Frame Structure for a Motorcycle

1. Field of the Invention

The present invention relates to an improvement in a frame structure for pivotably supporting a swing arm in a motorcycle or the like wherein an engine is mounted on a body frame having a front end provided with a head pipe for supporting a front suspension, and a swing arm for supporting a rear wheel is pivotably supported at its front end to the body frame at a rear portion thereof behind the engine.

2. Description of Background Art

FIG. 7 illustrates a conventional frame structure for pivotably supporting a swing arm. A pair of left and right pipes 41 are welded to a rear portion of a single main pipe 16' connected to a head pipe 15. A pair of left and right supporting plates 25' are welded both to a pair of left and right down tubes 17' connected to the head pipe 15 and to the pipes 41. A pivot shaft, not shown, for supporting a swing arm, not shown, is provided between the left and right supporting plates 25'.

According to the above conventional structure, the pair of pipes 41 are welded to the single main pipe 16', and the pair of supporting plates 25' are welded both to the pipes 41 and to the pair of down tubes 17'. Accordingly, the length of the welding is large to cause an increase in cost of construction. The shaft working for the connection of the swing arm to the pivot shaft extending between the supporting plates 25' is carried out after connecting all of the parts of the body frame. Accordingly, a unit to be handled in shaft working for the connection of the swing arm to the pivot shaft is large in size, so that the operation of the shaft provided for the connection of the swing arm is not easy.

In Japanese patent publication No. 3-24394 there is disclosed a swing arm supporting structure having a pair of left and right supporting plates connected by three cross members and a pivot shaft provided between the left and right supporting plates. This swing arm supporting structure is fixed to a pair of left and right main pipes and a pair of left and right down tubes. Accordingly, the number of parts is increased.

It is accordingly an object of the present invention to provide a frame structure in a motorcycle or the like which can support a swing arm with a simple structure by reducing the number of parts and the length of welding. The connection of the swing arm to the body frame is made easier.

According to the present invention, there is provided in a motorcycle or the like with an engine mounted on a body frame having a front end provided with a head pipe for supporting a front suspension. A swing arm for supporting a rear wheel is pivotably supported at a front end of the swing arm to a rear portion of the body frame thereof behind the engine. A frame structure is provided wherein the body frame has a single main pipe comprising a rearwardly extending portion located over the engine and extending rearwardly from the head pipe. A bent portion extends from a rear end of the rearwardly extending portion. A downwardly extending portion is located behind the engine and extends downwardly from the bent portion. A pair of cross pipes laterally extend and are vertically spaced from each other and are connected at their intermediate portions to the downwardly extending portion of the main pipe. A pair of supporting plates are located so as to be interposed therebetween the downwardly extending portion of the main pipe which is connected to both ends of each of the cross pipes. The front end of the swing arm is pivotably supported to a pivot shaft located between the cross pipes and extending between the supporting plates.

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.

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

FIG. 1 is a side view of a motorcycle;

FIG. 2 is a side view of a body frame;

FIG. 3 is a plan view taken in the direction of an arrow 3 in FIG. 2;

FIG. 4 is a rear view taken in the direction of an arrow 4 in FIG. 2;

FIG. 5 is a perspective view of the body frame taken from a left front side thereof;

FIG. 6 is a cross section taken along the line 6--6 in FIG. 2, showing a swing arm supporting structure; and

FIG. 7 is a perspective view showing a body frame of the prior art.

A preferred embodiment of the present invention as applied to a motorcycle will now be described with reference to the drawings.

Referring first to FIG. 1, an engine E and a fuel tank T are mounted on a body frame 11 of the motorcycle. A front wheel W.sub.F is suspended through a front suspension 12 to a front end portion of the body frame 11. A rear wheel W.sub.R is supported to a rear end of a swing arm 13 pivotably supported to a rear lower portion of the body frame 11. A shock absorber 14 is interposed between the swing arm 13 and a rear upper portion of the body frame 11.

Referring to FIGS. 2, 3, 4, and 5, the body frame 11 includes a head pipe 15 for supporting the front suspension 12. A single main pipe 16 extends rearwardly from the head pipe 15. A pair of left and right down tubes 17.sub.1 and 17.sub.2 are connected to the head pipe 15 and extend below the main pipe 16. A pair of left and right seat rails 18 extending rearwardly from a rear upper portion of the main pipe 16. A joint portion disposed between the head pipe 15, the main pipe 16, and the down tubes 17.sub.1 and 17.sub.2 is reinforced by a gusset 19.

