Bicycle with assist motor

Abstract: To provide a bicycle with an assist motor, which includes rear fork legs (6 R , 6 L ) capable of easily avoiding the interference with a power unit (P) and a chain (12) with a simple and lightweight structure. A chain (12) for transmitting a torque of a crank shaft (7) provided at a lower end of a body frame (1) to a rear wheel (Wr) is disposed on the right side of a vehicular body, and a power unit (P) for transmitting a torque of an assist motor (13) to the chain (12) is disposed on the body frame (1) in the vicinity of the crank shaft (7). Of a pair of right and left rear fork legs (6 R , 6 L ) extending rearward from the body frame (1), the rear fork leg (6 R ) disposed on the same side as that of the chain (12) is composed of a front half portion (6 4 ) and a rear half portion (6 5 ) which are bent at an intermediate portion (6 3 ), wherein the front half portion (6 4 ) is connected at a front end thereof to the body frame (1) and extends rearward, downward of the vehicular body through the upper side of the power unit (P) and the rear half portion (6 5 ) extends rearward of the vehicular body while passing through a rotating plane of the chain (12) from the inner side to the outer side of the vehicular body.

Description: Technical Field of the Invention The present invention relates to a bicycle with an assist motor in which a torque of a crank shaft and a torque of a power unit are transmitted to a rear wheel via a chain. Related Art The bicycle with an assist motor of this type is known, for example, from Japanese Patent Laid-open No. Sho 58-89483. Problem to be Solved by the Invention In the bicycle with an assist motor described in the above document, Japanese Patent Laid-open No. Sho 58-89483, a power unit is supported on rear fork legs, and therefore, there arise a problem that not only the structure of the rear fork legs becomes complicated for avoiding the interference with a chain disposed along the rear fork legs and the power unit, but also the rear fork legs become larger in size and thereby in weight for supporting the weight of the power unit. In view of the foregoing, the present invention has been made, and an object of the present invention is to provide a bicycle with an assist motor, which includes rear fork legs capable of easily avoiding the interference with a power unit and chain with a simple and lightweight structure. Means for Solving the Problem To achieve the above object, according to the present invention, there is provided a bicycle with an assist motor, including a crank shaft rotated by crank pedals and supported in the vicinity of a lower end of a body frame formed in a substantially V-shape in a side view, wherein a torque of the crank shaft is transmitted to a rear wheel supported at rear ends of a pair of right and left rear fork legs connected at front ends thereof to the body frame via a chain disposed on one side of a vehicular body in the width direction and a torque of a power unit supported in the vicinity of the lower end of the body frame is transmitted to the rear wheel via the chain, characterized in that one rear fork leg disposed on one side of the vehicular body in the width direction is composed of a front half portion and a rear half portion which are integrally continuous to each other via an intermediate bent portion; and the front half portion is connected at a front end thereof to the vicinity of the lower end of the body frame and extends rearward, downward of the vehicular body through an upper side of a main body of the power unit, and the rear half portion extends rearward of the vehicular body while passing through a rotating plane of the chain from the inner side to the outer side of the vehicular body. Effect of the Invention As:described above, according to the present invention, since the power unit is supported on the body frame, it is possible to reduce a load applied to the rear fork legs and hence to make smaller the size and weight of the rear fork legs. Moreover, since the rear fork leg on the same side as that of the chain is bent at the intermediate bent portion and is disposed such that the front half portion is connected at the front end thereof to the vicinity of the lower end of the body frame and extends rearward, downward of the vehicular body through the upper side of the main body of the power unit and the rear half portion extends rearward of the vehicular body while passing through a rotating plane of the chain from the inner side to the outer side of the vehicular body, it can reasonably avoid the interference with the power unit and the chain in spite of the