A power-assisted bicycle includes a front wheel, a rear wheel, a body frame, a bracket that mounts a power unit, and a power unit fixed to the bracket by a bolt. The power unit includes a pedal crank shaft and a motor that produces auxiliary power, and outputs each of human power applied to the pedal crank shaft and a driving force of the motor, or a resultant force of the human power and the driving force of the motor. The bracket includes a front mounting seat and rear mounting seat pointing downward. The power unit includes first and second front mounts and first and second rear mounts which overlap the front mounting seat and rear mounting seat from below. The bolt extends in a direction in which the front mounting seat and rear mounting seat and the mounts overlap each other, and fastens the mounts to the front mounting seat and the rear mounting seat.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of priority to Japanese Patent Application 2015-196588 filed Oct. 2, 2015, the entire contents of which are hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a power-assisted bicycle including a power unit mounted on a body frame.

2. Description of the Related Art

A conventional power-assisted bicycle is disclosed in, e.g., Japanese Patent Laid-Open No. 2001-106163 (simply referred to as JP 2001-106163 hereinafter). This power-assisted bicycle includes a body frame that supports a front wheel and rear wheel, and a power unit mounted on the body frame. The power unit includes, for example, a pedal crank shaft which is rotated by the pedal force of a biker, a motor, and an output shaft. The resultant force of the pedal force (human power) of a biker and a motor driving force proportional to the magnitude of the pedal force is applied to the output shaft. The rotation of the output shaft is transmitted to the rear wheel via a chain.

The body frame includes, e.g., a head pipe which steerably supports a front fork, a down tube which extends rearward and downward from the head pipe, and a seat tube which extends upward from the lower end of the down tube. The power unit is mounted on a connector between the down tube and the seat tube via a plurality of power unit mounting brackets. A battery is installed above the power unit. The battery supplies power to the motor of the power unit. The battery has a shape which is elongated in an upper-lower direction and arranged between the seat tube and rear wheel.

The power unit mounting brackets are arranged in positions corresponding to the two ends of the power unit in the front-rear direction of the body frame, and in a position corresponding to the upper end of the power unit. Also, the pair of brackets each include plate-shaped portions extending in the left-right direction of the body frame. Each plate-shaped portion extends in the front-rear direction and in the upper-lower direction of the body frame, and includes a through hole to insert a fixing bolt. In addition, the plate-shaped portions are spaced apart from each other at an interval into which a mount of the power unit is inserted. The mount of the power unit includes a through hole to insert the fixing bolt, and is fastened to the plate-shaped portions by the fixing bolt while being inserted between the pair of plate-shaped portions. Therefore, the pair of plate-shaped portions elastically deform as they are pressed by the head of the fixing bolt and a nut, and are in tight contact with the mount as they are pushed from the two sides in the left-right direction.

In bicycles, including a power-assisted bicycle, the pedal force of a biker is desirably fully transmitted to the rear wheel.

To fully transmit the pedal force to the rear wheel in the power-assisted bicycle, the power unit must be mounted on the body frame in a rigid state in which the power unit cannot be displaced. To eliminate the displacement of the power unit, the rigidity of the power unit mounting brackets must be increased.

Unfortunately, the mounting structure of the power unit disclosed in JP 2001-106163 has the problem that the rigidity of the bracket that supports the power unit cannot further be increased. This is because, if the rigidity of the bracket increases, the plate-shaped portion hardly elastically deforms, so the pair of plate-shaped portions cannot clamp the mount of the power unit. When the plate-shaped portions and mount are made with high accuracy and the gap between them is minimized, the plate-shaped portions clamp the mount even if the elastic deformation amount of each plate-shaped portion is very small. However, this arrangement, which increases the accuracy more than necessary, cannot be used because the manufacturing cost unnecessarily increases.

SUMMARY OF THE INVENTION

Preferred embodiments of the present invention provide a power-assisted bicycle that improves fastening properties when mounting a power unit and increases the rigidity of the mounting structure, while reducing the manufacturing cost.

