Body frame for motorcycle

Abstract: The present invention provides a body frame having a rigidity capable of withstanding transverse bending and torsional forces acting on middle-size and large-size on-road motorcycles. A body frame for a motorcycle includes a main pipe 3 extending over an engine 36 from a head pipe 2 for pivotally supporting a front fork and curved so as to extend downward behind the engine 36 to a pivot unit for pivotally supporting a rear swing arm 32. The main pipe 3 has a transversely elongate cross section, and is extended in a vertical plane including the longitudinal axis of the motorcycle.

Description: The present invention relates to a motorcycle having a body frame, comprising a curved main pipe extended from a head pipe for pivotally supporting a front fork over an engine to a pivot unit for pivotally supporting a rear swing arm. A known body frame for a motorcycle is formed by working a single rectangular pipe and extended in a vertical plane including the longitudinal axis of the motorcycle. FR-A-2 369 147 discloses a frame for a motorcycle of the type including a main frame which extends rearwardly and downwardly from the journal for the steerable front wheel, and which, at its lower end, is rigidly attached to a casing of the drive motor. The main frame is provided on its two side surfaces with a pair of subsidiary tubes bent to project rearwards therefrom. A pair of additional pipes extend between a lower portion of the main pipe and the subsidiary tubes to support the subsidiary tubes. A body frame for a motorcycle disclosed in Japanese Utility Model Publication No. Sho 60-39350 is constructed by extending a single main pipe (1) having a substantially square cross section backward from a head pipe (5) in a vertical plane including the longitudinal axis of the motorcycle and downward to a pivot unit for pivotally supporting a rear swing arm, extending two parallel seat rails (2) backward from a bend in a rear portion of the main pipe (1), and extending two parallel stay pipes (9) between the main pipe (1) and the seat rails (2). Thus, this known body frame has a simple framing. Since this body frame has the single main pipe, the body frame needs reinforcement to provide the body frame with a high rigidity that withstands transverse bending and torsional forces acting on the body frame when the body frame is applied to a middle-size or large-size on-road motorcycle and hence it is impossible to make use of the simple framing of the body frame. Accordingly, it is an object of the present invention to provide a body frame having a high rigidity capable of withstanding transverse bending and torsional forces acting on middle-size and large-size on-road motorcycles, and a simple construction. With the foregoing object in view, the present invention provides a motorcycle having a body frame, comprising a main pipe extended in a vertical plane including the longitudinal axis of the motorcycle and extending over an engine from a head pipe, said head pipe pivotally supporting a front fork, said main pipe being curved so as to extend downward behind the engine to a pivot unit for pivotally supporting a rear swing arm supporting a rear wheel, wherein the main pipe has a cross section transversely elongated with respect to the vertical plane in the riding position. The body frame includes the main pipe formed by working a pipe having a transversely elongate cross section, and the main pipe is extended in a vertical plane including the longitudinal axis of the motorcycle. Therefore, the body frame has a planar framing that can be easily worked and a high rigidity capable of withstanding transverse bending and torsional forces. Since the body frame has a main pipe having a transversely elongate cross section and extended in a vertical plane including the longitudinal axis, the body frame is easily worked, has a simple planar framing and has a high transverse bending rigidity and a high torsional rigidity. Accordingly, the body frame capable of securing a rigidity required of the body of a middle-size and a large-size on-road motorcycle can be easily constructed, the body frame requires reduced processing work and has a reduced number of component parts. Secondly, the body frame further includes a seat rail extended in the vertical plane including the longitudinal axis of the motorcycle for supporting a seat and connected to the rear portion of the main pipe, wherein the seat rail has a cross section transversely elongated with respect to the vertical plane. Since the seat rail is connected to the rear portion of the main pipe, has a transversely elongate cross section and is extended backward in a vertical plane including the longitudinal axis of the motorcycle, the body frame including the seat rail has a simple planar framing and has a high rigidity capable of withstanding transverse bending and torsional forces. Since the body frame has a seat rail connected to the rear portion of the main pipe so as to extend backward from the main pipe, having a transversely elongate cross section and extended in a vertical plane including the longitudinal axis of the motorcycle, the body frame including