simple shape. Preferred Embodiments of the Invention Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings. Brief Description of the Drawings Fig. 1 A side view showing the entire configuration of a motor with an assist motor. Fig. 2 An enlarged view of essential portions shown in Fig. 1. Fig. 3 A view seen from the direction shown by an arrow 3. Fig. 4 An enlarged view showing essential portions shown in Fig. 2. Fig. 5 A sectional view taken on line 5-5 of Fig. 4. Fig. 6 An enlarged view showing essential portions shown in Fig. 5. Fig. 7 A sectional view taken on line 7-7 of Fig. 6. Fig. 8 A sectional view taken on line 8-8 of Fig. 6. Fig. 9 A sectional view taken on line 9-9 of Fig. 6. Fig. 10 A view, similar to Fig. 2, showing a second embodiment of the present invention. Fig. 11 An enlarged sectional view taken on line 11-11 of Fig. 10. Fig. 12 A view, similar to Fig. 2, showing a third embodiment of the present invention. Figs. 1 to 9 show a first embodiment of the present invention, wherein Fig. 1 is a side view showing the entire configuration of a bicycle with an assist motor; Fig. 2 is an enlarged view showing essential portions shown in Fig. 1; Fig. 3 is a view seen from the direction shown by an arrow 3 of Fig. 2; Fig. 4 is an enlarged view showing essential portions shown in Fig. 2; Fig. 5 is a sectional view taken on line 5-5 of Fig. 4; Fig. 6 is an enlarged view showing essential portions shown in Fig. 5; Fig. 7 is a sectional view taken on line 7-7 of Fig. 6; Fig. 8 is a sectional view taken on line 8-8 of Fig. 6; and Fig 9 is a sectional view taken on line 9-9 of Fig. 6. As shown in Fig. 1, a bicycle B includes a body frame 1 formed in a V-shape in a side view, and a handlebar 4 and a front wheel Wf are respectively supported at upper and lower ends of a front fork 3 pivotably supported by a head pipe 2 provided at a front end of the body frame 1. A rear wheel Wr is supported by a pair of right and left rear fork legs 6 R , 6 L reinforced by stays 5, 5 extending rearward from the vicinity of a lower end of the body frame 1. A crank shaft 7 rotatably supported at the lower end of the body frame 1 includes a pair of right and left crank arms 8 R , 8 L having at leading ends thereof crank pedals 9 R , 9 L respectively. A crank shaft sprocket 10 rotated by the crank shaft 7 is connected to a rear wheel sprocket 11 provided on an axle of the rear wheel Wr by way of a chain 12. When the crank shaft 7 is rotated by a step-on force of the crank pedals 9 R , 9 L , the rotation of the crank shaft 7 is transmitted to the rear wheel Wr via the crank shaft sprocket 10, chain 12, and rear wheel sprocket 11. An assist motor 13 provided under the body frame 1 and connected to the crank shaft sprocket 10 serves to generate a drive force for assisting the step-on force of the crank pedals 9 R , 9 L . A battery box 14 provided on a front portion of the body frame 1 contains a running battery 15 composed a plurality of Ni-Cd cells for driving the assist motor 13, and a main switch 16 is provided at a front end of the battery box 14. A controller 17 such as an electronic control unit for controlling the driving of the assist motor 13 and a motor driver is provided at a rear portion of the body frame 1. As can be seen from Figs. 2 and 3, a pair of right and left gussets 18 R , 18 L are welded to the lower end of the V-shaped body frame, and a front, upper portion of a power unit P including the assist motor 13 is held between these gussets 18 R , 18 L and fixed thereto by means of two bolts 19, 20. The right and left rear fork legs 6 R , 6 L have flat portions 6 1 , 6 1 at front ends thereof and flat portions 6 2 , 6 2 at rear ends thereof. The front flat portions 6 1 , 6 1 are connected to rear, upper portions of the gussets 18 R , 18 L , and the rear flat portions 6 2 , 6 2 are connected to the axle 22 of the rear wheel Wr and the stays 5, 5 via axle supporting member 21, 21. The rear fork legs 6 R , 6 L include front half portions 6 4 , 6 4 , intermediate bent portions 6 3 , 6 3 , and rear half portions 6 5 , 6 5 in the longitudinal direction. The front half portions 6 4 , 6 4 extend rearward, downward of the vehicular body in a side view and also extend outward of the vehicular body in a plan view; while the rear half portions 6 5 , 6 5 extend rearward of the vehicular body both in a side view and in a plan view. In Fig. 2, the left rear fork leg 6 L on the viewer's side of the drawing is partially cutaway so that the right rear fork leg 6 R on the opposed side of the drawing is viewed. The chain 12 connecting the crank shaft sprocket 10 to the rear wheel sprocket 11 is disposed on