Electric assist bicycle

Provided is an electric assist bicycle that can apply a sufficient auxiliary driving force with a satisfactory gear change, preclude problems caused by interference between a mount or a battery and a front derailleur, and prevent a reduction in torque transmission efficiency. A cylindrical human-power transmission member that receives a transmitted human driving force is disposed on the outer periphery of a crank shaft, and a combined-force transmission member that receives the combined force of a human driving force and an auxiliary driving force from a motor is disposed on the outer periphery of the crank shaft. The electric assist bicycle includes a speed reduction mechanism that has pairs of reduction gears and a selection clutch engageable with the reduction gears, combines the human driving force and the auxiliary driving force, and changes gears for the combined force of the human driving force and the auxiliary driving force.

TECHNICAL FIELD

The present invention relates to an electric assist bicycle capable of traveling with a combination of a human driving force generated by a pedal force from a pedal and an auxiliary driving force generated by a motor.

BACKGROUND ART

In a known electric assist bicycle including a motor, power is fed from a power storage such as a battery, a human driving force, which includes a pedal force applied to a pedal, is detected by a torque sensor, and an auxiliary driving force (assisting force) of the motor is added according to the human driving force. Thus, such an electric assist bicycle can smoothly travel on an uphill or the like.

In such an electric assist bicycle, a motor drive unit including the motor is disposed at a crank shaft. Moreover, the electric assist bicycle configured thus has a relatively heavy motor drive unit that is disposed at a low position at the center of the electric assist bicycle (that is, the intermediate point between the front wheel and the rear wheel) in the longitudinal direction thereof. Thus, the front and rear wheels of the electric assist bicycle configured thus can be more easily lifted than an electric assist bicycle having a motor in the hub of the front or rear wheel. Such an electric assist bicycle can easily pass over a step of a path, achieving ease of handling and high riding stability.

Motor drive units to be provided in such an electric assist bicycle are broadly classified into a so-called double-shaft motor drive unit100that includes, as shown inFIG. 14, an auxiliary-driving force output sprocket103that outputs an auxiliary driving force from a motor in addition to a driving sprocket (also called a front sprocket or a chain sprocket)102serving as a human driving force output wheel disposed near one end of a crank shaft101, and a so-called single-shaft motor drive unit200, as shown inFIGS. 15 and 16, in which a human driving force generated by a pedal force and an auxiliary driving force generated by a motor are combined in the motor drive unit200and the combined force is outputted from a driving sprocket201.

The double-shaft motor drive unit100is disclosed in, for example, Patent Literature 1. As shown inFIG. 14, the auxiliary-driving force output sprocket103protrudes to the outside of a unit case104of the motor drive unit100from a portion behind the driving sprocket102in the motor drive unit100. The driving sprocket102that outputs a human driving force and the auxiliary-driving force output sprocket103that outputs an auxiliary driving force are engaged with a chain105serving as an endless driving force transmission member. The human driving force and the auxiliary driving force are combined by the chain105and then the combined force is transmitted to the rear wheel.

Further behind the auxiliary-driving force output sprocket103, a tensioner device (also called a guide device)106is provided in engagement with the chain105, which has been engaged with the auxiliary-driving force output sprocket103, so as to guide the chain105downward. Moreover, a tension sprocket107provided in the tensioner device106increases the winding angle of the chain105engaged with the auxiliary-driving force output sprocket103.

Meanwhile, the so-called single-shaft motor drive unit200is disclosed in, for example, Patent Literature 2. As shown inFIGS. 15 and 16, the outer periphery of a crank shaft202that receives a human driving force transmitted from the pedal has a cylindrical human-power transmission member203that receives the human driving force transmitted by serration coupling and so on, and a combined force member205where the human driving force transmitted via the human-power transmission member203is combined with an auxiliary driving force from a motor204. Moreover, the human driving force from the human-power transmission member203is transmitted to the combined force member205via a one-way clutch206. A large-diameter gear205athat receives an auxiliary driving force from the motor204via a speed reduction mechanism207is formed on one end of the combined force member205, whereas the driving sprocket201is attached to another end of the combined force member205, the driving sprocket201serving as a driving force output wheel engaged with a chain208serving as an endless driving force transmission member. A combined force on the combined force member205is transmitted from the driving sprocket201to the rear wheel through the chain208.

