Frame for vehicle

A frame for a vehicle includes a first frame member having a square tube-like joint end portion and a second frame member having a square tube-like joint end portion. The joint end portion of the first frame member and the joint end portion of the second frame member are butt-welded to each other. The joint end portions of the first and second frame members each has circumferentially continuous first-fourth edges and the first-fourth edges are inclined when the joint end portions are viewed radially in any direction.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a frame used in a vehicle, such as a motorcycle, and particularly to the structure of a welded joint for joining two frame members.

2. Description of Related Art

A frame for a motorcycle supports main components such as an engine, a front fork and a rear arm, and has the function of receiving impulsive loads or fatigue failure loads transmitted from the front fork and the rear arm during running.

Since this kind of frame requires high strength and rigidity as well as light weight, a conventional frame includes a plurality of rectangular tube-like frame members which are welded to each other and assembled. In the frame of this type, joint end portions of the plurality of frames are cut obliquely to secure the welding length between the joint end portions, so as to ensure the strength of the welded joint portions.

In the frame disclosed above, the joint end portion of the frame member is cut obliquely when the frame is viewed from the side. Therefore, when the left and right side edges of the joint end portion are inclined to the axis of the frame member, the overall length of the side edges becomes larger compared with when these side edges cross the axis of the frame member at right angles.

However, with the conventional frame, there is nothing mentioned regarding the shapes of the front and rear ends of the frame member. Therefore, the welding length of the welded joint portion is earned only by the left and right side edge portions and thus the welding length of the welded joint portion is hardly sufficient.

An advantage of the present invention is to provide a frame for a vehicle capable of securing a sufficient welding length between joint end portions without complicating the shapes of the joint end portions of the first and second frame members.

SUMMARY OF THE INVENTION

In order to achieve the foregoing advantage, the frame for a vehicle according to one embodiment of this invention includes a first frame member having a square tube-like joint end portion and a second frame member having a square tube-like joint end portion. The joint end portion of the first frame member and the joint end portion of the second frame member are butt-welded to each other. The joint end portions of the first and second frame members have circumferentially continuous first-fourth edges, respectively, and the first-fourth edges are inclined when the joint end portions are viewed radially in any direction.

According to an embodiment of the present invention, the circumferential length of the joint end portion can be increased without complicating the shapes of the first-fourth edges. Therefore, a sufficient welding length can be secured between the joint end portions, improving the welding strength of the first and second frame members.

DETAILED DESCRIPTION OF THE INVENTION

Now, a first embodiment of the present invention will be described with reference toFIG. 1throughFIG. 10in which the present invention is applied to a motorcycle.

FIG. 1shows a motorcycle1, for example, for motocross races. The motorcycle1is provided with a frame2of a cradle type. The frame2supports a front fork3; a rear arm4; a water-cooled, four-stroke, single-cylinder engine5; a fuel tank6; and a seat7.

The front fork3is controlled by a bar handle8for steering and supports a front wheel9. The rear arm4extends rearward from the frame2and supports, at its rear end, a rear wheel10. The engine5is designed to drive the rear wheel10and has a drive sprocket12at the rear end of a crankcase11. A chain14is stretched between the drive sprocket12and a driven sprocket13of the rear wheel10.

The fuel tank6is located directly above the engine5. The seat7extends rearward of the fuel tank6approximately horizontally from the upper surface of the fuel tank6.

As shown inFIG. 1throughFIG. 3, the frame2is provided with a first frame section16, a second frame section17, left and right seat rails18and left and right seat pillar tubes19.

The first frame section16is a cast product of an aluminum alloy and provided with a steering head pipe20and a gusset portion21. The steering head pipe20is located at the forward end of the frame2and supports the front fork3.

The gusset portion21extends obliquely downward toward the rear from the steering head pipe20and is in a hollow, box-like shape elongated in the direction of height of the frame2. The gusset portion21has a connecting portion22protruding obliquely downward toward the rear, and one first down tube23protruding downward.