A power-assisted bicycle according to a preferred embodiment of present invention includes a front wheel, a rear wheel, a body frame that steerably and rotatably supports the front wheel, and rotatably supports the rear wheel, a power unit mounting bracket on the body frame, a power unit fixed to the bracket by a fixing bolt and including a crank shaft to be rotated by human power and a motor that produces auxiliary power, and that outputs each of the human power applied to the crank shaft and a motor driving force, or a resultant force of the human power and the motor driving force, and a transmission that transmits the resultant force of the human power and the motor driving force to the rear wheel, wherein the bracket includes a mounting seat pointing downward when viewed in a state in which the front wheel and the rear wheel are on the ground, the power unit includes a mount that overlaps the mounting seat from below, and the fixing bolt extends in a direction in which the mounting seat and the mount overlap each other, and fastens the mount to the mounting seat.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

First Preferred Embodiment

A first preferred embodiment of a power-assisted bicycle will be explained in detail below with reference toFIGS. 1 to 5.

A power-assisted bicycle1shown inFIG. 1includes a saddle2on which a biker (not shown) sits, and a handle3which the biker holds. When the biker steps on pedals4positioned below the saddle2, a rear wheel5is driven, and the bicycle runs. The saddle2is installed on the upper end of a seat tube7of a body frame6. The handle3is pivotally supported together with a front fork8by a head pipe9of the body frame6such that the handle3pivots together with the front fork8. The front fork8rotatably supports a front wheel10.

The body frame6includes, e.g., the head pipe9, a down tube11extending rearward and downward from the head pipe9, the seat tube7extending upward from a vicinity of the lower end of the down tube11, and chain stays12and seat stays13which rotatably support the rear wheel5. In the present preferred embodiment, a power unit mounting bracket14(to be described below) is, for example, welded to a lower end11aof the down tube11and a lower end7aof the seat tube7. A power unit15is mounted via the bracket14. A pedal crank shaft16(seeFIG. 2) of the power unit15supports the pedals4described above via pedal cranks17.

The chain stays12and seat stays13extend in the front-rear direction of the body frame on the two sides of the rear wheel5. Front ends12aof the chain stays12are, for example, welded to the power unit mounting bracket14(to be described later). The front ends of the seat stays13are welded to the upper end of the seat tube7. A battery18that supplies power to the power unit15and other electrical components is arranged in a space below the front ends of the seat stays13and between the rear wheel5and the seat tube7.

The battery18preferably has a rectangular or substantially rectangular shape which is elongated in an upper-lower direction. The lower end of the battery18is detachably supported by a support19. The support19is attached to the power unit mounting bracket14. The battery18supported by the support19is able to swing between a mounted position shown inFIG. 1and a detaching position at which the upper portion of the battery18falls to the left side of the body frame. In a state in which the battery18is positioned in the mounted position, a connector (not shown) is connected to the battery18, so the battery18is able to supply power. In a state in which the battery18is positioned in the detaching position, the connector is disconnected, so the battery18is able to be detached. Also, in the state in which the battery18is positioned in the above-described mounted position, a lock20attached to the seat tube7regulates the swinging of the battery18, thus holding the battery18.

As will be described in detail below, the power unit mounting bracket14and the power unit15are connected to each other, as shown inFIG. 2, by a front fastener21positioned at the ends of these members on the front side of the body frame, and a rear fastener22positioned at the ends on the rear side of the body frame.

The power unit15is assembled by attaching all of these components and devices to a metal housing23, and is arranged below and near the bracket14.

As shown in a bottom view ofFIG. 3, the housing23is able to be split in the left-right direction into a left half23apositioned on the body frame left side (the lower side inFIG. 3), and a right half23bpositioned on the body frame right side (the upper side inFIG. 3). The left half23aand the right half23bare joined together and connected by, for example, a plurality of connecting bolts24(seeFIG. 2).

The pedal crank shaft16extends in the left-right direction of the body frame through the end of the housing23on the body frame front side.

The pedal crank shaft16is rotatably supported by the housing23. One end of each pedal crank17is fixed to a corresponding one of the two ends of the pedal crank shaft16. The pedal4is rotatably attached to the other end of each pedal crank17. Referring toFIG. 3, a crank rotation output shaft25is exposed between the pedal crank17positioned on the body frame right side and the housing23. The crank rotation output shaft25is arranged on the same axis as that of the pedal crank shaft16, and is rotatably supported by the housing23. A chain sprocket26is attached to the crank rotation output shaft25. The crank rotation output shaft25is connected to a crank rotation input shaft28(to be described below) via a human-powered one-way clutch27. The one-way clutch27prevents the reverse rotation of the chain sprocket26when the pedal crank shaft16reversely rotates. Also, the one-way clutch27allows the chain sprocket26to rotate in the rotational direction when the bicycle runs in a state in which the pedal crank shaft16stops.