As shown inFIGS. 15 and 16, the single-shaft motor drive unit200is configured such that only the driving sprocket201is engaged with the chain208and the combined force of a human driving force and an auxiliary driving force is transmitted to the chain208. In contrast, the double-shaft motor drive unit100needs to engage, as shown inFIG. 14, the driving sprocket102for transmitting a human driving force, the auxiliary-driving force output sprocket103for transmitting an auxiliary driving force, and the tension sprocket107with the chain105.

Thus, the area of the single-shaft motor drive unit200in side view (laterally projected area) can be advantageously smaller (can be made compact) than that of the double-shaft motor drive unit100by devising the layout of the motor204and the speed reduction mechanism207. A so-called front derailleur can be attached to the single-shaft motor drive unit200including the driving sprocket201with multiple stages. On the other hand in the double-shaft motor drive unit100, it is necessary to engage the driving sprocket102, the auxiliary-driving force output sprocket103, and the tension sprocket107with the chain105, leading to difficulty in attaching the front derailleur.

Moreover, the single-shaft motor drive unit200advantageously eliminates the need for providing the tensioner device106of the tension sprocket107or the like. Generally, braking devices used for electric assist bicycles include a rim brake, a band brake, and a roller brake that are operated with a brake lever attached to a handle bar as those of ordinary bicycles. Depending on the regions or the request of an operator, the attachment of a coaster brake to the rear wheel may be required. The coaster brake is operated by rotating the pedals opposite to a forward rotation direction. In this case, the pedals rotated in the opposite direction apply a tension that pulls the lower part of the chain forward. Thus, the double-shaft motor drive unit100needs a unique design for the tensioner device106, whereas the single-shaft motor drive unit200advantageously eliminates the need for such a unique design.

Typically, in the foregoing advantageous single-shaft motor drive unit200, a magneto-striction torque sensor209for detecting a human driving force is provided on the outer periphery of the human-power transmission member203, which receives a human driving force transmitted from the crank shaft202, and a portion opposed to the outer periphery. Specifically, a magneto-striction generation portion209bis formed on the outer periphery of the human-power transmission member203, and a coil209afor detecting a change of magnetism on the magneto-striction generation portion209bis disposed to oppose to the magneto-striction generation portion209b. When the right and left pedals are pressed, the crank shaft202is twisted by a pedal force (human driving force). Thus, the twisted state of the human-power transmission member203that receives a human driving force transmitted from the crank shaft202is detected by the torque sensor209.

If a front derailleur is attached to the single-shaft motor drive unit200, an external derailleur for a sport bicycle or the like may be provided on the side of the crank shaft. Specifically, a plurality of driving sprockets may be disposed in the location of the driving sprocket201shown inFIG. 16so as to be displaced from each other along the axial direction of the crank shaft202(also referred to as a vehicle width direction) and a front derailleur that moves the chain in the vehicle width direction may be provided near the driving sprockets.

CITATION LIST

Patent Literatures

SUMMARY OF INVENTION

Technical Problems

However, the foregoing single-shaft motor drive unit including the external derailleur may cause the following problems:

First, the driving sprockets are laterally disposed and the chain is switched among the driving sprockets. Thus, the chain needs to have smaller dimensions (small thickness) in the vehicle width direction than an ordinary chain. However, in such an electric assist bicycle, the combined force of a human driving force and an auxiliary driving force is applied to the chain. Thus, the chain having smaller dimensions (small thickness) in the vehicle width direction than the ordinary chain may have quite a short life expectancy, causing frequent replacement of components or an insufficient auxiliary driving force.

Generally, a front derailleur is provided diagonally above and behind the driving sprocket. A battery mount and a battery are disposed in this location of the electric assist bicycle and thus these components (the mount and the battery) may interfere with the front derailleur. This may lead to difficulty in satisfactorily arranging the components and the front derailleur.

Since the front derailleur is exposed to the outside, the front derailleur or an engaging portion between the chain and the front derailleur may come into contact with obstacles during traveling. This may cause damage or take off the chain, reducing reliability.

Furthermore, in such an electric assist bicycle, the combined force of a human driving force and an auxiliary driving force is applied to the chain. The front derailleur needs to be developed as a special front derailleur capable of switching in response to a large torque.

The external derailleur provided in the single-shaft motor drive unit may be replaced with a derailleur having a planet gear mechanism. In this case, the use of the planet gear mechanism may reduce torque transmission efficiency.

