (109), intake duct and an air cleaner. The exhaust system of the engine comprises of exhaust pipe and a muffler. The motorcycle is also provided with a side cover for covering a side section of the vehicle frame, a seat cover for covering a rear section of the vehicle frame below the seat, a front fender (110) for covering an upper part of the front wheel (103), and a rear fender (111) for covering an upper part of the rear wheel (112). The drive from the engine (107) is transmitted from the engine to the driven wheel sprocket mounted on the rear wheel hub mounted on the rear wheel assembly.

According to one embodiment of the present invention and referring to figure 2, the body frame of the motorcycle includes a head pipe/ steering pivot/pivot tube 201 at the front end of the body frame. From the top portion of the head pipe one main tube 202 extends backwards and obliquely downwards. Both sides of the lower portion of the main tube is provided with a bracket 203 for rear engine mounting. A tube
centre stand is disposed horizontally at the lower portion of the main tube 202, extending outward through an opening on the two sides of the bracket.

From the lower portion of the head pipe 201 a pair of left and right down tubes 204 extends obliquely downward and backward, while extending parallel in the direction towards the rear engine mounting bracket. The end portion of the said down tubes 204 is welded to the said tube centre stand.

From the portion where the main tube 202 starts descending, a pair of upper tubes 205 extends backward and slightly upward towards the rear side of the upper tubes with respect to the horizontal direction.

A pair of side tubes 206 extending from a middle portion of the rear engine bracket and extending backward and upward, while extending parallel in a direction so as to get welded with the end rear portion of the upper tubes 205.

The pair of left and right body frame components such as the down tubes and upper tubes as mentioned above are firmly interconnected with a plurality of horizontal bridges stretching between the pair of pipes and along the width of the vehicle body.

Two reinforcing members one between the front end portions of the main tube and down tubes and the other just below the rear end of the upper tubes Conventionally, the main tube of motorcycle frame will be of uniform cross section throughout the axis of the tube. The maximum section which can be achieved is limited by perimeter and thickness of the base section that means percentage elongation is very less. Variable thickness cannot be achieved in the conventional method. Variable thickness is required because of stiffness requirements at different locations based on stress plot. The main tube 202 of the motorcycle is formed by hydroforming manufacturing process. Hydroforming uses fluid pressure in place of the punch in a conventional tool set to form the part into the desired shape of the die. For example, a typical load bearing member that would normally be made by pressing up to six different sections and joining by welding can be hydroformed as a single part. Considerable mass savings are possible through eliminating the flanges required for welding and using thinner material. Yet stiffness is maintained owing to the elimination of .the discontinuous weld joints. Tube hydroforming.is done with the pre-cut length of the tube with desired diameter. Tube is pre-bent to the required radius to accommodate in the hydroforming tool. After the bending the tube is either preformed or directly sent for hydroforming. At the beginning the two ends of the tube are sealed using the hydraulic cylinders. These cylinders axially feed the tube in the die cavity during the pressurized fluid flow in the tube. The process has to be optimized for fluid pressure, die design and sealing parameters to avoid failure modes like thinning, buckling, bursting and spring back of the tube.

The main tube 202 according to the present invention is formed by hydroforming process, various sections (can be seen clearly in figure 3) and variable thickness is achieved along the axis of the main tube. Reinforcement brackets 207 which are welded to the main tube are reduced in size thereby reducing the welding length with the main tube. Previously a connecting tube was provided to the main tube to increase stiffness, now by hydroforming the main tube there is no requirement of the connecting tube.

The hydroformed main tube 202 extending from upper portion of the head tube obliquely downward and backward has at least two sections at various locations along the axis of the main tube. The said main tube has preferably four sections along the axis of the main tube ( seen in figure 3), a first section, second section, third section and fourth section. The first section being smaller than the second section. The third section being smaller than the second section. The fourth section being smaller than the said third section. The various locations having different sections are having different cross sections as desired.

The main tube having first section is proximate to connecting part of pivot tube.

In hydroform frame integration of brackets not only helped in reducing the frame weight and it also resulted in reducing of the weld length. Reduction of weld length reduced the cost and indirectly improves the durability by eliminating effect of weld variation on the frame durability. In this method of hydroforming, the maximum section change done was 46 percent more than the base section because of thickness variation and percentage elongation.

The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the claims.

We Claim:

1. A motorcycle comprising a front fork supporting a front wheel of a motorcycle is supported to be
rotatable by a head pipe located at a front end portion of a body frame of the motorcycle; and

at least one hydroformed main tube extending from upper portion of the head tube obliquely downward and backward;

wherein the hydroformed main "tube has at least two sections at desired locations along the axis of the main tube.

2. The motorcycle as claimed in claim 1, wherein said main tube has preferably four sections along the axis of the main tube, a first section, second section, third section and fourth section. The first section being smaller than the second section. The third section being smaller than the second section. The fourth section being smaller than the third section.

3. The motorcycle as claimed in claim 2, wherein said the main tube sections along the axis of the tube have different cross sections.

4. The motorcycle as claimed in claim 2, wherein a portion of the main tube having first section is proximate to connecting part of pivot tube.

5. A motorcycle frame as substantially shown and described in the specification.