The connecting portion22is in the shape of a square box expanded laterally of the vehicle toward the rear, and formed, at the rear end, with an opening24which is open rearward. The first down tube23is in the shape of a rectangular tube of a square cross-section and has, at its lower ends, a pair of forked connecting arm portions25a,25b. The connecting arm portions25a,25bprotrude downward along the first down tube23and disposed parallel to each other with a space in the lateral direction of the vehicle.

The second frame section17is provided with a pair of rear arm brackets27a,27b, a cross member28and a rear cushion bracket29. The rear arm brackets27a,27bare formed from forged products of aluminum alloy. The rear arm brackets27a,27bstand behind the first down tube27in the direction of the height of the frame2and are disposed parallel to and separate from each other laterally of the vehicle. The rear arm brackets27a,27bhave bosses30, respectively. The forward ends of the rear arm4are placed between the bosses30and supported by the bosses30through a pivot shaft31.

The upper edges of the rear arm brackets27a,27bextend toward the connecting portion22of the first frame section16. The upper ends of the rear arm brackets27a,27bare fitted in an opening24of the connecting portion22and welded to the edge of the opening24.

The cross member28is formed from extruded aluminum alloy into the shape of a rectangular tube. The cross member28connects the rear arm brackets27a,27bat the lower ends. The cross member28is located below the rear arm4, and a link mechanism32extends across the space between the rear end of the cross member28and the rear arm4.

The rear cushion bracket29is a cast product of aluminum alloy and in the shape of a rectangular tube. The rear cushion bracket29connects the upper parts of the rear arm brackets27a,27b. One hydraulic shock absorber33extends between the rear cushion bracket29and the link mechanism32connected to the rear arm4.

As shown inFIG. 1, the rear cushion bracket29supports the forward end of the seat rail18. The seat rail18extends rearward from the rear cushion bracket29and supports the rear half of the seat7. The seat pillar tube19extends between the rear half of the seat rail18and the lower parts of the rear arm brackets27a,27band supports the rear end of the seat rail18.

As shown inFIG. 2throughFIG. 4, the connecting arm portions25a,25bof the first down tube23and the lower ends of the rear arm brackets27a,27bare connected through left and right second down tubes35a,35b. The second down tubes35a,35bare formed from extruded aluminum alloy, for example. The forward ends of the second down tubes35a,35bare welded to the connecting arm portions25a,25bof the first down tube23. The rear ends of the second down tubes35a,35bare welded to the lower ends of the rear arm brackets27a,27b. Therefore, the second down tubes35a,35bextend longitudinally of the frame2and are disposed separate from each other laterally of the vehicle.

The first down tube23, second down tubes35a,35band rear arm brackets27a,27bsupport the crankcase11of the engine5so as to be enclosed.

Specifically, as shown inFIG. 2, first engine brackets36are attached to the connecting arm portions25a,25bof the first down tube23, respectively. The first engine brackets36support the forward end of the crankcase11. Second engine brackets37are attached to the second down tubes35a,35bin the middle. The second engine brackets37support the lower end of the crankcase11.

The rear end of the crankcase11is placed between the bosses30of the rear arm brackets27a,27band is supported by the bosses30through a pivot31. Therefore, the first down tube23and the second down tubes35a,35brun around the crankcase11of the engine5from the front to the bottom thereof.

In the frame2as described above, a device is made to increase the joint strength between the connecting arm portions25a,25bof the first down tube23and the second down tubes35a,35b. Now, the construction of welded joints38for joining the connecting arm portions25a,25band the second down tubes35a,35bwill be described below by explaining, as an example, a joint portion between the left connecting arm portion25aand the left second down tube35a.

The connecting arm portion25aof the first down tube23is a component corresponding to the first frame member of this invention, and has a rectangular tube-like shape with a front wall40a, a rear wall40b, and left and right side walls40c,40das shown inFIG. 5andFIG. 6. The connecting arm portion25ais provided, at its lower end, with a joint end portion41and a projection42. The joint end portion41is in a square shape defined by first-fourth edges43a-43d, respectively, and directed downward of the first down tube23.