The present invention has been devised to solve the problems. An object of the present invention is to provide an electric assist bicycle that can prevent an increase in the frequency of replacement of components such as a chain with a satisfactory gear change, add a sufficient auxiliary driving force, prevent problems caused by interference between a mount or a battery and a front derailleur, eliminate the need for developing a special front derailleur, and prevent a reduction in torque transmission efficiency.

Solution to Problem

In order to solve the problems, the present invention is an electric assist bicycle including a motor drive unit with a motor disposed at the intermediate position between a front wheel and a rear wheel, the electric assist bicycle being capable of traveling with a combination of a human driving force generated by a pedal force from a pedal and an auxiliary driving force generated by the motor, the electric assist bicycle including a crank shaft that receives a human driving force transmitted from the pedal and rotates about a different axis from the motor, the crank shaft having a cylindrical human-power transmission member on the outer periphery of the crank shaft, the human-power transmission member receiving the transmitted human driving force, the crank shaft having a combined-force transmission member on the outer periphery of the crank shaft, the combined-force transmission member receiving a combined force of a human driving force and an auxiliary driving force from the motor, the electric assist bicycle including a speed reduction mechanism that has pairs of reduction gears and a selection clutch engageable with the reduction gears, combines the human driving force and the auxiliary driving force, and changes gears for the combined force of the human driving force and the auxiliary driving force, the motor drive unit containing the human-power transmission member, the combined-force transmission member, and the speed reduction mechanism, wherein the combined force transmitted to the combined-force transmission member through the speed reduction mechanism is transmitted to the rear wheel through a driving force output wheel coaxial with the crank shaft and an endless driving force transmission member looped over the human driving force output wheel.

With this configuration, the selection clutch of the speed reduction mechanism is engaged with selected one of the reduction gears. A combined force transmitted to the combined-force transmission member through the speed reduction mechanism is transmitted to the rear wheel through the driving force output wheel coaxial with the crank shaft and the endless driving force transmission member looped over the human driving force output wheel.

The speed reduction mechanism of the present invention includes a human-power transmitting reduction gear that is rotatably disposed on the outer periphery of the crank shaft and receives a transmitted human driving force, an intermediate shaft disposed in parallel with the crank shaft, a plurality of intermediate-shaft reduction gears provided on the intermediate shaft, a combined-force reduction gear rotatably provided in engagement with the intermediate reduction gear, and a selection clutch that is rotated integrally with the combined-force transmission member engaged with the selection clutch and is selectively engaged with one of the human-power transmitting reduction gear and the combined-force reduction gear.

With this configuration, the selection clutch is selectively engaged with the human-power transmitting reduction gear or the combined-force reduction gear. This can satisfactorily transmit a combined force to the rear wheel while changing gears. Moreover, the combined force of a human driving force and an auxiliary driving force is transmitted with the engagement of the intermediate-shaft reduction gears provided on the intermediate shaft, the human-power transmitting reduction gear rotatably provided on the outer periphery of the crank shaft, and the combined-force reduction gear rotatably provided on the combined-force transmission member. This can improve the transmission efficiency of a torque (force) as compared with the use of a planet gear mechanism.

According to the present invention, the human-power transmission member has the magneto-striction generation portion of a torque sensor for detecting the human driving force formed.

The electric assist bicycle may include a one-way clutch for interrupting an auxiliary driving force on the transmission path of a human driving force between the crank shaft and the human-power transmitting reduction gear, the one-way clutch preventing the transmission of an auxiliary driving force from the motor to the crank shaft. In this case, an interlocking cylindrical part may be disposed on the outer periphery of the crank shaft so as to be engaged with the human-power transmission member, and the one-way clutch for interrupting an auxiliary driving force may be disposed between the interlocking cylindrical part and the human-power transmitting reduction gear.

With this configuration, the interlocking cylindrical part is provided between the human-power transmission member and the human-power transmitting reduction gear. Also in the case where the magneto-striction generation portion of the torque sensor for detecting a human driving force is formed on the human-power transmission member, vibrations during the switching of the selection clutch and vibrations from the one-way clutch for interrupting an auxiliary driving force are hardly transmitted to the human-power transmission member. Thus, the torque sensor can be more reliable than in the absence of the interlocking cylindrical part.