The chain sprocket26transmits the human power to the rear wheel5. As shown inFIG. 1, a chain29(seeFIG. 1) that drives the rear wheel is wound around the chain sprocket26. As shown inFIGS. 1 and 2, the chain29is wound around the chain sprocket26and a sprocket32of the rear wheel5in a state in which the chain29is wound around an output sprocket30and a tension sprocket31of the power unit15. The output sprocket30is fixed to a motor output shaft33(to be described below) of the power unit15. The tension sprocket31is rotatably supported by a tension arm34which is able to swing in the power unit15. The spring force of a tension coil spring35biases the tension arm34in a direction in which the chain29is pulled.

As indicated by the broken lines inFIG. 3, the power unit15includes, for example, a pedal force detector41arranged coaxially around the pedal crank shaft16, a motor42that produces auxiliary power positioned closer to the body frame rear side than the pedal crank shaft16, and a speed reducer43that reduces the speed of the rotation of the motor42and transmits the rotation to the motor output shaft33. The pedal force detector41detects the magnitude of human power. As the pedal force detector41, it is possible to use, e.g., a well-known magnetostrictive detector. The magnetostrictive pedal force detector41includes, for example, the cylindrical crank rotation input shaft28arranged coaxially around the pedal crank shaft16, and a detection coil41aarranged around the crank rotation input shaft28. In this case, one end of the crank rotation input shaft28is connected to the pedal crank shaft16, and the other end thereof is connected to an input of the one-way clutch27. That is, when the pedal force of the biker is applied to the pedal crank shaft16, the crank rotation input shaft28strains due to this pedal force. The detection coil41adetects a change in magnetic permeability due to a strain in the crank rotation input shaft28.

The motor42applies, to the speed reducer43, a motor driving force proportional to the magnitude of the human power detected by the pedal force detector41. The battery18positioned above the power unit15supplies electric power to the motor42.

The speed reducer43reduces the speed of the rotation of the motor42and transmits the rotation to the motor output shaft33. The motor output shaft33is connected to the speed reducer43via a motor one-way clutch (not shown). The motor one-way clutch allows the motor output shaft33to rotate together with the output sprocket30and chain29while the motor42is stopped.

In the power unit15, the motor output shaft33rotates when the motor42rotates, and the output sprocket30on the motor output shaft33applies the motor driving force to the chain29. That is, the power unit15outputs the human power applied to the pedal crank shaft16and the motor driving force to the outside. The human power and the motor driving force are applied to the chain29, and transmitted as the resultant force of the human power and motor driving force to the rear wheel5via the chain29. In the present preferred embodiment, the chain29is an example of “a transmission.”

As shown inFIG. 4, the bracket14that mounts the power unit15on the body frame6preferably has an arcuate shape which projects upward when viewed from the side.FIG. 4shows a state in which the power-assisted bicycle1with the front wheel10and rear wheel5on the ground is viewed from the right side of the body frame.

The bracket14according to the present preferred embodiment includes a first pipe44, a second pipe45, and a molded portion46. The first and second pipes44and45are made of, for example, an aluminum alloy, and are, for example, welded to the upper end of the molded portion46so as to extend in the left-right direction of the body frame.

The molded portion46is made to have a predetermined shape by, for example, forging or casting using, for example, an aluminum alloy. As shown inFIGS. 5 to 8, the molded portion46includes a pair of side plates47and48positioned at the end of the body frame right side and the end of the body frame left side, a pillar member49extending between the front ends of the side plates47and48, and a top plate50connecting the upper ends of the pair of side plates47and48.

Of the first and second pipes44and45, the first pipe44positioned on the body frame front side connects the upper ends of the pair of side plates47and48on the body frame front side.

The top plate50is located closer to the body frame rear side than the first pipe44. As shown inFIG. 2, the lower end11aof the down tube11and the lower end7aof the seat tube7are, for example, welded to the first pipe44. The lower end11aof the down tube11is also, for example, welded to the upper ends of the side plates47and48positioned closer to the body frame front side than the first pipe44. Of the first and second pipes44and45, the second pipe45positioned on the body frame rear side connects the upper ends of the pair of side plates47and48on the body frame rear side. As shown inFIG. 2, the front ends12aof the chain stays12are, for example, welded to the second pipe45. In the present preferred embodiment, therefore, the bracket14is fixed to the body frame6by being welded to the lower end11aof the down tube11, the lower end7aof the seat tube7, and the front ends12aof the chain stays12.