the seat rail can be easily constructed in a planar framing and has a high transverse bending rigidity and a high torsional rigidity. Thirdly, the body frame further includes down tubes extended downward from the head pipe in the vertical plane including the longitudinal axis of the motorcycle for supporting the engine at its front end and connected to the main pipe, wherein the down tubes have cross sections transversely elongated with respect to the vertical plane. Since the body frame has the down tubes for supporting the engine at its front end, connected to the main pipe, having a transversely elongate cross section and extended downward from the head pipe in a vertical plane including the longitudinal axis of the motorcycle, the body frame including the down tubes has a simple planar framing and has a high rigidity capable of withstanding transverse bending and torsional forces. Preferred embodiments of the present invention will be described with reference to the accompanying drawings. Fig. 1 is a side view of a body frame in a first embodiment according to the present invention. Fig. 2 is a plan view of the body frame of Fig. 1. Fig. 3 is a sectional view taken on line A-A in Fig. 1. Fig. 4 is a sectional view taken along the arrow B in Fig. 1. Fig. 5 is a perspective view of the body frame of Fig. 1. Fig. 6 is a side view of a motorcycle employing the body frame of Fig. 1. Fig. 7 is a sectional view taken on line C-C in Fig. 6. Fig. 8 is a side view of a body frame in a second embodiment according to the present invention. Fig. 9 is a plan view of the body frame of Fig. 8. Fig. 10 is a side view of a motorcycle employing the body frame of Fig. 8. Figs. 11 a and 11 b are perspective views of modifications of the embodiments of the present invention. Fig. 12 is a perspective view of a body frame in another modification of the embodiment of the present invention. Fig. 13 is a sectional view taken on line D-D in Fig. 12. Referring to Fig. 1 showing a body frame 1 in a first embodiment according to the present invention in a side view, the body frame includes, as principal components, a main pipe 3 extending backward from a head pipe 2 for supporting a front fork, and a seat rail 4 extended backward from the main pipe 3. A pair of down tubes 6 are extended downward on the opposite sides of the longitudinal axis of the motorcycle, respectively, from a gusset plate 5 extended across the head pipe 2 and the main pipe 3, and a pair of stay pipes 7 are extended between a lower portion of the main pipe 3 and the seat rails 4 on the opposite sides of the longitudinal axis to support the seat rail 4. Each down tube 6 is formed by working a rectangular pipe and each stay pipe 7 is formed by working a rectangular pipe. Front hangers 8 for supporting an engine at its front part are attached to the lower ends of the down tubes 6. The main pipe 3 is formed by working a rectangular pipe, is extended backward from the head pipe 2, and a rear portion of the main pipe 3 is curved downward at a bend. A pivotal bearing part 9 and rear hangers 10 for supporting the engine at its rear part are attached to the lower end of the rear portion of the main pipe 3. The seat rail 4 is formed by working a rectangular pipe and extended backward from a portion of the main pipe 3 near the bend. Gusset plates 11 are extended across the main pipe 3 and the seat rail 4, and support members 12 for supporting rear shock absorbers are attached to the gusset plates 11. Referring to Fig. 2 showing the body frame 1 in a plan view, each of the main pipe 3 and the seat rail 4, i.e., essential components of the body frame 1, is a single pipe curving in a vertical plane including the longitudinal axis. Therefore, the body frame 1 has a simple planar framing. Each of the parallel stay pipes 7 is formed by working a rectangular pipe. The stay pipes 7 support the seat rail 4. The stay pipes 7 are bent in an outward convex shape so that the same may not interfere with rear shock absorbers provided in a vertical plane including the longitudinal axis. The body frame 1 has a relatively small lateral size and has a slim shape. Fig. 3 is a sectional view taken on line A-A in Fig. 1. The main pipe 3 is a flat pipe having a transversely elongate, rectangular cross section. More concretely, the width W of the transversely elongate cross section of the main pipe 3 is about 1.7 to about 2.2 times the height H of the same. The transverse bending rigidity and the torsional rigidity of the flat pipe having the rectangular cross section are about 5 to about 10 times those of a square pipe having a square cross section. The seat rail 4 has a cross section similar to that of the main pipe 3. Thus, the body frame 1 formed by joining together the pipes of such cross sections in a planar framing has a transverse bending rigidity and a torsional rigidity equivalent to those of the component members. Since the body frame 1 is constructed by joining together the pipes extending in a vertical plane including the longitudinal axis in a planar framing, the body frame 1 does not need any cross members for interconnecting parallel pipes, and can be easily completed by assembling a relatively