SWING

Abstract

Swing arm (8), comprising: - a hollow body (52) with a pivot hole (51) accommodating a pivot shaft (25); - a suspension fixing part (53) which is provided in the hollow body (52) and connected to an end section of a suspension unit (35); - a pair of arms (56) extending from the hollow body (52) and supporting the ends of a wheel axle (55), wherein - the hollow body (52) and the spring fixing part (53) are integrally formed workpieces created by casting; - each of the paired arms (56) has an outer part (61) with an open cross-section and an inner part (62) with an open cross-section; - the outer part (61) and the inner part (62) of each arm (56) are welded together at their respective open end sections (63, 64); and - the hollow body (52) has first opening sections (81) which are welded to a corresponding edge section (61a) of the outer part (61) of the arms (56), second opening sections (82) which are welded to a corresponding outer surface (66) of the inner part (62) of the arms (56), and reinforcing support struts (83) which subdivide the first opening sections (81) and the second opening sections (82), are welded to a corresponding front edge section of the inner part (62) of the arms (56), reinforce the connection between the hollow body (52) and the arms (56), and are installed between the top and bottom of the hollow body (52), wherein the interior of the hollow body (52) is formed without a transverse reinforcing wall.

Description

BACKGROUND OF THE INVENTIONField of the invention

[0001] The present invention relates to a swing arm, Description of the state of the art

[0002] In a vehicle such as a motorcycle, there is a swingarm (swing arm) comprising a pair of right and left arms for pivotally supporting a rear wheel. A body portion is provided between the front ends of the respective arm portions, connecting the paired arm portions. At the front end portion of the body portion, there is a joint portion that pivotally mounts the swingarm to the vehicle frame (see, for example, JP H05-105 171 A).

[0003] JP H02-175 482 A shows a motorcycle rear swingarm in which a cast inner part is press-fitted into a cast outer part. JP 2013-47 036 A shows a swingarm with two hollow cast parts with a square cross-section, the inner sections of which are welded to a connecting part near the pivot axis.

[0004] JP H05-105 171 A shows a similar swing arm in which the connecting part between the hollow lateral arms is extended and forms a hollow axle at its end on which the swing arm is suspended. DISCLOSURE OF THE INVENTION

[0005] Each arm of a conventional swingarm includes an outer part with an open cross-section and an inner part joined to the outer part and having an open cross-section. The front end portion of the outer part of the right arm and the front end portion of the outer part of the left arm cover the right and left opening portions of the body portion. The front end portions of the respective inner parts of the right and left arms are in contact with the rear wall of the body portion. The front end portion of each outer part and the front end portion of each inner part are fixed to the body portion by welding.

[0006] The body section is an extrusion-molded part. The interior of the body section contains a reinforcement wall that extends in the width direction.

[0007] However, the reinforcement wall crossing the interior of the body section increases the weight of the swingarm.

[0008] In order to solve the problems described above, it is an object of the invention to provide a swingarm which ensures rigidity and is lighter than the conventional swingarm which is equipped with a reinforcing band crossing the interior of the body.

[0009] To achieve the above object, one aspect of the present invention provides a swing arm having the features of claim 1.

[0010] A preferred embodiment of the above aspect is set out in claim 2. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] In the accompanying drawings: Fig. 1 is a left-side view of a motorcycle in which the swing arm according to an embodiment of the invention is used; Fig. 2 is a plan view of the rocker according to the embodiment of the invention; Fig. 3 is a left-side view of the swing arm according to the embodiment of the invention; Fig. 4 is a cross-sectional plan view of the rocker according to the embodiment of the invention; Fig. 5 an enlarged view of part of the Fig. 4; Fig. 6 is a perspective view of the swing arm according to the embodiment of the invention, with the left arm omitted; and Fig. 7 is a partially exploded perspective view of the arm of the swing arm according to the embodiment of the invention. DETAILED DESCRIPTION

[0012] In the following, an embodiment of a swing arm according to the present invention is described with reference to Fig. 1 to 7 explained.

[0013] Fig. 1 is a left side view of a motorcycle to which the swing arm according to the embodiment of the invention is applied.