The first edge43aof the joint end portion41is located at the lower end of the front wall40aand extends linearly in the lateral direction of the connecting arm portion25a. The second edge43bof the joint end portion41is located at the lower end of the rear wall40band extends linearly in the lateral direction of the connecting arm portion25a. Therefore, the first edge43aand the second edge43bare spaced from each other in the longitudinal direction of the connecting arm portion25a.

The third edge43cof the joint end portion41is located at the lower end of the left side wall40cand extends linearly in the longitudinal direction of the connecting arm portion25a. The fourth edge43dof the joint end portion41is located at the lower end of the right side wall40dand extends linearly in the longitudinal direction of the connecting arm portion25a. Therefore, the third edge43cand the fourth edge43dare spaced from each other in the lateral direction of the connecting arm portion25a. In other words, the first edge43aand the second edge43b, and the third edge43cand the fourth edge43dface each other in the radial direction of the connecting arm portion25a, respectively.

As shown inFIG. 4andFIG. 5, the first and second edges43aand43b, respectively, are inclined upward toward the outer side (left side) in the lateral direction of the connecting arm portion25a. Likewise, the third and fourth edges43cand43d, respectively, are inclined upward from the front toward the rear of the connecting arm portion25a. Further, the first-fourth edges43a-43d, respectively, are located on the same plane radially of the connecting arm portion25a.

As a result, the square joint end portion41defined by the first-fourth edges43a-43d, respectively, is cut obliquely so as to be directed leftward and rearward of the frame2relative to a plane perpendicular to the axis01of the connecting arm portion25apassing through the center of the joint end portion41. Therefore, the first-fourth edges43a-43d, respectively, are inclined when the joint end portion41is viewed in any direction radially of the connecting arm portion25a.

The projection42protrudes downward from a region surrounded by the first-fourth edges43a-43d, respectively, of the joint end portion41. This projection42is in a square tube-like shape coaxial to the joint end portion41.

On the other hand, the second down tube35ais a component corresponding to the second frame member of the present invention and has a rectangular tube-like shape with first-fourth circumferential walls45a-45d, respectively, as shown inFIG. 9. The second down tube35ais provided, at the forward end, with an upward joint end portion46. The joint end portion46is in a square shape defined by first-fourth edges47a-47d, respectively, and configured such that the projection42of the foregoing joint end portion41is inserted therein.

The first edge47aof the joint end portion46is located at the forward end of the first circumferential wall45aand extends linearly in the lateral direction of the second down tube35a. The second edge47bof the joint end portion46is located at the forward end of the second circumferential wall45band extends linearly in the lateral direction of the second down tube35a. Therefore, the first edge47aand the second edge47bare spaced from each other in the longitudinal direction of the second down tube35a.

The third edge47cof the joint end portion46is located at the forward end of the third circumferential wall45cand extends linearly in the longitudinal direction of the second down tube35a. The fourth edge47dof the joint end portion46is located at the forward end of the fourth circumferential wall45dand extends linearly in the longitudinal direction of the second down tube35a. Therefore, the third edge47cand the fourth edge47dare spaced from each other in the lateral direction of the second down tube35a. In other words, the first edge47aand the second edge47b, and the third edge47cand the fourth edge47dface each other in the radial direction of the second down tube35a, respectively.

As shown inFIG. 4andFIG. 8, the first and second edges47aand47b, respectively, are inclined upwardly toward the outer side (left side) in the lateral direction of the second down tube35a. Likewise, the third and fourth edges47cand47d, respectively, are inclined upward toward the rear of the second down tube35a. Further, the first-fourth edges47a-47d, respectively, are located on the same plane radially of the second down tube35a.