As shown inFIG. 6, a through hole50ais provided in a portion of the top plate50of the molded portion46, which is positioned between the first pipe44and second pipe45. Although not shown, a cable, a brake wire, and the like that connect the battery18and the power unit15are inserted into the through hole50a. The support19for the battery18is attached to the portion of the top plate50, which is positioned between the first pipe44and the second pipe45.

As shown inFIG. 5, the pillar member49of the molded portion46defines the front fastener21together with first and second front mounts51and52(seeFIG. 4) and two fixing bolts53of the power unit15. Also, as shown inFIG. 7, a bracket rear end54, having a plate-shape defined by the rear ends of the pair of side plates47and48and the rear end of the top plate50, defines the rear fastener22together with first and second rear mounts55and56and two fixing bolts53of the power unit15.

The pillar member49includes a front mounting seat61pointing downward. The bracket rear end54includes a rear mounting seat62pointing downward. “Downward,” as used herein, means downward when viewed in a state in which the front wheel10and rear wheel5of the power-assisted bicycle1are grounded, and includes downward along the vertical direction, and obliquely downward inclining to at least one of the front-rear direction and left-right direction of the body frame with respect to the vertical direction.

Screw holes63into which the fixing bolts53are screwed are provided in each of the front mounting seat61and the rear mounting seat62. In the present preferred embodiment, the screw hole63is an example of “a female screw.”

As shown inFIG. 3, the first front mount51of the power unit15is preferably integral with the front end of the left half23aof the housing23. The second front mount52is preferably integral with the front end of the right half23bof the housing23. Also, the first rear mount55is preferably integral with the rear end of the left half23aof the housing23. The second rear mount56is preferably integral with the rear end of the right half23bof the housing23. A through hole64(seeFIGS. 5 and 7) which extends in an upper-lower direction in a state in which the front wheel10and rear wheel5of the power-assisted bicycle are grounded is provided in each of the first and second front mounts51and52and the first and second rear mounts55and56.

As shown inFIG. 5, the first and second front mounts51and52are overlaid on the front mounting seat61of the pillar member49from below, and fastened by the fixing bolts53. The fixing bolts53extend in the upper-lower direction such that heads53aare positioned below. The fixing bolts53are inserted into the through holes64of the first and second front mounts51and52, and screwed into the screw holes63of the pillar member49. “The upper-lower direction” includes a direction that is vertical, i.e., a direction that is perpendicular to a horizontal plane, and directions that are inclined with respect to a horizontal plane. The first and second front mounting portions51and52and the front mounting seat61of the pillar member49overlap each other in the upper-lower direction.

As shown inFIG. 7, the first and second rear mounts55and56are overlaid on the rear mounting seat62of the bracket rear end54from below, and fastened by the fixing bolts53. The fixing bolts53extend in the upper-lower direction such that the heads53aare positioned below. The fixing bolts53are inserted into the through holes64of the first and second rear mounts55and56, and screwed into the screw holes63of the bracket rear end54. The first and second rear mounts55and56and the rear mounting seat62of the bracket rear end54overlap each other in an upper-lower direction.

Next, the procedure of mounting the power unit15described above on the body frame6will be explained. The work of mounting the power unit15is performed in a state in which the body frame6is inverted, i.e., turned upside down. When the body frame6is inverted, the front mounting seat61and rear mounting seat62of the bracket14point upward. To mount the power unit15on the body frame6, the first and second front mounts51and52are first overlaid on the front mounting seat61projecting upward, and the first and second mounts55and56are overlaid on the rear mounting seat62from above.

Then, the fixing bolts53are inserted from above into the through holes64of the mounts51,52,55, and56, and screwed into the screw holes63of the front mounting seat61and the rear mounting seat62. When the fixing bolts53are screwed into the screw holes63, the first and second front mounts51and52are fastened to the front mounting seat61, and the first and second rear mounts55and56are fastened to the rear mounting seat62. Consequently, the power unit15is mounted on the body frame6via the bracket14.