[0014] In the present embodiment, directions of the engine 1 such as front, rear, top, bottom, right, and left refer to the position of a rider riding the motorcycle 1.

[0015] As in Fig. 1, the motorcycle 1 according to the embodiment of the invention is, for example, an off-road motorcycle such as a multi-purpose bike or a motocross bike, which is used for riding on uneven ground, irregular ground, and rough terrain. The motorcycle 1 includes a vehicle frame 2, a front wheel 5, a steering mechanism 6, a rear wheel 7, a swingarm 8, an engine 9, and an engine control module 11. The vehicle frame 2 extends in the longitudinal direction of the motorcycle 1. The front wheel 5 is located in front of the vehicle frame 2. The steering mechanism 6 is located in front of the vehicle frame 2 and rotatably supports the front wheel 5. The rear wheel 7 is located behind the vehicle frame 2. The swingarm 8 extends rearward from the vehicle frame 2 to rotatably support the rear wheel 7. The engine 9 is mounted in the lower center region of the vehicle frame 2. The engine control module 11 controls all operations of the engine 9.

[0016] The vehicle frame 2 is of the so-called cradle type. The vehicle frame 2 includes a steering head 13, a pair of right and left main frames 15, a pair of right and left articulated frames 16, a down tube 17, a connecting member 18, a pair of right and left down beams 19, a pair of right and left bridge members 21, and a rear frame 22. The steering head 13 is located at the front upper end portion. The paired right and left main frames 15 are connected to the steering head 13. The pair of right and left articulated frames 16 are connected to the respective rear end portions of the right and left main frames 15. The down tube 17 is connected to the steering head 13, and the connecting member 18 is connected to the down tube 17. The pair of right and left down tubes 19 are connected to the respective branched ends of the connecting member 18.The right bridge part 21 bridges the area between the right main frame 15 and the down tube 17, and the left bridge part 21 bridges the area between the left main frame 15 and the down tube 17. The rear frame 22 is connected to the pair of right and left articulated frames 16.

[0017] Each of the main frames 15 extends obliquely rearward and downward from the front end portion connected to the steering head 13. Each of the articulated frames 16 hangs downward from the front end portion connected to the rear end portions of the right and left main frames 15. The down tube 17 extends downward from the end portion connected to the steering head 13. The connecting member 18 bifurcates, i.e., branches to the right and left portions of the motorcycle 1. The respective down tubes 19 are connected to the branch end portions of the connecting member 18. Each of the down tubes 19 extends downward from the connecting end with the connecting member 18. The respective down tubes 19 are bent rearward at their central portion to protect the lower part of the engine 9, and the down tubes are connected to the lower end portions of the respective articulated frames 16.The rear frame 22 extends from the connecting end with the articulated frame 16 to the rear.

[0018] The steering head 13 is the center of rotation of the steering mechanism 6. The steering head 13 supports the steering mechanism 6 on the vehicle frame 2.

[0019] The right and left main frames 15 also serve as tank rails. The right and left main frames 15 support a fuel tank 23 above the main frames 15. The right and left main frames 15 form a suspension for the engine 9 below the fuel tank 23.

[0020] The right and left articulated frames 16 carry a pivot shaft 25, which is the center of rotation of the swing arm 8.

[0021] The rear frame 22 includes a pair of right and left seat rails 26 and a pair of right and left seat support tubes 27. The right and left seat rails 26 extend obliquely rearward and upward from the rear end portions of the right and left main frames 15 and the respective upper portions of the right and left articulated frames 16. The pair of right and left seat support tubes 27 extend upward and rearward from the rear sides of the respective center portions of the articulated frames 16 and are connected to the respective rear portions of the seat rail 26. The seat rails 26 support a seat 28 and a rear fender 29 which extends rearward from the seat 28 and covers the upper part of the rear wheel 7.