the right side of the center of the vehicular body and has a vertical rotating plane, with the right surface of the chain 12 covered with a chain cover 23. The rear portion of the chain cover 23 has an opening portion 23 1 (see Fig. 2) extending in the longitudinal direction, and the rear half portion 6 5 of the right side rear fork portion 6 R extends from the inner side to the outer side of the vehicular body while passing through the rotating plane of the chain 12 and the opening portion 23 1 of the chain cover 23. Next, the structure of the power unit P will be described in detail with reference to Figs. 4 to 9. A housing 31 of the power unit P includes right and left housings 33, 34 connected to each other by means of a plurality of bolts 32, ..., 32, and a left cover 35 removably covering an opening portion of the left housing 34. The assist motor 13 is mounted on a right surface of a rear portion of the left housing 34 with an output shaft 36 thereof directed leftward of the vehicular body, and in such a mounted state, the assist motor 13 is positioned on the left side of the rotational plane of the chain 12 disposed on the right side of the vehicular body. A first intermediate shaft 37 disposed forward, downward of the output shaft 36 of the assist motor 13 is supported at both ends thereof by the right and left housings 33, 34 via ball bearings 38, 39 respectively. A second intermediate shaft 40 disposed forward of the first intermediate shaft 37 and rearward, downward of the crank shaft 7 is supported at both ends thereof by the right and left housings 33, 34 via ball bearings 41, 42 respectively. A primary gear 43 fixed on the output shaft 36 of the assist motor 13 is meshed with a first intermediate gear 44 fixed on the first intermediate shaft 37; a second intermediate gear 45 formed integrally with the first intermediate shaft 37 is meshed with a third intermediate gear 47 supported by the second intermediate shaft 40 via a first one-way clutch 46 (see Fig. 5); and a fourth intermediate gear 48 formed integrally with the second intermediate shaft 40 is meshed with a final gear 49 relatively rotatably supported at a right end of the crank shaft 7. The left surfaces of the primary gear 43 and the first intermediate gear 44 face the left cover 35 removably mounted on the left housing 34. The primary gear 43, first intermediate gear 44, second intermediate gear 45, third intermediate gear 47, fourth intermediate gear 48, and final gear 49 constitute a power transmission mechanism D. As can be seen from Fig. 5, the power transmission mechanism D is disposed on the left side of the rotating plane of the chain disposed on the right side of the vehicular body. The final gear 49 is supported on the right housing 33 via a ball bearing 50, and the right end of the crank shaft 7 is supported at the center of the final gear 49 via a roller bearing 51. The crank shaft sprocket 10 is connected by a nut 52 around a cylindrical shaft portion 49 1 of the final gear 49 extending rightward of the vehicular body from the right housing 33. The left end of the crank shaft 7 is supported on the left housing 34 via a ball bearing 53. Accordingly, when the assist motor 13 is rotated, a torque of the output shaft 43 of the assist motor 13 is transmitted to the crank shaft sprocket 10 via the primary gear 43, first intermediate gear 44, first intermediate shaft 37, second intermediate gear 45, third intermediate gear 47, first one-way clutch 46, second intermediate shaft 40, fourth intermediate gear 48, and final gear 49. On the other hand, when the driving of the assist motor 13 is stopped by discharge of the running battery 15 or the like, the first one-way clutch 46 idles so as not to obstruct the rotation of the crank shaft sprocket 10 due to the step-on force of the crank pedals 9 R , 9 L . As can be seen from Figs. 6 to 8, a torsion bar 61 mounted in a slit 7 1 formed in the crank shaft 7 along the axial line has a columnar shaft portion 61 1 rotatably fitted between right and left inner wall surfaces 7 2 , 7 2 of the slit 7 1 and a pair of arm portions 61 2 , 61 3 projecting radially from right and left ends of the shaft portion 61 1 . The left arm portion 61 2 of the torsion bar 61 is closely fitted between the right and left inner wall surfaces 7 2 , 7 2 of the slit 7 1 and integrally connected to the crank shaft 7. A rotational speed detecting gear 62 is press-fitted around the outer periphery of the arm portion 61 2 and the crank shaft 7 (see Fig. 7). Thus, the left end of the torsion bar 61 and the rotational speed detecting gear 62 are integrally connected to the left end of the crank