In the present preferred embodiment, the bracket14need not elastically deform when attaching the first and second front mounts51and52and the first and second rear mounts55and56of the power unit15to the front mounting seat61and the rear mounting seat62of the bracket14. This means that the bracket14having a high rigidity is able to be used. The bracket14and the mounts51,52,55, and56of the power unit15need only have an accuracy by which they are able to overlap each other in an upper-lower direction. This accuracy is lower than that when inserting the mount between the pair of mounting plates so as to narrow the gap as in a conventional bicycle.

Accordingly, the accuracy does not need to be higher than necessary when making the power unit mounting bracket14and the first and second front mounts51and52and the first and second rear mounts55and56of the power unit15. The power unit15is securely mounted on the body frame6by the power unit mounting bracket14having a high rigidity. The present preferred embodiment is able to provide a power-assisted bicycle that improves both the fastening properties and the rigidity when mounting the power unit15while also reducing the manufacturing cost.

The screw holes63(female screws) into which the fixing bolts53are screwed are provided in the front mounting seat61and the rear mounting seat62of the bracket14. The through holes64which extend in an upper-lower direction when viewed in a state in which the front wheel10and rear wheel5are grounded are provided in the first and second front mounts51and52and the first and second rear mounts55and56of the power unit15. The fixing bolts53are screwed into the screw holes63through the through holes64.

In the present preferred embodiment, the heads53aof the fixing bolts53are positioned below the mounts51,52,55, and56. When compared to a case in which the fixing bolts53are inverted in an upper-lower direction, therefore, parts to be exposed below the mounts51,52,55, and56are minimized. This is because, if the distal ends of the fixing bolts53are positioned below the mounts51,52,55, and56, the distal ends of the fixing bolts53and nuts (not shown) fastened to the distal ends are exposed. Accordingly, the outer appearance of the power unit15is not spoiled by the fixing bolts53.

Also, in the present preferred embodiment, the screw holes63are provided in the front mounting seat61and the rear mounting seat62of the bracket14. Therefore, the fastening work is performed with the fixing bolts53pointing downward by turning the body frame6upside down. That is, the fixing bolts53are inserted from above into the through holes64of the power unit15and screwed into the screw holes63.

Accordingly, the work of mounting the power unit15is easily performed in the present preferred embodiment.

The body frame6according to the present preferred embodiment includes the front fork8, the down tube11, the seat tube7, and the chain stays12. The bracket14is fixed to the body frame6by, for example, being welded to the lower end11aof the down tube11, the lower end7aof the seat tube7, and the front ends12aof the chain stays12.

The fasteners (the front fastener21and the rear fastener22) including the front mounting seat61and the rear mounting seat62of the bracket14, the mounts51,52,55, and56of the power unit15, and the fixing bolts53are provided in the two ends of the bracket14and power unit15in the front-rear direction of the body frame.

Since no fastener is provided in a central portion above the power unit15in the front-rear direction, the bracket14is close to the portion above the power unit15, so a wide free space is provided above the bracket14. In the present preferred embodiment, the support19of the battery18is arranged in this free space. Accordingly, the battery18, which is a heavy component, is arranged near the center of the lower portion of the body frame. This makes it possible to centralize the mass and lower the center of gravity, and further increases the running stability.

Furthermore, the bracket14according to the present preferred embodiment extends to the front portions of the chain stays12from the lower end11aof the down tube11via the lower portion of the seat tube7, and preferably has an arcuate shape extending in the front-rear direction of the body frame. Since the power unit15is mounted on the front end and the rear end of the bracket14, the power unit15reinforces the bracket14which extends in the front-rear direction. In the present preferred embodiment, therefore, it is unnecessary to provide a reinforcing member in the lower portion of the bracket14which projects upward when viewed from the side, so the bracket14is light in weight and compact.

Second Preferred Embodiment

A power-assisted bicycle according to a second preferred embodiment of present invention is shown inFIGS. 9 to 12. The same reference numerals as inFIGS. 1 to 8denote the same or similar members inFIGS. 9 to 12, and a detailed explanation thereof will be omitted.