[0022] The steering mechanism 6 includes a fork 31 consisting of left and right fork portions, a front fender 32, and a handlebar 33 in the form of handgrips. The upper portion of the front fork 31 rotatably supports the front wheel 5. The front fender 32 covers the area above the front wheel 5. A suspension mechanism (not shown) is installed in each portion of the front fork 31. A rider can steer the front wheel 5 right and left by grasping the handgrips 33. The handlebar 33 on the right side of the motorcycle 1 supports a throttle grip 33a.

[0023] The swing arm 8 is pivotally mounted on the vehicle frame 2 and rotatably supports the rear wheel 7. A rear suspension unit 35 is installed between the swing arm 8 and the vehicle frame 2. The rear suspension unit buffers the force transmitted from the rear wheel 7 to the vehicle frame 2.

[0024] The rear wheel 7 contains a driven sprocket 36. A drive chain 37 runs over the driven sprocket 36 and transmits the drive power from the motor 9 to the rear wheel 7.

[0025] The engine 9 is, for example, a four-stroke internal combustion engine. The engine 9 includes a piston (not shown) that reciprocates vertically of the motorcycle 1, and a cylinder (not shown) that houses the piston. The engine 9 is located between the down tube 17 and the main frame 15. The engine 9 includes a fuel injector 38 that supplies an air-fuel mixture. The engine 9 is connected to an exhaust muffler 39 that extends to the rear of the motorcycle 1 and discharges exhaust gas from the engine 9 to the rear of the motorcycle 1.

[0026] The motorcycle 1 also includes a frame fairing 42 which covers the right and left parts of the space below the seat 28.

[0027] In the following, the swing arm 8 of the motorcycle 1 according to the embodiment of the invention will be described in detail.

[0028] Fig. 2 is a plan view of the swing arm according to the present embodiment.

[0029] Fig. 3 is a left side view of the swing arm according to the embodiment of the invention.

[0030] Fig. 4 is a cross-sectional plan view of the swing arm according to the embodiment of the invention.

[0031] Fig. 5 is an enlarged view of a part of Fig. 4.

[0032] Fig. 6 is a perspective view of the swing arm according to the embodiment of the invention, with the left arm omitted.

[0033] Fig. 7 is a partially exploded perspective view of the arms of the swing arm according to the embodiment of the invention.

[0034] As in the Fig. As shown in FIGS. 2 to 7, the swing arm 8 according to the embodiment of the invention includes a hollow body 52, a suspension fixing member 53, and a pair of arms 56. The hollow body 52 (hereinafter referred to simply as the "body") has a pivot hole 51 in which the pivot shaft 25 is disposed. The suspension fixing member 53 is located on the body 52 and is connected to one end portion of the rear suspension unit 35. The pair of arms 56 extend from the body 52 and support the respective ends of an axle 55 of the rear wheel 7.

[0035] The paired arms 56 enclose the rear wheel 7 from the right and left. In other words, the rear wheel 7 is located between the pair of arms 56. The front end portions of the respective arms 56 are fixed to the body 52. ​​The axle 55 bridges the rear ends of the respective arms 56.

[0036] Each of the arms 56 includes an outer part 51 with an open cross-section and an inner part 52 with an open cross-section.

[0037] The outer parts 61 and the inner parts 62 of the respective two arms 56 are, for example, castings. The outer parts 61 and the inner parts 62 may be workpieces formed by plastic working such as forging, extrusion, rolling, and drawing. Each of the outer parts 61 and the inner parts 62 has a cross section with an open shape (ie, a so-called open cross section) when viewed in a cross section orthogonal to its longitudinal direction ( Fig. 7), and this open cross-section has the shape of a square beam (U-shape). In other words, each of the outer parts 61 and the inner parts 62 has a cross-sectional shape like a so-called channel or gutter steel.

[0038] The outer part 61 and the inner part 62 of the right arm 56 are joined together at the respective open end portions 63 and 64, and the same applies to the left arm 56. In each of the arms 56, the outer part 61 and the inner part 62 are connected, for example, by welding or friction stir welding. In each of the arms 56, the open end portion 63 of the outer part 61 and the open end portion 64 of the inner part 62 are connected to each other. As a result, the cross section orthogonal to the longitudinal direction of the arms 56 has a cross section in a closed shape (i.e., a so-called closed cross section). The cross section orthogonal to the longitudinal direction of the arms 56 is, in particular, a rectangular cross section.