The main pipe 16 has a rearwardly extending portion 16a disposed over the engine E and extending rearwardly from the head pipe 15, a bent portion 16b extends from a rear end of the rearwardly extending portion 16a, and a downwardly extending portion 16c is disposed behind the engine E and extends downwardly from the bent portion 16b. Both of the seat rails 18 are welded at their front ends to the bent portion 16b of the main pipe 16. Reinforcing members 20 and 21 extend between the two seat rails 18. As illustrated in FIG. 1, a seat 22 is mounted on both of the seat rails 18. The shock absorber 14 is interposed between the seat rails 18 and the swing arm 13.

The down tube 17.sub.1 is composed of a first cylindrical portion 17a, a second cylindrical portion 17c, and a connecting member 17b connecting the first and second cylindrical portions 17a and 17c. The down tube 17.sub.1 has a substantially U-shaped configuration. The first cylindrical portion 17a is inclined downwardly from the head pipe 15, and a front end of the first cylindrical portion 17a is connected to the head pipe 15. The second cylindrical portion 17c is inclined upwardly from the connecting member 17b, and a front end of the second cylindrical portion 17c is connected through the connecting member 17b to a rear end of the first cylindrical portion 17a. A rear end of the second cylindrical portion 17c is connected to one of the two seat rails 18. The connecting member 17b also serves to support a stand, not shown.

The other down tube 17.sub.2 has basically the same shape as that of the down tube 17.sub.1, but the down tube 17.sub.2 is formed as an integral part. A front end of the down tube 17.sub.2 is connected to the head pipe 15, and a rear end of the down tube 17.sub.2 is connected to the other seat rail 18.

The main pipe 16, as a component of the body frame 11, includes a pair of upper and lower cross pipes 23 and 24 laterally extending and vertically spaced from each other which are welded at their intermediate portions to 10 the downwardly extending portion 16C of the main pipe 16. A pair of left and right flat supporting plates 25.sub.1 and 25.sub.2 are opposed to each other. The downwardly extending portion 16c interposed therebetween is welded to both ends of each of the cross pipes 23 and 24. Both of the cross pipes 23 and 24 are inserted through the downwardly extending portion 16c of the main pipe 16. In this inserted condition, the intermediate portions of the cross pipes 23 and 24 are welded to the downwardly extending portion 16c. The supporting plates 25.sub.2 and 25.sub.2 are welded to the down tubes 17.sub.1 and 17.sub.2 at their rear lower portions, respectively.

A supporting sleeve 26, inserted through the downwardly extending portion 16c of the main pipe 16, is located between the cross pipes 23 and 24 in a parallel relationship thereto. The supporting sleeve 26 is welded at its intermediate portion to the downwardly extending portion 16c. The supporting plates 25.sub.1 and 25.sub.2 includes through holes 27 aligned with opposite end openings of the supporting sleeve 26. An inner diameter of the supporting sleeve 26 is somewhat larger than the diameter of each through hole 27.

The supporting plates 25.sub.1 and 25.sub.2 are integrally formed at a front lower portion thereof with supporting portions 25a for supporting the engine E.

Referring to FIG. 6, the swing arm 13 is composed of a pair of left and right arms 13a and 13b and a connecting plate 13c connecting the arms 13a and 13b together. The front ends of the arms 13a and 13b are located between the supporting sleeve 26 and the left supporting plate 25.sub.1 and between the supporting sleeve 26 and the right supporting plate 25.sub.2, respectively. The arms 13a and 13b are pivotably supported by a bolt 28 as a pivot shaft provided between the supporting plates 25.sub.1 and 25.sub.2. More specifically, cylindrical specifically, cylindrical members 29a and 29b are aligned with each other and welded to the front ends of the arms 13a and 13b, respectively. A first sleeve 30 having the same diameter as that of the supporting sleeve 26 is located between one end of the supporting sleeve 26 and the supporting plate 25.sub.1. A needle bearing 31 is interposed between the first sleeve 30 and the cylindrical member 29a. Further, a second sleeve 32, having the same diameter as that of the supporting sleeve 26, is located to abut against the other end of the supporting sleeve 26. A third sleeve 33, having the same diameter as that of the supporting sleeve 26, is located to abut against an inner surface of the supporting plate 25.sub.2. An inner lace of a ball bearing 34 is interposed between the second sleeve 32 and the third sleeve 33. The ball bearing 34 is interposed between the cylindrical member 29b and the bolt 28. Thus, the bolt 28 is inserted through the through hole 27 of the supporting plate 251, the first sleeve 31, the supporting sleeve 26, the second sleeve 32, the inner lace of the ball bearing 34, the third sleeve 33, and the through hole 27 of the supporting plate 25.sub.2. A nut 35 is threadedly engaged with an end portion of the bolt 28 projecting from the supporting plate 252. Then, the bolt 28 is fixed to both of the supporting plates 25.sub.1 and 25.sub.2 by tightening the nut 35.