A power-assisted bicycle71shown inFIG. 9differs from the power-assisted bicycle1shown inFIG. 1in the structure of a body frame6and the structure of a power unit15. The body frame6of the power-assisted bicycle71according to the present preferred embodiment includes a top tube72connecting a head pipe9and the upper end of a seat tube7. A front fork8preferably includes so-called telescopic front suspensions73. Also, a down tube11extends linearly rearward and downward. A battery18is detachably mounted on the down tube11. A lower end11aof the down tube11and a lower end7aof the seat tube7are individually welded, for example, to a power unit mounting bracket74.

The bracket74according to the present preferred embodiment has a predetermined shape formed by, for example, forging or casting using, for example, an aluminum alloy. The bracket74includes a pair of left and right side plates75and76, and a top plate77connecting the upper ends of the side plates75and76. As shown inFIG. 10, the bracket74preferably has an arcuate shape which projects upward when viewed from the side. As shown inFIG. 10, the lower end11aof the down tube11is, for example, welded as it obliquely downwardly abuts against the front portion of the top plate77from the front. The lower end7aof the seat tube7is, for example, welded as it obliquely downwardly abuts against the middle portion of the top plate77from behind. Front ends12aof chain stays12are, for example, welded as they abut against the rear portion of the top plate77from behind.

A bracket front end78including the front ends of the pair of left and right side plates75and76and the front end of the top plate77includes a front mounting seat61pointing downward. Also, a bracket rear end79including the rear ends of the pair of left and right side plates75and76and the rear end of the top plate77includes a rear mounting seat62pointing downward. As in the first preferred embodiment, “downward,” as used herein, means downward when viewed in a state in which a front wheel10and a rear wheel5of the power-assisted bicycle71are grounded. Also, “downward” includes downward along the vertical direction, and obliquely downward inclining to at least one of the front-rear direction and the left-right direction of the body frame with respect to the vertical direction.

As shown inFIG. 12, screw holes63are provided in the front mounting seat61and the rear mounting seat62. Fixing bolts53inserted into through holes64of the first and second rear mounts51and52of the power unit15are screwed into the screw holes63of the front mounting seat61. Fixing bolts53inserted into through holes64of the first and second rear mounts55and56are screwed into the screw holes63of the rear mounting seat62.

As shown inFIG. 11, the power unit15according to the present preferred embodiment includes a cylindrical resultant force output shaft80into which a pedal crank shaft16is inserted. A chain sprocket26is fixed to the end of the resultant force output shaft80on the right side of the body frame. The end of the resultant force output shaft80on the left side of the body frame is connected to a crank rotation input shaft28via an input one-way clutch27. A pedal force detector41according to the present preferred embodiment preferably includes a well-known magnetostrictive detector which detects, by a detecting coil41a, a change in magnetic permeability when the crank rotation input shaft28strains due to the pedal force of the biker.

A speed reducer43according to the present preferred embodiment reduces the speed of the rotation of a motor42, and transmits the rotation to the resultant force output shaft80via a motor one-way clutch (not shown). That is, the power unit15outputs the resultant force of human power applied to the pedal crank shaft16and the motor driving force to the outside via the resultant force output shaft80. The resultant force of the human power and the motor driving force is transmitted from the resultant force output shaft80to the rear wheel5via the chain sprocket26and a chain29. In the present preferred embodiment, the resultant force output shaft80, chain sprocket26, chain29, and the like are an example of “a transmission.”

In the present preferred embodiment, the same effects as that of the first preferred embodiment shown inFIGS. 1 to 8are obtained.

Third Preferred Embodiment

A mounting structure for mounting a power unit on a body frame according to a third preferred embodiment of the present invention may be configured as shown inFIGS. 13 to 15. The same reference numerals as inFIGS. 1 to 12denote the same or similar members inFIGS. 13 and 15, and a detailed explanation thereof will be omitted.

A power unit mounting bracket81according to the present preferred embodiment is preferably the same as the bracket74disclosed in the second preferred embodiment except that a first connector82(to be described below) is provided in the rear end.

The bracket81and a power unit15are connected to each other by a front fastener21including a front mounting seat61provided in the front end of the bracket81, and a rear fastener83including the first connector82provided in the rear end of the bracket81. As in the first and second preferred embodiments, the front fastener21includes the front mounting seat61of a bracket front end84, first and second front mounts51and52of the power unit15, and fixing bolts53.

As shown inFIG. 15, the rear fastener83according to the present preferred embodiment includes the first connector82in the rear end of the bracket81, a second connector85in the rear end of the power unit15, and a fastening bolt86extending through the first and second connectors82and85. The first connector82is preferably integral with a side plate75of the bracket81on the left side of the body frame. A through hole87extending in the left-right direction of the body frame is provided in the first connector82.

