JPH0587432B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field The present invention relates to a frame structure for a straddle-type vehicle including a motorcycle, a three-wheeled vehicle, and the like.

Background Art The frame structure shown in Fig. 4 is, for example,
It is disclosed in Japanese Patent No. 17768, and as shown in the figure, a head pipe 1 bearing a front fork is shown.
01 has a pair of left and right main pipes 102 connected at the front end. The main pipe 102 is
A pivot portion 105 for pivotally supporting the front end of a swing arm 104 that pivotally supports a rear wheel 103 is provided at the rear end, and is integrally formed over the entire length.

The above frame structure includes a head pipe 101,
It is assembled by joining the main pipe 102 and other members such as stays to each other by welding, but it is difficult to completely prevent the generation of residual stress due to welding, and the so-called caster angle and Errors due to distortion may occur in the center-to-center distance between the center of the head pipe 101 and the pivot portion 105, which is an element of frame rigidity. In this case, after the assembly of the frame structure is completed, it is necessary to use special equipment to remove distortion from the frame structure as a whole, and such distortion removal work requires a long time and skill, leading to an increase in frame manufacturing costs. .

Summary of the Invention [Object of the Invention] The present invention has been made in view of the above-mentioned points, and its purpose is to contribute to facilitating accuracy control of frame structure, and to provide a lightweight and highly rigid structure. The purpose is to provide a frame structure.

[Structure of the Invention] The frame structure of the straddle type vehicle according to the present invention has a front end connected to an upper part of a head pipe that rotatably supports a front fork, and a pair of left and right first frames extending rearward and downward. a frame member, and a pivot portion that is connected to the rear end portion of the first frame member by butt welding and has the same cross-sectional shape, extends downward, and pivotally supports the front end portion of a swing arm that pivotally supports the rear wheel. a pair of left and right second frame members having: a seat support whose front end portions are joined by butt welding to the upper surface of the second frame member near the joint joined by the butt welding and extending rearward and upward; The apparatus is characterized in that it has a frame, and a connecting member that connects at least the first frame member in the vicinity of the joint portion joined by the butt welding and the lower part of the head pipe.

[Operation of the invention] In the frame structure having such a configuration, since the butt welded portions of the first frame member and the second frame have the same cross-sectional shape, the directionality of strain in the welded portion is eliminated, and the It acts to suppress local stress concentration.

In addition, by providing a connecting member that connects the lower part of the head pipe and the vicinity of the joint made by butt welding, a force is applied to push the joint towards the rear of the vehicle, and a seat support is connected to the upper surface of the second frame member near the joint. By applying a force that pushes the joints toward the front of the vehicle through the frame, it is possible to cancel the force acting in the longitudinal direction of the vehicle at the joints, thereby reducing the stress generated in the joints and causing fatigue failure of the joints. etc. can be prevented.

Embodiments Hereinafter, a motorcycle including a frame structure as an embodiment of the present invention will be described with reference to the accompanying drawings.

FIG. 1 shows a motorcycle equipped with an aluminum double cradle type frame structure 34 as an embodiment of the present invention. FIGS. 2-3b also show details of the frame structure 34. FIG.

As shown in FIG. 1, the seat 4 and the fuel tank 5 are supported by a frame structure 34 together with an engine 6 disposed at the lower center of the vehicle body.

A head pipe 35 made of aluminum alloy or steel is provided in front of the frame structure 34, and includes a steering mechanism 9 and a front fork 1.
It is connected to the front wheel 11 via 0. Further, the rear portion of the frame structure 34 is connected to the rear wheel 12 via a swing arm, which will be described later.

In this embodiment, a head pipe 35 rotatably supports the front fork 10, and main pipes 36 serve as a pair of left and right first frame members that support the upper and lower parts of the head pipe 35, respectively.
(the part indicated by dimension Mc in Fig. 2), the sub-main pipe 37, and the left and right main pipes 3
Before assembling the entire frame structure, the stay 38 is interposed between the head pipe 35 and the sub-main pipe 37 and has both ends welded to the main pipe 36 together with the sub-main pipe 37, and the stay 39 provided between the head pipe 35 and the sub-main pipe 37. It is manufactured in advance as a first block. Note that the main pipe 36 forms the upper part of the entire frame structure. The stay 38 is provided with a pair of left and right engine hangers 36a, and the main pipe 36 supports an engine (not shown) via the stay 38. Further, the machining of the head pipe 35 is performed when the assembly of the first block is completed. In addition, the first
As for the main pipe 36 as a frame member, the head pipe 35 is connected to the front end of the main pipe 36 as described above.
It connects to the ridge and extends rearward and downward.

A pair of left and right down tubes A40 whose upper ends are welded near the front end of the sub-main pipe 37
(The portion indicated by dimension Dc in FIG. 2) extends obliquely downward. However, this down tube A40 is not connected to the stay 39.
Further, both down tubes A are also provided with engine hangers. Left and right down tube A4
0 is prefabricated as a second block together with a cross stay 41 (shown in FIG. 3b) interposed between both down tubes A.