Annular sealing members 36 and 37 are interposed between the first sleeve 30 and the cylindrical member 29a at both ends, so as to prevent dust from entering the needle bearing 31. Similarly, an annular sealing member 38 is interposed between the second sleeve 32 at its outer 10 end and the cylindrical member 29b, and an annular sealing member 39 is interposed between the third sleeve 33 at its outer end and the cylindrical member 29b, so as to prevent dust from entering the ball bearing 34.

The operation of this preferred embodiment will now be described. As described above, the intermediate portions of the pair of cross pipes 23 and 24 extending laterally and vertically spaced from each other are welded to the downwardly extending portion 16c of the main pipe 16, and the pair of left and right supporting plates 25.sub.1 and 25.sub.2 are welded to both ends of each of the cross pipes 23 and 24. The swing arm 13 is pivotably supported by the bolt 28 extending between the supporting plates 25.sub.1 and 25.sub.2. In mounting the bolt 28 between the supporting plates 25.sub.1 and 25.sub.2 and shaft working for pivotal connection of the front ends of the swing arm 13 to the bolt 28, it is only necessary to preliminarily connect the supporting plates 25.sub.1 and 25.sub.2 through the cross pipes 23 and 24 to the single main pipe 16. After completing the shaft working for the connection of the swing arm 13, the down tubes 17.sub.1 and 17.sub.2 may be connected to the supporting plates 25.sub.1 and 25.sub.2. Accordingly, of all parts of the body frame 11, the main pipe 16, the cross pipes 23 and 24, the supporting sleeve 26, and the supporting plates 25.sub.1 and 25.sub.2 constitute a unit to be handled in a shaft working for the connection of the swing arm 13. Thus, the unit to be handled in the shaft working for the connection of the swing arm 13 can be made relatively small in size, and the operation for the shaft working for the connection of the swing arm can, therefore, be made easy.

Furthermore, the unit for pivotably supporting the swing arm 13 to the body frame 11 is composed of the single main pipe 16, the pair of cross pipes 23 and 24, the pair of supporting plates 25.sub.1 and 25.sub.2 , and the supporting sleeve 26. Accordingly, not only the number of parts can be made relatively small in size, but also a welding length can be reduced due to the reduction in the number of parts.

Further, since the supporting plates 25.sub.1 and 25.sub.2 are flat, they can be flexed so as to be closely fitted with the outer ends of the first and third sleeves 30 and 33 when the nut 35 is tightened to the bolt 28 in the condition where the front ends of the swing arm 13 are interposed between the supporting plates 25.sub.1 and 25.sub.2. Accordingly, this is advantageous in rigidity or in prevention of loosening of the nut 35. Moreover, rigidity balance can be adjusted only by adjusting the thickness of each plate.

The present invention may be applied to a three-wheeled automotive vehicle.

As described above, the present invention is characterized in that the body frame has a single main pipe comprising a rearwardly extending portion located over the engine and extending rearwardly from the head pipe, a bent portion extending from a rear end of the rearwardly extending portion, and a downwardly extending portion located behind the engine and extending downwardly from the bent portion. A pair of cross pipes extend laterally and are vertically spaced from each other and connected at their intermediate portions to the downwardly extending portion of the main pipe. A pair of supporting plates are located so as to be interpose therebetween the downwardly extending portion of the main pipe which are connected to both ends of each of the cross pipes. The front end of the swing arm is pivotably supported to a pivot shaft located between the cross pipes and extending between the supporting plates. Accordingly, a portion of the body frame to be handled in the shaft working for the connection of the swing arm can be composed of a minimum number of parts, that is, the main pipe, the pair of cross pipes, and the pair of supporting plates. Further, this portion to be handled in shaft working for the connection of the swing arm can be made relatively small in size. As a result, the operation for the shaft working for the connection of the swing arm can be made easy, and a welding length can be reduced due to the reduction in number of parts.

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 following claims.