The second connector85is preferably integral with a left half23aof a housing23. The position of the second connector85overlaps the first connector82in the left-right direction of the body frame, and corresponds to a central portion of the bracket81in the left-right direction when viewed from the rear of the body frame. The second connector85according to the present preferred embodiment preferably overlaps the end surface of the first connector82on the body frame right side. Also, a through hole88communicating with the through hole87of the first connector82when the second connector85overlaps the first connector82is provided in the second connector85.

The fastening bolt86is inserted from the body frame right side into the through holes87and88of the first and second connectors82and85in a state in which the first and second connectors82and85overlap each other in the left-right direction of the body frame. A nut89is screwed on the distal end of the fastening bolt86, which is positioned on the body frame left side. The first connector82and the second connector85are thus fastened to each other by the fastening bolt86extending in the left-right direction of the body frame.

In the present preferred embodiment, the work of mounting the power unit15on a body frame6is performed by turning the body frame6upside down, as in the above-described first and second preferred embodiments. When the body frame6is turned upside down, the front mounting seat61of the bracket81points upward. To mount the power unit15on the bracket81, the power unit15is first placed on the bracket81, and the first connector82and the second connector85are connected by the fastening bolt86. In this state, the nut89is loosely screwed on the fastening bolt86. This allows the power unit15to swing in an upper-lower direction around the fastening bolt86as an axis.

Then, as shown inFIG. 16, a worker (not shown) pulls up the front end of the power unit15, thus rotating the power unit15around the fastening bolt86as an axis. When the front end of the power unit15is pulled up, a space S is provided between the lower portion of the power unit15in this state (this portion is the upper portion when viewed in a state in which a front wheel10and a rear wheel5are grounded) and the bracket81. Subsequently, the power unit15is held in the pulled-up state by using a jig (not shown) or the like, and the worker connects a connector91of the body frame and a connector92of the power unit15in the above-described space S. After this work of connecting the connectors91and92is complete, the power unit15is moved down to overlay the first and second front mounts51and52on the front mounting seat61of the bracket81from above. After that, the first and second front mounts51and52are fastened to the front mounting seat61by the fixing bolts53, and the second connector85is fastened to the first connector82by the fastening bolt86. The power unit15is fixed to the bracket81by thus fastening the fixing bolts53and the fastening bolt86.

In the present preferred embodiment, the power unit15is swingable around the fastening bolt86as an axis when assembled. Therefore, the connecting work is performed as described above by providing a wide open space between the lower portion of the power unit15(that is, the upper portion when the front wheel10and rear wheel5are grounded) and the bracket81. Accordingly, the present preferred embodiment is able to provide a power-assisted bicycle which further facilitates the work of assembling the power unit15.

Fourth Preferred Embodiment

A power-assisted bicycle according to a fourth preferred embodiment of the present invention is shown inFIG. 17. The same reference numerals as inFIGS. 1 to 16denote the same or similar members inFIG. 17, and a detailed explanation thereof will be omitted.

As will be described in detail below, a power-assisted bicycle101shown inFIG. 17includes a rear wheel suspension102. A power unit mounting bracket103according to the present preferred embodiment includes the bracket74disclosed in the second preferred embodiment. The bracket103is, for example, welded to a lower end11aof a down tube11and a lower end7aof a seat tube7. In the present preferred embodiment including the rear wheel suspension102, chain stays12function as swing arms104. Front ends12aof the chain stays12are not welded to the bracket103.

The front ends12aof the chain stays12shown inFIG. 17are connected to the lower end7aof the seat tube7by a first spindle105so as to be swingable in an upper-lower direction.

Seat stays13shown inFIG. 17swing together with the chain stays12, and front ends13aof the seat stays13are pivotally connected to the rear end of a link106by a second spindle107. The seat stays13function as the swing arms104together with the chain stays12. The link106includes a pair of left and right link pieces sandwiching the seat tube7from the two sides. A central portion of the link106in the front-rear direction is pivotally connected to the upper portion of the lower end7aof the seat tube7by a third spindle108. The upper end of a cushion unit111is pivotally connected to the front end of the link106by a fourth spindle110. The front surface of the lower end7aof the seat tube7is recessed rearward to define a recessed shape. The lower end of the cushion unit111is inserted into an internal recessed space of this recessed shape. The lower end of the cushion unit111is pivotally connected to the first spindle105. The axes of the first to fourth spindles105,107,108, and110are parallel or substantially parallel to the left-right direction of the body frame.