The electric assist bicycle may further include a rotation detector that detects the rotation of the interlocking cylindrical part or the human-power transmission member. This configuration can detect the rotation of the interlocking cylindrical part or the human-power transmission member, that is, the rotation of the crank shaft.

A one-way clutch does not need to be provided on the transmission path of a human driving force between the crank shaft and the human-power transmitting reduction gear. In this case, the human-power transmission member and the human-power transmitting reduction gear are also rotated in response to the rotation of the crank shaft regardless of the rotation direction of the crank shaft and the human-power transmission member relative to the human-power transmitting reduction gear. Thus, also in the case where the hub of the rear wheel has, for example, a coaster brake that operates when the pedals are rotated opposite to a forward rotation direction, a reversed rotation of the crank shaft from a forward rotation is transmitted to the coaster brake. This can satisfactorily operate the coaster brake.

Advantageous Effects of Invention

According to the present invention, the speed reduction mechanism provided in the motor drive unit includes the pairs of reduction gears and the selection clutch engageable with the reduction gears. The speed reduction mechanism combines the human driving force and the auxiliary driving force and changes gears for the combined force of the human driving force and the auxiliary driving force. This eliminates the need for a chain having small dimensions (small thickness) relative to a vehicle width direction for providing an external derailleur in a single-shaft motor drive unit, thereby preventing a chain from having quite a short life expectancy that may cause frequent replacement of components or, an insufficient auxiliary driving force. Furthermore, the need for a front derailleur is eliminated and thus any problems do not arise as to the location of a front derailleur. Furthermore, the human-power transmission member, the combined-force transmission member, and the speed reduction mechanism are provided in the motor drive unit so as to be protected from the outside, achieving higher reliability.

The speed reduction mechanism includes the human-power transmitting reduction gear that is rotatably disposed on the outer periphery of the crank shaft and receives a transmitted human driving force, the intermediate shaft disposed in parallel with the crank shaft, the intermediate-shaft reduction gears provided on the intermediate shaft, the combined-force reduction gear rotatably provided on the combined-force transmission member into engagement with the intermediate reduction gear, and the selection clutch that is rotated integrally with the combined-force transmission member engaged with the selection clutch and is selectively engaged with the human-power transmitting reduction gear or the combined-force reduction gear. This can satisfactorily transmit a combined force to the rear wheel while changing gears. Moreover, a combined force can be outputted to the driving force output wheel of the driving sprocket or the like with higher torque (force) transmission efficiency than in the use of a planet gear mechanism.

DESCRIPTION OF EMBODIMENTS

An electric assist bicycle according to an embodiment of the present invention will be described below with reference to the accompanying drawings. In the following explanation, a lateral direction and a longitudinal direction are set relative to the traveling direction of a rider on an electric assist bicycle1. The present invention is not limited to the following configuration.

InFIGS. 1 and 2, reference numeral1denotes the electric assist bicycle according to the embodiment of the present invention. As shown inFIGS. 1 and 2, the electric assist bicycle1includes: a metallic frame2including a head tube2a, a front fork2b, a main tube2c, a seat tube2d, a chain stay2e, and a seat stay2f; a front wheel3rotatably attached to the lower end of the front fork2b; a rear wheel4rotatably attached to the rear end of the chain stay2e; a handle bar5that changes the direction of the front wheel3; a saddle6; a crank7and pedals8that receive a human driving force including a pedal force; a motor drive unit20including an electric motor21(FIG. 4) serving as a driving source for generating an auxiliary driving force (assist force) and a control unit24(FIG. 4) for electrically controlling the motor21and so on; a battery12including a secondary battery for supplying driving power to the motor21; a manual gear change part (not shown)18for setting the speed (first or second speed) of a gear changer (gear changing unit), which will be discussed later, the manual gear change part18being attached to the handle bar5or the like so as to be operated by a rider; a manual operation part (not shown) for switching the power supply of the electric assist bicycle1and setting a riding mode, the manual operation part being attached to the handle bar5or the like so as to be operated by a rider and so on; a driving sprocket (may be called a front sprocket, a crank sprocket, or a front gear)13that is attached so as to coaxially rotate with a crank shaft7aand serves as a driving force output wheel for outputting the combined force of a human driving force and an auxiliary driving force; a rear sprocket (may be called a rear gear)14serving as a rear wheel attached to a hub (also called a rear hub)9of the rear wheel4; a chain15serving as an endless driving force transmission member rotatably wound around the driving sprocket13and the rear sprocket14in an endless manner; and a chain cover17that laterally covers the chain15and so on. The battery12is an example of a power storage and is preferably a secondary battery. Another example of the power storage may be a capacitor. The crank7includes crank arms7bprovided on the right and left of the crank7and the crank shaft7aconnecting the right and left crank arms7b. The pedals8are rotatably attached to the ends of the crank arms7b.