A pair of left and right down tubes B44 (dimensions shown in FIG.
The part indicated by Dd) is the down tube A4
Together with 0, it constitutes the entire down tube that forms the lower part of the entire frame structure (however,
Only the left side of the mating portion 42 and inner pipe 43 are shown). The joining portion 42 divides the entire down tube into a down tube A40 and a down tube B44.

Further, the down tubes A40 and B44 are formed in a straight line at the portion where the mating portion 42 is provided. The joining portion 42 is inclined with respect to the direction of extension of both down tubes A40 and B44, and the welding length at the joining portion is relatively large. Further, the inner pipe 43 is connected to both down tubes A40 and B44 by plug welding. Further, plug welding of the inner pipe is performed prior to butt welding of the mating portion 42. A gusset 44b having a pivot portion 44a for pivotally supporting the front end of the swing arm 21 that pivotally supports the rear wheel 12 is fixed to the front surface of the left and right down tubes B44. Further, a stay 45 for attaching the step holder 22 is fixed to the rear surface of the down tube B44.

The left and right down tubes B44 are manufactured in advance as a third block together with a cross member 46 interposed between the two down tubes B.

The upper end of the down tube B44 is the mating part 49
It is fixed to the rear end of the main pipe 36 as the first frame member by butt welding. The stay 38 is also welded to the upper end of the down tube B44 around the joint portion,
By doing this, the state of connection between the main pipe 36 and the down tube B44 at the joint portion 49 is strengthened. Note that welding between the stay 38 and the down tube B44 is performed prior to butt welding of the mating portion 49.

By the way, in the explanation so far, the main pipe 36 has been referred to as the first frame member, but on the other hand, the down tube B44 described above has been referred to as the first frame member.
The gusset 44 includes the upper half portion (the portion indicated by dimension DB in Fig. 2) and the pivot portion 44a.
The combined body with b is collectively referred to as a second frame member.
That is, this second frame member has a pivot portion 44a that pivotally supports the swing arm 21, and
Its front end is joined to the rear end of the main pipe 36, which is a frame member, and extends downward as a whole.

As shown in FIG. 3b, the left and right down tubes A40 are bent so that they become closer to each other as they go downward, and the left and right down tubes
The distance between the pivot portions 44a of the frame members in the left-right direction of the vehicle is narrow and approximately equal to the width between the lower ends of both down tubes A40. Therefore, the distance in the left-right direction of the vehicle between the pair of left and right pivot portions 44a (only the left side is shown in the figure) is the distance between the engine support portion and each of the pair of left and right main pipes 36 as the first frame member. The distance between the two engine hangers 36a is smaller than the distance between the two engine hangers 36a that are fixed to each other. In other words, the width around the step holder described above is smaller than the distance between the engine support parts of the left and right main pipes 36.

As mentioned above, since the width around the step holder located at the bottom of the vehicle body is smaller than the distance between the engine support parts of the main pipe 36, the vehicle body can be slimmed down and the driver can enjoy more freedom in riding posture. This increases the steering angle and provides a good riding feeling, as well as improving maneuverability of the vehicle body and increasing the bank angle. Furthermore, as for the pair of left and right main pipes 36 that act as engine support parts without being involved in riding feeling, the separation distance and cross-sectional dimensions of these can be increased, so that the desired rigidity for engine support can be achieved. It is guaranteed.

In addition, as mentioned above, the second pair of left and right
Both down tubes B4 that form part of the frame member
4 are connected to each other by a cross member 46 interposed between them. This configuration increases the rigidity of the second frame member including both down tubes B44, and is effective against torsional stress applied to the pivot portion 44a. Also,
By providing this cross member 46, the rigidity of the joint portion 49, which is the joint portion between the first frame member and the second frame member, is also increased.

On the other hand, a seat rail 50 as a seat support frame is provided at the upper end of both the left and right down tubes B44.
The front end of the seat rail is fixed to the seat rail, and the seat rail extends diagonally rearward. seat rail 50
A seat supporting auxiliary frame 51 and a sub-rear stay 5 are provided between the approximately middle part of the down tube B44 and the down tube B44.
2 is provided.

As is particularly clear in FIG. 3a, cross members 53a and 53b are horizontally suspended between the left and right seat rails 50 and the seat support auxiliary frame 51. Further, a cross pipe 54 is horizontally suspended between the respective rear end portions of both seat rails 50.

The seat rail 50, seat support auxiliary frame 51, and sub-rear stay 52 are assembled in advance as a fourth block.

In addition, by providing the above-mentioned seat support auxiliary frame 51 and cross members 53a and 53b, the down tube B44, which forms part of the second frame member including the swing arm pivot part 44a, and the seat support frame are The stiffness of the interconnection with the seat rail 50 is increased.
In addition, these seat support auxiliary frames 51, cross members 53a and 53b, and seat rails 5
0, the rigidity of the pair of left and right second frame members themselves is increased.