The bracket103and a power unit15according to the present preferred embodiment are connected to each other by a front fastener21and a rear fastener22. Like the above-described preferred embodiments, therefore, no fastener is provided above the power unit15, so the bracket103is arranged above and close the power unit15. This creates a wide-open space above the bracket103.

Also, a rear wheel5of the power-assisted bicycle101according to the present preferred embodiment is supported by a body frame6so as to be movable in an upper-lower direction by the rear wheel suspension102including the link106and the cushion unit111. The lower portion of the cushion unit111is arranged in the free space above the bracket103.

In the present preferred embodiment, therefore, the degree of freedom of the position of the cushion unit111increases, so the rear wheel suspension102having a high performance is able to be installed.

Modifications of Fasteners of the First to Fourth Preferred Embodiments

In each of the above-described preferred embodiments, female screws into which the fixing bolts53are screwed preferably are provided as the screw holes63in the brackets14,74,81, and103. However, the structure of the female screw may appropriately be changed as shown inFIGS. 18 to 20. The same reference numerals as inFIGS. 1 to 17denote the same or similar members inFIGS. 18 to 20, and a detailed explanation thereof will be omitted. InFIGS. 18 to 20, the brackets14,74,81, and103will generally be referred to as a bracket121.

Also, inFIGS. 18 to 20, the first and second front mounts51and52and the first and second rear mounts55and56will generally be referred to as a mount122. Furthermore, inFIGS. 18 to 20, the front mounting seat61of the pillar member49, the front mounting seat61of the bracket front ends78and84, and the rear mounting seat62of the bracket rear ends54and79will generally be referred to as a mounting seat123.

The screw hole63is provided in the mount122of the power unit15shown inFIG. 18. Also, a through hole124to insert the fixing bolt53is provided in the mounting seat123of the bracket121shown in each ofFIGS. 18 to 20. The fixing bolt53shown inFIG. 18is screwed into the screw hole63of the mount122through the through hole124of the bracket121.

A through hole125to insert the fixing bolt53is provided in the mount122shown in each ofFIGS. 19 and 20. The fixing bolt53shown inFIG. 19is inserted into the through holes124and125from below. “Below,” as used herein, means below when viewed in a state in which the front wheel10and rear wheel5are grounded. A nut126is screwed on the distal end (upper end) of the fixing bolt53. The fixing bolt53shown inFIG. 20is inserted into the through holes124and125from above. A nut126is screwed on the distal end (lower end) of the fixing bolt53. The nut126shown in each ofFIGS. 19 and 20is provided as a member separate from the bracket121and the mount122. The nut126shown inFIG. 19may be, for example, welded to the bracket121beforehand. The nut126shown inFIG. 20may be welded to the mount122beforehand.

In each ofFIGS. 19 and 20, the nut126, which is a member separate from one of the mounting seat123of the bracket121and the mount122of the power unit15, is an example of “a female screw.” In the present preferred embodiment, the mount122is able to be fastened to the mounting seat123by the fixing bolt53and the nut126without providing the screw hole63in the mount122or mounting seat123. Accordingly, both the mounting seat123and the mount122have simple shapes, so the rigidity of these members is further increased.

In preferred embodiments of the present invention described above, the mount of the power unit is pushed against the mounting seat of the bracket by fastening the fixing bolt. Therefore, the bracket need not elastically deform when mounting the mount of the power unit on the mounting seat of the bracket, so a bracket having a high rigidity is provided. The bracket and the mount of the power unit need only be made with an accuracy by which they are able to overlap each other in an upper-lower direction. This accuracy is lower than that when inserting a mount between a pair of mounting plates so as to narrow the gap.

Accordingly, the power unit mounting bracket and the mount of the power unit need not be made with an accuracy higher than necessary, and the power unit is securely mounted on the body frame by using a high-rigidity power unit mounting bracket. Therefore, preferred embodiments of the present invention provide a power-assisted bicycle that improves both the fastening properties when mounting the power unit and the rigidity of the mounting structure, while also reducing the manufacturing cost.