shaft 7. The right arm portion 61 3 of the torsion bar 61, which is loosely fitted between the right and left inner wall surfaces 7 2 , 7 2 of the slit 7 1 , has gaps α, α between the inner wall surfaces 7 2 , 7 2 and the same, and accordingly, the right end of the torsion bar 61 can be torsionally deformed with respect to the left end thereof in a range: of the gaps α, α (see Fig. 8). In addition, a crank shaft rotational speed sensor 73 supported on the left housing 34 is disposed opposite to the outer periphery. of the rotational speed detecting gear 62 (see Fig. 5). As can be seen from Figs. 6 to 8, a second one-way clutch 63 is disposed around the outer periphery of the right end of the crank shaft 7. The second one-way clutch 63 includes a plurality of claws 65, ..., 65 between an outer ring 49 2 formed integrally with the final gear 49 and an inner ring 64 relatively rotatably fitted around the outer periphery of the crank shaft 7, and the arm portion 61 3 at the right end of the torsion bar 61 is locked in a recess 64 1 formed in the inner periphery of the inner ring 64. When the crank shaft 7 is normally rotated by the step-on force of the crank pedals 9 R , 9 L , the torque of the crank shaft 7 is transmitted to the crank shaft sprocket 10 via the torsion bar 61, second one-way clutch 63, and final gear 49. When the crank shaft 7 is reversely rotated by the step-on force of the crank pedals 9 R , 9 L , the second one-way clutch 63 is slipped to allow the reverse rotation of the crank shaft 7. When the torque in the direction shown by an arrow "a" in Fig. 8 is inputted from the crank pedals 9 R , 9 L to the crank shaft 7, the inner ring 64 to which a load of the rear wheel Wr is transmitted via the cylindrical shaft portion 49 1 of the final gear 49 and the clutch claws 65, ..., 65 resists the torque in the direction shown by the arrow "a", so that the arm portion 61 3 at the right end of the torsion bar 61 is torsionally deformed in the direction shown by an arrow "b" with respect to the crank shaft 7, with a result that a relative rotation corresponding to the torque inputted to the crank shaft 7 is generated between the crank shaft 7 and the inner ring 64. As can be seen from Fig. 6, an inner slider 66 is supported around the outer periphery of the crank shaft 7 in such a manner as not to be relatively rotatable but to be axially slidable with respect to the crank shaft 7, and an outer slider 68 is relatively rotatably supported around the outer periphery of the inner slider 66 via a plurality of balls 67. A detecting lever 70 pivotably supported at one end thereof on the left housing 34 via a supporting pin 69 is, at an input portion 70 1 thereof positioned at the intermediate portion in the longitudinal direction, brought in contact:with the outer slider 68 and is also, at the other end thereof, brought in contact with a probe 71 1 of a stroke sensor 71 provided on the left housing 34. The detecting lever 70 is biased by a spring 72 contractedly provided between the left housing 34 and the same so that the input portion 70 1 is brought in elastic-contact with the outer slider 68. As can be seen from Figs. 6 and 9, an recessed cam face 64 2 is formed in an end surface of the inner ring 64 of the second one-way clutch 63, and a projecting cam face 66 1 to be engaged with the cam face 64 2 is formed on an end surface of the inner slider 66. Next, the function of the embodiment having the above-described configuration according to the present invention will be described. When a driver steps on the crank pedals 9 R , 9 L for running the bicycle, the crank shaft 7 is rotated via the crank arms 8 R , 8 L , and the torque of the crank shaft 7 is transmitted from the torsion bar 61 to the rear wheel Wr via the second one-way clutch 63, final gear 49, crank shaft sprocket 10, chain 12, and rear wheel sprocket 11. At this time, the magnitude of the step-on force of the crank pedals 9 R , 9 L is detected by the stroke sensor 71. Specifically, when the torque corresponding to the step-on force of the crank pedals 9 R , 9 L is applied to the torsion bar 61, a relative rotation corresponding to the torsional angle of the torsion bar 61 is generated between the inner ring 64 of the second one-way clutch 63 and the inner slider 66. When the arm portion 61 3 of the torsion bar 61 is torsionally deformed with respect to the crank shaft 7, the inner slider 66 supported on the crank shaft 7 in such a manner as not to be relatively rotatable but to be slidable axially with respect to the crank shaft 7 is, as shown in Fig. 9, rotated in the direction shown by an arrow "c" relative to the inner