[0039] In each of the arms 56, the open end portion 63 of each outer part 61 and the open end portion 64 of the inner part 62 may have superimposed portions such that these open end portions 63 and 64 completely or partially overlap each other. In other words, the open end portion 63 of the outer part 61 may cover the outer side of the open end portion 64 of the inner part 62 in each of the arms 56. Furthermore, the open end portion 64 of the inner part 62 may cover the outer side of the open end portion 63 of the outer part 61 in each of the arms 56. Furthermore, the open end portion 64 of the inner part 62 may cover the outer side of the open end portion 63 of the outer part 61 in each of the arms 56. Furthermore, in each of the arms 56, the open end portion 64 of the inner part 62 may be provided with a flange which is inserted into the open end portion 63 of the outer part 61.Similarly, in each of the arms 56, the open end portion 63 of the outer part 61 may be provided with a flange that is inserted into the open end portion 64 of the inner part 62. In these cases, it is sufficient if the open end portion 63 of the outer part 61 and the open end portion 64 of the inner part 62 in each of the arms 56 are connected to each other at least between the open end of the outwardly oriented part (61 or 62) and the outer surface of the part (62 or 61) is located inward. The open end portion 63 of the outer part 61 and the open end portion 64 of the inner part 62 in each of the arms 56 may or may not be connected between the open end of the inwardly located part and the inner surface of the outwardly located part.Furthermore, the open end portion 63 of the outer part 61 and the open end portion of the inner part 62 in each of the arms 56 can be tapered so that the parts are connected to each other (by so-called butt welding).

[0040] In each of the arms 56, the open end portion 63 of the outer part 61 and the open end portion 64 of the inner part 62 can be straight or curved. In other words, a connecting surface 65 between the outer part 61 and the inner part 62 of each arm 56 can be straight or curved. The connecting surface 65 of each arm 56 in this embodiment is more curved toward the outer surface in the front half portion of each arm 56 than toward the inner surface of each arm.

[0041] Furthermore, the connecting surface 65 between the outer part 61 and the inner part 62 in each arm 56 may or may not pass through the center of the width dimension of each arm 56 in the vehicle's plan view. The connecting surface 65 of each arm 56 of this embodiment is closer to the inner surface of each arm 56 than the center of the width dimension of each arm 56 when viewed in the vehicle's plan view. In other words, the connecting surface 65 of each arm 56 is closer to the inner surface of each arm than to the outer surface of each arm 56 when viewed in the vehicle's plan view.

[0042] The inner surface of each arm 56 corresponds to the outer surface 66 of its inner part 62, and the outer surface of each arm 56 corresponds to the outer surface 67 of its outer part 61. The top surface of each arm 56 includes the top surface of its inner part 62 and the top surface of its outer part 61. The bottom surface of each arm 56 includes the bottom surface of its inner part 62 and the bottom surface of its outer part 61.

[0043] The body 52 and the suspension fixing part 53 are integrally formed workpieces by casting. The front half of the body 52 is fork-shaped, that is, branched to the right and left with respect to the motorcycle 1. A joint hole 51 is formed at the front end portion of the body 52. ​​The body 52 is also a hollow member. In other words, the body 52 has a cavity.

[0044] The body 52 includes a pair of right and left first opening portions 81, a pair of right and left first opening portions 81, a pair of right and left second opening portions 82, and a pair of right and left reinforcing support struts 83. The right first opening portion 81 is connected to a front edge portion 61a as an edge portion of the outer part 61 of the right arm 56, and the left first opening portion 61 is connected to the front edge portion 61a of the outer part 61 of the left arm 56. The right second opening portion 82 is connected to the outer surface 66 of the inner part 62 of the right arm 56, and the left second opening portion 82 is connected to the outer surface 66 of the inner part 62 of the left arm 56.The right reinforcement support strut 83 divides the right first opening portion 81 and the right second opening portion 82 and is connected to the front edge portion 62a as one edge portion of the inner part 62 of the right arm 56. Similarly, the left reinforcement support strut 83 divides the left first opening portion 81 and the left second opening portion 82 and is connected to the front edge portion 62a of the inner part 61 of the left arm 56.