As shown inFIGS. 1 and 2, also in the electric assist bicycle1, the motor drive unit20is disposed at the intermediate position between the front wheel3and the rear wheel4, for example, substantially behind the crank shaft7a(specifically, under the intermediate position). This configuration locates the relatively heavy motor drive unit20at the center of the electric assist bicycle1in the longitudinal direction. Thus, the front wheel3and the rear wheel4are easily lifted and the electric assist bicycle1can easily pass over a step of a path, achieving ease of handling of the body (e.g., the frame2) of the electric assist bicycle1and high riding stability.

FIGS. 3(a) and 3(b)are a right side view and a right-side cross section of the motor drive unit20.FIG. 4is a plane section showing the motor drive unit20.

As shown inFIGS. 3(a), 3(b), and4, the motor drive unit20includes a unit case22constituting a casing and so on. The unit case22includes a motor case22a, a left-side case22b, and a right-side case22c. The crank shaft7alaterally penetrates the front of the motor drive unit20. Moreover, the outer periphery of the crank shaft7ahas a substantially cylindrical human-power transmission member28that receives a human driving force transmitted from the crank shaft7a, an interlocking cylindrical part23that receives the human driving force transmitted from the human-power transmission member28, and a combined-force transmission member29that receives the human driving force from the interlocking cylindrical part23via, for example, a one-way clutch (a one-way clutch for interrupting an auxiliary driving force)30and transmits the combined force of the human driving force and an auxiliary driving force from the motor21to the driving sprocket13.

Furthermore, a speed reduction mechanism25having pairs of reduction gears36to41is longitudinally disposed from the right side of the front of the unit case22to the center of the unit case22. In the present embodiment, as will be discussed later, the function of an internal derailleur (internal gear changing unit) is also provided in the speed reduction mechanism25. Moreover, the motor21is disposed on the left side of the rear of the unit case22. The control unit24is disposed on the right side of the rear of the unit case22and includes a control printed circuit board24athat has electronic components for performing kinds of electrical control and a storage containing kinds of information.

The motor drive unit20will be more specifically described below. As shown in, for example,FIGS. 4, 5, and6, the crank shaft7alaterally penetrating the front of the motor drive unit20is rotatably disposed with bearings26and27. The cylindrical human-power transmission member28is fit onto the outer periphery of the left side of the crank shaft7avia a serration part (or spline part)7cso as to rotate as an integral part. Moreover, a serration part (or spline part)28bis also formed at a point corresponding to the serration part (or spline part)7cof the crank shaft7ainside the human-power transmission member28, and the serration part28bis engaged with the serration part (or spline part)7cof the crank shaft7a.

A magneto-striction generation portion31bhaving magnetic anisotropy is formed on the outer surface of the human-power transmission member28. Coils31aare disposed with a certain clearance (space) on the outer periphery of the magneto-striction generation portion. The magneto-striction generation portion31band the coils31aconstitute a magneto-striction torque sensor (human power detection part)31. With this configuration, a human driving force from the crank shaft7ais transmitted to the human-power transmission member28and is detected by the torque sensor31. In the magneto-striction torque sensor31, the magneto-striction generation portion31bis spirally formed with an angle of, for example, +45° to −45° with respect to the axial direction of the human-power transmission member28. When a human driving force is transmitted to the human-power transmission member28, the magneto-striction generation portion31bon the surface of the human-power transmission member28is distorted so as to vary between increased and decreased portions in magnetic permeability. Thus, a difference in the inductance of the coils31ais measured so as to detect the magnitude of the torque (human driving force).

The interlocking cylindrical part23is disposed next to the right side of the human-power transmission member28on the outer periphery of the crank shaft7aso as to rotate relative to the crank shaft7a. The interlocking cylindrical part23rotates integrally with the human-power transmission member28while being engaged at a serration part (or spline part)28aformed on the outer periphery of the right end of the human-power transmission member28and a serration part (or spline part)23aformed on the inner periphery of the left end of the interlocking cylindrical part23. In the present embodiment, the serration part (or spline part)23aformed on the inner periphery of the left end of the interlocking cylindrical part23is externally fit onto the serration part (or spline part)28aof the human-power transmission member28.