ring 64 of the second one-way clutch 63 connected to the arm portion 61 3 of the torsion bar 61. As a result, the cam face 66 1 of the inner slider 66 is pressed to the cam face 64 2 of the inner ring 64, so that the inner slider 66 is slid against the elastic force of the spring 72 along the crank shaft 7 in the direction shown by an arrow "d". Thus, the detecting lever 70 with the input portion 70 1 pressed by the outer slider 68 slid together with the inner slider 66 is rocked around the supporting pin 69 to press the probe 71 1 of the stroke sensor 71. At this time, since the stroke of the probe 71 1 of the stroke sensor 71 is proportional to the torsional amount of the torsion bar 61, that is, the step-on force of the crank pedals 9 R , 9 L , it is possible to detect the step-on force on the basis of the output of the stroke sensor 71. Accordingly, the controller 17 performs duty control for the driving of the assist motor 13 on the basis of the output of the stroke sensor 71 for detecting the step-on force of the crank pedals 9 R , 9 L and the output of the crank shaft rotational speed sensor 73 for detecting the rotational speed of the crank shaft 7. The duty ratio of the duty control is set so as to be increased linearly with the rotational speed of the assist motor 13 (that is, the output of the crank shaft rotational speed sensor 73), and to be increased linearly with the step-on force of the crank pedals 9 R , 9 L (that is, the output of the stroke sensor 71). As can be seen from Figs. 4 and 5, since the assist motor 13 has the output shaft 36 disposed in the width direction of the crank shaft 7, that is, in parallel to the crank shaft 7, each of the gears constituting the power transmission mechanism D for transmitting a torque from the output shaft 36 to the crank shaft sprocket 10 can be composed of a spur gear or helical gear, to thereby improve the power transmission efficiency and to reduce the manufacturing cost. Moreover, since the power transmission mechanism D is disposed so as to be shifted leftward of the vehicular body from the rotational plane of the chain 12 disposed on the right side of the vehicular body, it becomes possible to realize the reasonable layout of the power transmission mechanism D without interference with the chain 12 and hence to increase the space efficiency, and also to move the assist motor 13 at an arbitrary position around the crank shaft 7 without a large change in the structure of the power transmission mechanism D and hence to significantly increase the degree of freedom in design. Additionally, in this embodiment, the front half portion 6 4 of the right rear fork leg 6 R is connected to the vicinity of the bent portion of the lower end of the body frame 1 over the power unit P, extending downward, rearward therefrom, and reaches the rear side of the vehicular body through the upper side of the power unit P; and the rear half portion 6 5 connected to the rear portion of the front half portion 6 4 extends rearward of the vehicular body and passes through the rotating plane of the chain 12 from the inner side to the outside of the vehicular body, and accordingly, only by provision of the rear fork leg 6 R having a simple shape in which the front half portion 6 4 and the rear half portion 6 5 are bent at the intermediate bent portion 6 3 , it is possible to avoid the interference of the rear fork leg 6 R with the power unit P and the chain 12. This makes it possible to obtain the rear fork leg 6 R excellent in strength and low in manufacturing cost, and to increase the degree of freedom in design of the power unit P. Figs. 10 and 11 show a second embodiment of the present invention, wherein Fig. 10 is similar to Fig. 2, and Fig. 11 is an enlarged sectional view taken on line 11-11 of Fig. 10. In the second embodiment, the structure of the power transmission mechanism D for transmitting a torque from the assist motor 13 to the crank shaft sprocket 10 is partially different from that in the first embodiment. The second embodiment is so configured that the assist motor 13 is positioned higher than the upper end of the chain 12 in a side view and thereby the distance between the output shaft 36 of the assist motor 13 and the first intermediate shaft 37 is increased more than that in the first embodiment. Consequently, the power transmission from the output shaft 36 of the assist motor 13 to the first intermediate shaft 37 is performed by provision of an endless chain 74 between a primary sprocket 43' provided on the output shaft 36 and a first intermediate sprocket 44' provided on the first intermediate shaft 37. A tension sprocket 75 for