small number of members. Thus, the body frame 1 has a simple framing and a high transverse bending rigidity and a high torsional rigidity. Fig. 4 is a view taken along the arrow B in Fig. 1. Substantially U-shaped plates 26 are attached to the opposite sides of the lower portion of the main pipe 3, respectively, to form a boxlike part 28, the lower ends of the stay pipes 7 are fixed to the upper ends of the boxlike part 28, the rear hangers 10 are attached to the opposite side surfaces of the boxlike part 28, and a bearing pipe 27 is extended through and across the boxlike part 28 to form a pivotal bearing part 9. Indicated at 7a is a cross member extended between the stay pipes 7. Referring to Fig. 5 showing the body frame 1 of Fig. 1 in a perspective view, fuel tank mounting members 21a and 21b, a seat support member 22, a front seat retaining member 23, a rear seat retaining member 24 and a seat locking member 25 are attached to the main pipe 3 and the seat rail 4 formed by working the rectangular pipes having transversely elongate cross sections. Those members can be easily attached to the flat surfaces of the rectangular pipes without requiring special fixing jigs for fixedly positioning the members on the main pipe 3 and the seat rail 4, respectively. Referring to Fig. 6 showing a motorcycle employing the body frame of Fig. 1 in a side view, a front fork 31 is supported on the head pipe 2 of the body frame 1, a rear swing arm 32 is supported on the pivotal bearing part 9, shock absorbers 33 are connected to the rear swing arm 32 to support the body frame 1 at its rear part, a fuel tank 34 and a seat 35 are mounted on the body frame 1, and an engine 36 and an exhaust pipe 37 are supported under the body frame 1. Fig. 7 is a sectional view taken on line C-C in Fig. 6. The pivotal bearing part 9 has the bearing pipe 27 held on the boxlike part 28, and a bolt 30 extending through the bearing pipe 27 and the plates 29. The rear swing arm 32 is supported pivotally on the bolt 30. The plates 26 forming the boxlike part 28 secure a sufficiently high rigidity capable of withstanding bending in a vertical plane and twisting in a horizontal plane for the boxlike part 28. The body frame 1 of the motorcycle thus constructed has the main pipe and the seat rail formed by working rectangular pipes each having a laterally elongate cross section. Therefore, the main fame has a simple planar framing, and ensures transverse bending and torsional rigidities capable of withstanding transverse bending and torsional forces. Thus, the body frame having a high rigidity required by middle-size and large-size motorcycles can be easily constructed at a relatively low manufacturing cost. Referring to Fig. 8 showing a body frame 41 in a second embodiment according to the present invention in side view, the body frame 41 has a down tube 42 extended downward from a head pipe 2 and having a lower portion 42a curved so as to extend backward, and a main pipe 43 extended backward from the head pipe 2 and having a rear portion curved downward. The lower rear end of the down tube 42 is joined to the lower end of the main pipe 43 to form a cradlelike frame unit. A round pipe 44 is extended between the down tube 42 and the main pipe 43. The joint of the head pipe 2, the down tube 42 and the main pipe 43 is reinforced by a gusset plate 45. A straight seat rail 46 formed by working a rectangular pipe is extended backward from a portion of the main pipe 43 near a bend in the main pipe 43, and stay pipes 47 are extended between the seat rail 46 and a rear down portion 43a of the main pipe 43 to support the seat rail 46. The lower front ends of the stay pipes 47 are fixed to the opposite side surfaces of the rear down portion 43a of the main pipe 43. Rear shock absorber support members 48 are attached to the rear down portion 43a of the main pipe 43 at a position above the lower front ends of the stay pipes 47. A pivotal bearing part 49 is formed in the lower down portion 43a of the main pipe 43 at a position below the lower front ends of the stay pipes 47. The down tube 42 and the main pipe 43 are formed by working square pipes having substantially square cross sections, respectively, and the seat rail 46, the lower portion 42a of the down tube 42 and the rear down portion 43a of the main pipe 43 are formed by working rectangular pipes each having a transversely elongate, rectangular cross section. The width of the cross section of each of these rectangular pipes is 2 to 3 times the height of the same. A taper portion 42b having a continuously varying cross section, i.e., a continuously varying width and a continuously varying height, is formed between the upper front portion and the lower portion 42a of the down tube 42 to avoid stress concentration in any portion of the down tube 42. Similarly, joint plates 43b, each being formed substantially in a triangular shape, are attached to the joint of the front portion and the rear down portion 43a of the main pipe 43. The taper portion 42b and the joint plates 43b enables the use of rectangular pipes having rectangular portions having increased widths, respectively, to secure a necessary rigidity of the