When assembling the entire frame structure 34,
The first to fourth blocks are sequentially welded, and finally the mating parts 42 and 49 are welded.
By welding the joining parts 42 and 49 at the final stage of the frame structure assembly work in this way, it is possible to absorb manufacturing errors caused by distortions that occur when assembling the frame structure by welding, especially as shown by θ in the figure. The caster angle and the center-to-center distance between the center of rotation of the front fork and the pivot portion 44a, indicated by L, are precisely dimensioned.

It goes without saying that various other embodiments can be considered as a method for welding the joining parts 42 and 49.

As mentioned above, in the frame structure according to the present invention, since a method is adopted in which the frame structure is manufactured separately into several block parts divided by the above-mentioned joint parts and others before being assembled, each part of the frame structure Compared to the conventional method in which all parts are manufactured and managed separately, precision control of the frame structure and inventory control of parts are simplified.

Further, since the head pipe can be machined at the time of manufacturing the block portion, the object to be machined can be relatively small, making the machining process easy.

Effects of the Invention As detailed above, in the frame structure for a straddle-type vehicle according to the present invention, the frame connecting the head pipe that supports the front fork and the pivot part that pivotally supports the swing arm is connected to the frame structure that rotates the front fork. A pair of left and right first frame members whose front ends are joined to the upper part of the head pipe that is freely supported on the shaft and extend rearward and downward, and the rear ends of the first frame members are butt-welded to each other with the same cross-sectional shape. A pair of left and right second frame members are connected to each other and have a pivot portion that extends downward and pivotally supports the front end of a swing arm that pivotally supports the rear wheel.

That is, since the butt welded portions of the first frame member and the second frame member have the same cross-sectional shape, the directionality of strain in the welded portion is eliminated, and local stress concentration after welding can be suppressed. Therefore, even if tensile, compressive, bending, or other loads are repeatedly applied to such a joint, fatigue failure of the joint can be prevented by improving the fatigue limit.

Furthermore, the method of connecting the above-mentioned joint portions is not such that the second frame member is superimposed on the outer surface of the first frame member and welded, or that the two frame members are welded together via another member, but the ends of both members are directly connected. Since it is a butt welding method, it is possible to reduce the width of the vehicle and thereby improve knee grip characteristics.

Further, a seat support frame extending in the longitudinal direction of the vehicle across the joint between the first frame member and the second frame member and a connecting member connected to the lower part of the head pipe are both connected near the joint. As a result, the rigidity against bending loads etc. applied to such joints can be increased, and it is possible to prevent vibrations (chatter) of the vehicle body that occur due to the low rigidity frame, especially when braking the vehicle where a large load is applied.

To be more specific, for example, when a vehicle running at high speed is suddenly braked, a load is applied via the front wheels that bends the lower part of the head pipe toward the rear of the vehicle, while an inertial load of the passenger is applied to the seat support member. This acts to push the joint portion forward of the vehicle, and the joint portion between the first frame member and the second frame member is placed in a severe stress situation.

Therefore, by providing a connecting member that connects the lower part of the head pipe and the vicinity of the joint, a force is applied to push the joint towards the rear of the vehicle, and the seat support frame is connected to the upper surface of the second frame member near the joint. By applying a force that pushes the joint toward the front of the vehicle, it is possible to cancel the force acting on the joint in the longitudinal direction of the vehicle, thereby reducing the stress generated in the joint and preventing fatigue failure of the joint. be able to.

Further, the front end of the seat support frame and the rear end of the connecting member, which are connected near the joint between the first frame member and the second frame member, are connected to the second frame member and the first frame member, respectively. This makes it possible to take a procedure such as joining the first frame member (first block) to which the connecting member has been joined in advance and the second frame member to which the seat support frame has been joined in advance. Since another welding process is performed in the vicinity of the joint after welding and joining the second frame member to the second frame member, it is possible to prevent the occurrence of distortion due to the influence of heat at the joint.

[Brief explanation of the drawing]

Fig. 1 is a side view of a motorcycle equipped with a frame structure as an embodiment of the present invention, Fig. 2, and Fig. 3a.
and b are a side view, a plan view, and a front view of the frame structure shown in FIG. 1, respectively, and FIG. 4 is a side view of a motorcycle including a conventional frame structure. Explanation of symbols of main parts, 4... sheet, 5...
Fuel tank, 6... Engine, 34... Frame structure, 35... Head pipe, 36... Main pipe, 37... Sub main pipe (connecting member),
44...Down tube B, 44a...Pivot part, 46, 53a, 53b...Cross member, 5
0... Seat rail, 51... Seat support auxiliary frame.

Claims (1)

[Scope of Claims] 1. A pair of left and right first frame members whose front end portions are connected to an upper portion of a head pipe that rotatably supports a front fork and extend rearward and downward, each of the first frame members a pair of left and right second frame members each having a pivot part connected to the rear end part by butt welding with the same cross-sectional shape, extending downward, and pivotally supporting the front end part of a swing arm that pivotally supports the rear wheel; , a seat support frame whose front end portion is joined to the upper surface of the second frame member by butt welding in the vicinity of the joint joined by the butt welding and extends rearward and upward; and the joint joined by the butt welding. A frame structure for a straddle-type vehicle, comprising a connecting member that connects at least the first frame member near the head pipe and a lower part of the head pipe.