adjusting the tension of the endless chain 74 is brought in contact with an intermediate portion of the endless chain 74 (see Fig. 10). In addition, in the second embodiment, the assist motor 13, which is part of the power unit P, projects upward from the rear fork legs 6 R , 6 L in a side view; however, since the main body of the power unit P (that is, the portion excluding the assist motor 13) is positioned under the rear fork legs 6 R , 6 L , the main body does not interfere with the rear fork legs 6 R , 6 L . Next, a third embodiment of the present invention will be described with reference to Fig. 12. The third embodiment is a modification of the second embodiment, in which the layout of the power transmission mechanism D is different from that of the second embodiment. Specifically, the assist motor 13 is disposed in front of the crank shaft 7; the first intermediate shaft 37 is disposed behind and under the assist motor 13; and the second intermediate shaft 38 is disposed behind the first intermediate shaft 37 and under the crank shaft 7. The third embodiment exhibits the same operational effect as those in the first and second embodiments. While the preferred embodiments of the present invention have been described using the specific terms, such description is for illustrative purposes only, and it is to be understood that many changes in design may be made without departing from the scope of the present invention. To provide a bicycle with an assist motor, which includes rear fork legs capable of easily avoiding the interference with a power unit and a chain with a simple and lightweight structure. A chain 12 for transmitting a torque of a crank shaft 7 provided at a lower end of a body frame 1 to a rear wheel Wr is disposed on the right side of a vehicular body, and a power unit P for transmitting a torque of an assist motor 13 to the chain 12 is disposed on the body frame 1 in the vicinity of the crank shaft 7. Of a pair of right and left rear fork legs 6 R , 6 L extending rearward from the body frame 1, the rear fork leg 6 R disposed on the same side as that of the chain 12 is composed of a front half portion 6 4 and a rear half portion 6 5 which are bent at an intermediate portion 6 3 , wherein the front half portion 6 4 is connected at a front end thereof to the body frame 1 and extends rearward, downward of the vehicular body through the upper side of the power unit P and the rear half portion 6 5 extends rearward of the vehicular body while passing through a rotating plane of the chain 12 from the inner side to the outer side of the vehicular body.

Claims: A bicycle with an assist motor, including a crank shaft (7) rotated by crank pedals (9 R , 9 L ) and supported in the vicinity of a lower end of a body frame (1) formed in a substantially V-shape in a side view, wherein a torque of said crank shaft (7) is transmitted to a rear wheel (Wr) supported at rear ends of a pair of right and left rear fork legs (6 R , 6 L ) connected at front ends thereof to said body frame (1) via a chain (12) disposed on one side of a vehicular body in the width direction and a torque of a power unit (P) supported in the vicinity of the lower end of said body frame (1) is transmitted to said rear wheel (Wr) via said chain (12), characterized in that one rear fork leg (6 R ) disposed on one side of the vehicular body in the width direction is composed of a front half portion (6 4 ) and a rear half portion (6 5 ) which are integrally continuous to each other via an intermediate bent portion (6 3 ); and said front half portion (6 4 ) is connected at a front end thereof to the vicinity of the lower end of said body frame (1) and extends rearward, downward of the vehicular body through an upper side of a main body of said power unit (P), and said rear half portion (6 4 ) extends rearward of the vehicular body while passing through a rotating plane of said chain (12) from the inner side to the outer side of the vehicular body. A bicycle according to claim 1, characterized in that the assist motor (13) comprises an output shaft (36) which is disposed spaced apart from the crank shaft (7) in its width direction. A bicycle according to claim 1 or 2, characterized in that a power transmission mechanism (D) for transmitting a torque from the assist motor (13) to the crank shaft (7) is disposed on the vehicular body generally on the opposite side of the chain (12).

Inventors: MORIIWA TAKEHITO, MORIIWA, TAKEHITO, Moriiwa, Takehito, K.K. Honda Gijutsu Kenkyusho
Applicants: HONDA MOTOR CO LTD, HONDA GIKEN KOGYO KABUSHIKI KAISHA
Application year: 1997
Main classification: B62M23
IPC codes: B62K11, B62M6