Furthermore, in the present embodiment, a rotation detecting member11for detecting the rotational state of the interlocking cylindrical part23is attached to the outer periphery of the left side of the interlocking cylindrical part23. Moreover, a rotation detector10is fixed to the unit case22so as to laterally hold the rotation detecting member11with a small clearance. For example, the rotation detector10includes a pair of optical sensors disposed along the rotation direction of the rotator11, the optical sensor including a light emitting part and a light receiving part. The rotator11has a large number of teeth (light-shielding portions) extending outward like comb teeth. The teeth of the rotator11pass between the light emitting part and the light receiving part of the rotation detector10, allowing the rotation detector10to electrically detect a light incidence state and a light shielding state. Subsequently, the amount and direction of rotation of the interlocking cylindrical part23are detected in the control unit24that receives the signal of the rotation detector10. The optical sensor may be replaced with a magnetometric sensor to detect the amount and direction of rotation of the interlocking cylindrical part23. In this case, the interlocking cylindrical part23rotates integrally with the human-power transmission member28while the human-power transmission member28rotates integrally with the crank shaft7a. The detection of the amount and direction of rotation of the interlocking cylindrical part23allows the detection of the amounts and directions of rotations of the crank shaft7aand the pedals8.

The human-power transmitting reduction gear (one of the reduction gears)36provided in the speed reduction mechanism25is disposed on the outer periphery of the right side of the interlocking cylindrical part23via the one-way clutch (one-way clutch for interrupting an auxiliary driving force)30. In riding forward with the pedals8, a human driving force transmitted to the interlocking cylindrical part23is transferred to the human-power transmitting reduction gear36of the speed reduction mechanism25.

As shown inFIG. 4, the motor21includes a rotating shaft21aand a rotor portion21bthat are rotatably supported by bearings32and33. The rotating shaft21aof the motor21protrudes to the right so as to form the motor-shaft reduction gear40, which will be discussed later, on the outer periphery of the protruding portion.

As shown inFIGS. 4 and 5, the speed reduction mechanism25includes the pairs of reduction gears36to41(three pairs in the present embodiment) including the human-power transmitting reduction gear36and a selection clutch45that can be engaged with the human-power transmitting reduction gear36and the combined-force reduction gear41, which will be discussed later. A human driving force transmitted through the crank shaft7aand an auxiliary driving force transmitted from the motor21are combined and the combined force thereof changes speeds by engaging the selection clutch45with selected one of the reduction gears36and41.

Specifically, the speed reduction mechanism25includes: the large-diameter human-power transmitting reduction gear36that is rotatably disposed on the outer periphery of the crank shaft7aso as to receive a transmitted human driving force; an intermediate shaft44that is laterally extended at the center of the motor drive unit20in the longitudinal direction and is rotatably supported by bearings34and35in parallel with the crank shaft7a; the first to third intermediate-shaft reduction gears37,38, and39provided on the intermediate shaft44; the small-diameter motor-shaft reduction gear40that is formed on the rotating shaft21aof the motor21and is engaged with the large-diameter first intermediate-shaft reduction gear37; the large-diameter combined-force reduction gear41that is rotatably provided on the combined-force transmission member29via a bearing43and is engaged with the small-diameter third intermediate reduction gear39; the selection clutch45that is integrally rotated in laterally movable engagement with the combined-force transmission member29via spline parts29aand45a(specifically, along the axial direction of the crank shaft7a) and is selectively engaged with the human-power transmitting reduction gear36or the combined-force reduction gear41; a clutch driving part46that is laterally movably engaged with a groove portion45bformed on the outer periphery of the selection clutch45so as to laterally move the selection clutch45selectively into engagement with the human-power transmitting reduction gear36or the combined-force reduction gear41; and a one-way clutch47for interrupting a human driving force, the one-way clutch47being disposed between the intermediate shaft44and the first intermediate-shaft reduction gear37so as to prevent the transmission of a human driving force from the human-power transmitting reduction gear36to the motor21. The rotating shaft21aof the motor21is also disposed in parallel with the crank shaft7alike the intermediate shaft44.