[0045] The first opening portions 81 spatially connect the interior of the arms 56 with the cavity of the body 52. ​​In other words, the interior of the right arm 56 communicates with the cavity in the body 52 via the right first opening portion 81, and the interior of the left arm 56 communicates with the cavity of the body 52 via the left first opening portion 81. Each of the first opening portions 81 conforms to the shape of the front edge portion 61a of each outer part 61. In other words, each of the first opening portions 81 has a rectangular opening adapted to the front edge of each outer part 61 having an O-shaped cross section (i.e., a cross section in the form of a square beam). Each first opening part 81 includes three portions, which are a front edge of the outer surface 66 of the corresponding (i.e.,right or left) outer part 61, a section connected to the front edge of the top surface of the corresponding outer part 61, and a section connected to the front edge of the bottom surface of the corresponding outer part 61.

[0046] The front edge of each outer part 61 and each first opening 81 may have overlapping portions. In other words, the front edge of the outer part 61 of the right arm 56 may cover the outside of the right first opening portion 61, and the front edge of the outer part 61 of the left arm 56 may cover the outside of the left first opening portion 81. Furthermore, each first opening portion 81 may cover the outside of the front edge of the outer part 61 of the corresponding (right or left) arm 56. Furthermore, a flange may be provided at each first opening 81, which is inserted into the front edge of the corresponding outer part 61. At the front edge of each outer part 61, a flange may be provided which is inserted into the corresponding first opening portion 81. Furthermore, each first opening portion 81 and the front edge of the outer part 61 of the corresponding arm 56 may be tapered so that they are united with each other.

[0047] The second opening portions 82 spatially connect the interior space of the arms 56 with the cavity of the body 52 in a similar manner to the first opening portion 81. In other words, the interior space of the right arm 56 communicates with the cavity in the body 52 via the right first opening portion 81 and the right second opening portion 82, and the interior space of the left arm 56 communicates with the cavity in the body 52 via the left first opening portion 81 and the left second opening portion 82. Each second opening portion 82 has a shape that follows the outer surface 66 of the inner part 62 (i.e., follows the inner surface of each arm 56). Each of the second opening portions 82 has a tapered opening that becomes narrower in the vertical direction of each arm 56 as it moves away from the corresponding first opening portion 81.

[0048] Each of the reinforcement support struts 83 is installed between the top and bottom sides of the body 62. Each of the reinforcement support struts 83 is part of the body 52, which is an integrally molded workpiece. In other words, the reinforcement support struts 83 are formed integrally with the body 52. ​​Each of the reinforcement support struts 83 is thin in the inward and outward directions of the hollow body 82 and has a platform that is wide in the direction orthogonal to the inward and outward directions. In the completed state of the swing arm 8, the right reinforcement support strut 83 is located on an extension line of the inner surface of the right arm 56 (i.e., on an extension line of the outer surface 66 of the inner part 62 of the right arm 56), and the left reinforcement support strut 83 is located on an extension line of the inner surface of the left arm 56.

[0049] The suspension fixing part 53 is integrally formed on the bottom surface of the body 52. ​​As shown in Fig. 3, the suspension fixing member 53 includes a pair of right and left flanges 85. Each of the paired flanges 85 has a hole 86 so that a bolt (not shown) can be inserted through the paired holes 86 to pivotally support the rear suspension unit 35.

[0050] The first opening portions 81 and the second opening portions 82 are inclined with respect to the front-back direction of the swing arm 8. The closer the pair of first openings 81 are to the rear of the swing arm 8, the closer the pair of first openings 81 approach each other. In other words, the separation distance between the pair of first opening portions 81 becomes narrower toward the rear of the swing arm 8. The pair of second opening portions 82 are separated from each other as they approach the rear of the swing arm 8. In other words, the separation distance between the pair of second opening portions 82 becomes wider toward the rear of the swing arm 8.