body frame 41. Referring to Fig. 9 showing the body frame 41 of Fig. 8 in a plan view, the rectangular pipes forming the down tube 42, the main pipe 43 and the seat rail 46 are extended in a vertical plane including the longitudinal axis to form the body frame 41 in a planar shape. The stay pipes 47 are formed by working two rectangular pipes and are bent in an outward convex shape so that the same may not interfere with rear shock absorbers. The stay pipes 47 support the seat rail 46. The body frame 41 has a relatively small lateral size and has a slim shape. Referring to Fig. 10 showing a motorcycle employing the body frame 41 of Fig. 8 in a side view, an engine 36 is mounted on the cradlelike body frame 41 having the lower portion 42a having an increased width, and a front fork 31 and a rear swing arm 32 are supported on the body frame 41. Shock absorbers 33 are extended between the rear swing arm 32 and the body frame 41 to support the rear portion of the body frame 41. A fuel tank 34, a seat 35 and the component parts of the motorcycle are mounted on the body frame 41 to construct the motorcycle. The cradlelike body frame 41 built by assembling the main pipe 43, the seat rail 46 and the down tube 42 formed by working rectangular pipes and extended in a vertical plane including the longitudinal axis with the widths thereof transversely extended has a simple planar framing, reduces load on the engine 36 and has a high rigidity capable of withstanding transverse bending and torsional forces. Figs. 11a and 11b are perspective views of body frames 51 and 52 in modifications of the first and the second embodiment of the present invention, respectively. The body frame 51 (52) of Fig. 11a (11b) has a stay pipe 53 (53) supporting a seat rail 4 (46) having a transversely elongate cross section and formed by working a rectangular pipe. The stay pipe 53 (53) is extended between a main pipe 3 (43) and the seat rail 4 (46) in a vertical plane including the longitudinal axis. The body frames 51 and 52 have each a simple planar shape. A motorcycle employing the body frame 51 or 53 may be provided with one rear shock absorber disposed on one side of the stay pipe 53. Fig. 12 is a perspective view of a body frame 61 in a further modification of the foregoing embodiment of the present invention, and Fig. 13 is a sectional view taken on line D-D in Fig. 12. The body frame 61 has a main pipe 62, a seat rail 63 joined to a rear portion of the main pipe 62, a stay pipe 64 and a down tube 65 extending under the main pipe 62. Each of those members of the body frame 61 is formed by working a flat pipe having an elliptic cross section. The width W, i.e., the transverse size, of the elliptic cross section of each flat pipe is greater than the height H of the same. Use of these flat pipes secures a necessary rigidity for the body frame 61. The flat upper and the flat lower surfaces of the flat pipes facilitate work for attaching the component parts of the motorcycle to the body frame 61, and the round side walls of the flat pipes enable characteristic design. Since the rigidity of each of the foregoing body frames is dependent on the transverse bending rigidities and the torsional rigidities of the component members, the component members may be formed from flat pipes of any suitable cross section. Therefore, a pipe having an elliptic cross section has the same effect as that of a pipe having a rectangular cross section in securing a necessary rigidity for the body frame.

Claims: A motorcycle having a body frame (1; 41; 51; 52; 61), comprising a main pipe (3; 43; 62) extended in a vertical plane including the longitudinal axis of the motorcycle and extending over an engine (36) from a head pipe (2), said head pipe (2) pivotally supporting a front fork (31), said main pipe being curved so as to extend downward behind the engine (36) to a pivot unit (9; 49) for pivotally supporting a rear swing arm (32) for supporting a rear wheel, wherein the main pipe (3; 43; 62) has a cross section transversely elongated with respect to the vertical plane in the riding position. A motorcycle having a body frame (1; 41; 51; 52; 61) according to claim 1, further comprising a seat rail (4; 46; 63) extended in the vertical plane including the longitudinal axis of the motorcycle for supporting a seat (35) and connected to the rear portion of the main pipe (3; 43; 62), wherein the seat rail (4; 46; 63) has a cross section transversely elongated with respect to the vertical plane. A motorcycle having a body frame (1; 41; 51; 52; 61) according to claim 1, further comprising down tubes (6; 42; 65) extended downward from the head pipe (2) in the vertical plane including the longitudinal axis of the motorcycle for supporting the engine (36) at its front end and connected to the main pipe (3; 43; 62), wherein the down tubes (6; 42; 65) have cross sections transversely elongated with respect to the vertical plane.

Inventors: ITOH HIROYUKI, KAWASHIMA KAZUHIRO, YAMAGUTCH KEN, ITOH, HIROYUKI, KAWASHIMA, KAZUHIRO, YAMAGUTCH, KEN
Applicants: HONDA MOTOR CO LTD, HONDA GIKEN KOGYO KABUSHIKI KAISHA
Application year: 1996
Main classification: B62K19
IPC codes: B62K19, B62K11