As a result, the square joint end portion46defined by the first-fourth edges47a-47d, respectively, is cut obliquely so as to be directed rightward and forward of the frame2relative to a plane perpendicular to the axis02of the second down tube35apassing through the center of the joint end portion46. Therefore, the first-fourth edges47a-47d, respectively, are inclined when the joint end portion46is viewed in any direction radially of the second down tube35a.

In the condition in which the projection42of the connecting arm portion25ais inserted in the joint end portion46of the second down tube35, the first-fourth edges43a-43d, respectively, of the joint end portion41and the first-fourth edges47a-47d, respectively, of the joint end portion46face each other so as to be parallel, respectively, and small clearances are formed to absorb dimensional errors between them.

As shown inFIG. 10, the connecting arm portion25aand the second down tube35aare welded throughout the circumference, with their joint end portions41,46butted against each other. As a result, a welding bead48is formed between the joint end portions41,46, and the connecting arm portion25aand the second down tube35aare joined integrally. In this case, the projection42of the connecting arm portion25aacts as a backing strip for closing the clearance from the inner side of the second down tube35a.

According to the first embodiment of the present invention as described above, the first-fourth edges43a-43d, respectively, defining the joint end portion41of the connecting arm portion25aare inclined when the joint end portion41is viewed in any direction radially of the connecting arm portion25a. Likewise, the first-fourth edges47a-47d, respectively, defining the joint end portion46of the second down tube35aare inclined when the joint end portion46is viewed in any direction radially of the second down tube35a.

Therefore, the first-fourth edges43a-43d, respectively, of the joint end portion41become longer compared with when these first-fourth edges43a-43d, respectively, are located on a plane perpendicular to the axis01. Likewise, the first-fourth edges47a-47d, respectively, of the joint end portion46become longer compared with when these first-fourth edges47a-47d, respectively, are located on a plane perpendicular to the axis02.

As a result, the circumferential lengths of the joint end portions41,46are increased and the welding length between the joint end portions41,46and thus the length of the welding bead48can be sufficiently secured. This improves the strength of the welded joints38for joining the first down tube23and the second down tubes35a,35b.

In addition, the first-fourth edges43a-43d, respectively, of the joint end portion41and the first-fourth edges47a-47d, respectively, of the joint end portion46are located on the same planes, respectively. Therefore, the joint end portions41,46each have a simple shape with no irregularities, and the welding length between the joint end portions41,46can be secured without complicating the shapes of the joint end portions41,46.

Further, all of the first-fourth edges43a-43d, respectively, of the joint end portion41and the first-fourth edges47a-47d, respectively, of the joint end portion46extend straight. Therefore, when welding work is performed using, for example, a welding robot, the welding robot needs to be moved only circumferentially of the connecting arm portion25aand the second down tubes35a,35b. This is convenient in promoting automation of the welding work and facilitating control relating to the movement of the welding robot.

Furthermore, the joint end portion41of the connecting arm portion25ais cut obliquely so as to be directed outward in the lateral direction of the vehicle relative to the connecting arm portion25a. Therefore, when the second down tube35ais connected to the connecting arm portion25a, the joint end portion46of the second down tube35acan be brought in abutment against the joint end portion41of the connecting arm portion25afrom the left side in the lateral direction of the vehicle. As a result, the working efficiency in assembling the frame2is improved

This invention is not limited to the foregoing first embodiment, but a second embodiment of this invention is shown inFIG. 11.

In the second embodiment, there is no component corresponding to the backing strip in the joint end portion41of the connecting arm portion25a. The joint end portion41of the connecting arm portion25aand the joint end portion46of the second down tube35aare simply in abutment against each other.

In this arrangement, four edges of the joint end portions41,46are also inclined, so that a sufficient welding length between the joint end portions41,46can be secured.

This invention is not limited to the joint portion of the first down tube and the second down tube. For example, when one rectangular tube-like frame member passing above the engine is divided longitudinally, this invention may be applied to the portion at which the divided ends are welded to each other.

Further, this invention is not limited to a motorcycle, but may also be practiced, for example, in an All Terrain Vehicle (ATV), for running rough grounds, with three or four wheels.