[0051] That is, the right first opening portion 81 and the right second opening portion 82 are adjacent to each other with the right reinforcement support strut 83 as a boundary between them, and they are bent with the right reinforcement support strut 83 as a boundary. The same applies to the left side. The separation distance between the paired first opening portions 81 and the separation distance between the paired opening portions 82 are smallest at the point divided by the respective reinforcement support struts 83.

[0052] The suspension fixing part 53 is arranged in the area between a right zone including the right opening portions (i.e., the first and second opening portions 81 and 82 on the right side) and a left zone including the left opening portions (i.e., the first and second opening portions 81 and 82 on the left side) of the body 52 in the plan view of the motorcycle 1. The arrangement area of ​​the suspension fixing portion 53 may be on the bottom surface side or on the top surface of the body 52. ​​Moreover, the arrangement area ranges from the front edges of the respective first opening portions 81 to the rear edges of the respective second opening portions 82 in the plan view of the swing arm 8. All or part of the suspension fixing part 53 may be arranged in the area between the right zone and the left zone of the body 52 in the plan view of the motorcycle 1.

[0053] The swing arm 8 according to the embodiment of the invention includes the first opening portions 81 connected to the front edge portions 61a of the respective outer members 61, the second opening portions 82 connected to the outer surface 66 of the respective inner members 62, and the reinforcing stays 83, each of which divides the first and second opening portions 81 and 82 on the right and left sides and is connected to the front edge portion 62a (an edge part) of the inner member 62. Accordingly, the swing arm 8 is lighter than the conventional swing arm having a reinforcing wall traversing the interior of the body 52. ​​Furthermore, the swing arm 8 reinforces the connecting portion between the body 52 and the arms 56 by the reinforcing stays 83, ensuring rigidity. Furthermore, the rigidity of the swing arm 8 is increased by the reinforcing stays 83.Consequently, the swing arm 8 effectively absorbs the shock that acts via the arms 56 when the rear wheel 7 is pushed up.

[0054] Furthermore, according to the embodiment of the present invention, the swing arm 8 is equipped with the suspension fixing member 53 located in the area between the zone containing the adjacent first and second opening portions 81, 82 on the right side and the opposite zone containing the adjacent first and second opening portions 81, 82 on the left side. Accordingly, the swing arm 8 reinforces the portion acting upon the load from the rear suspension unit 35, with the reinforcing stays 83 ensuring rigidity.

[0055] Therefore, the swing arm 8 according to the embodiment of the invention is lighter than the conventional swing arm including the reinforcing wall traversing the interior of the body 52, and can ensure rigidity.

Claims

[1] Swing arm (8), comprising: - a hollow body (52) with a joint hole (51) receiving a pivot shaft (25); - a suspension fixing part (53) provided in the hollow body (52) and connected to an end portion of a suspension unit (35); - a pair of arms (56) extending from the hollow body (52) and carrying the ends of a wheel axle (55), wherein - the hollow body (52) and the suspension fixing part (53) are integrally formed workpieces by casting; - each of the paired arms (56) has an outer part (61) with an open cross-section and an inner part (62) with an open cross-section; - the outer part (61) and the inner part (62) of each arm (56) are welded together at respective open end portions (63, 64); and - the hollow body (52) has first opening sections (81) welded to a corresponding edge section (61a) of the outer part (61) of the arms (56), second opening sections (82) welded to a corresponding outer surface (66) of the inner part (62) of the arms (56), and reinforcing support struts (83) which divide the first opening sections (81) and the second opening sections (82), are welded to a corresponding front edge section of the inner part (62) of the arms (56), reinforce the connection between the hollow body (52) and the arms (56), and are installed between the top and bottom of the hollow body (52), wherein the interior of the hollow body (52) is formed without a transverse reinforcing wall. [2] Swing arm (8) according to claim 1, wherein the first opening portions (81) comprise a pair of right and left first opening portions; wherein the second opening portions (82) comprise a pair of right and left second opening portions; and wherein the suspension fixing part (53) is arranged in that region of the hollow body (52) which lies between right openings containing the right first opening section and the right second opening section and left openings containing the left first opening section and the left second opening section.

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