When the motor21is rotated in a predetermined direction to drive the electric assist bicycle1forward, the speed of rotation of the motor21(auxiliary driving force) is reduced (that is, the torque is increased) through an engaged portion between the small-diameter motor-shaft reduction gear40and the large-diameter first intermediate-shaft reduction gear37and then is transmitted to the intermediate shaft44. Subsequently, the speed of rotation is further reduced through an engaged portion between the small-diameter second intermediate-shaft reduction gear38and the large-diameter human-power transmitting reduction gear36and then the motor21rotates the human-power transmitting reduction gear36.

In the present embodiment, the second intermediate-shaft reduction gear38is integrally formed on the intermediate shaft44, whereas the third intermediate-shaft reduction gear39is fixed with a different component from the intermediate shaft44by press fitting or serration coupling so as to be integrally rotated with the intermediate shaft44. The third intermediate-shaft reduction gear39is slightly larger in diameter than the second intermediate-shaft reduction gear38. The combined-force reduction gear41engaged with the third intermediate-shaft reduction gear39is slightly smaller in diameter than the human-power transmitting reduction gear36engaged with the second intermediate-shaft reduction gear38. Thus, when the second intermediate-shaft reduction gear38and the third intermediate-shaft reduction gear39are integrally rotated with the intermediate shaft44, the combined-force reduction gear41rotates faster than the human-power transmitting reduction gear36.

The selection clutch45has teeth45cformed on the inner periphery of the left side of the selection clutch45, the teeth45cbeing engageable with teeth36aformed on the human-power transmitting reduction gear36. As shown inFIGS. 4 and 5, when the selection clutch45is placed on the left side, the teeth45cof the selection clutch45are engaged with the teeth36aof the human-power transmitting reduction gear36and the rotary force of the human-power transmitting reduction gear36is transmitted to the combined-force transmission member29through the selection clutch45. Moreover, a plurality of engaging protrusions45dare laterally formed from the right side of the selection clutch45so as to be engaged with a plurality of engaging holes41acircumferentially formed on the combined-force reduction gear41. As shown inFIG. 7, when the selection clutch45is located on the right side, the engaging protrusions45dof the selection clutch45are inserted into engagement with the engaging holes41aof the combined-force reduction gear41so as to transmit the rotary force of the combined-force reduction gear41to the combined-force transmission member29through the selection clutch45. If the selection clutch45is disposed at the intermediate position (not shown) between the left position inFIGS. 4 and 5and the right position inFIG. 7, the selection clutch45is not engaged with the human-power transmitting reduction gear36or the combined-force reduction gear41.

In the present embodiment, as schematically shown inFIGS. 3(b) and 6(b), the clutch driving part46for driving the selection clutch45holds the selection clutch45with a forked end so as to move along a guide rod48laterally extending in parallel with the crank shaft7a. The clutch driving part46is interlocked through a wire or the like with the manual gear change part18attached to the handle bar5and so on. An operation on the manual gear change part18laterally moves the selection clutch45through the clutch driving part46.

With this configuration, if the manual gear change part18is operated to a first speed, the selection clutch45is placed at the left position shownFIGS. 4 and 5, engaging the teeth45cof the selection clutch45with the teeth36aof the human-power transmitting reduction gear36.

In this state, a forward rotation of the pedal8transmits a human driving force from the pedal8to the human-power transmission member28through the crank shaft7aand then transmits the human driving force to the human-power transmitting reduction gear36through the interlocking cylindrical part23and the one-way clutch (one-way clutch for interrupting an auxiliary driving force)30. At this point, the torque sensor31detects the torque of the human driving force and then the motor21is driven to output an auxiliary driving force corresponding to the torque. Subsequently, a turning force from the motor21is transmitted to the human-power transmitting reduction gear36through the first intermediate-shaft reduction gear37, the one-way clutch (one-way clutch for interrupting a human driving force)47, the intermediate shaft44, and the second intermediate-shaft reduction gear38while the speed is reduced (the torque is increased). At this point, the combined-force reduction gear41engaged with the third intermediate-shaft reduction gear39is also rotated in response to the rotation of the intermediate shaft44but the combined-force reduction gear41is not engaged with the selection clutch45, and therefore simply runs idle.

An auxiliary driving force transmitted to the human-power transmitting reduction gear36is combined with a human driving force on the human-power transmitting reduction gear36. The combined force is transmitted to the selection clutch45through the teeth36aand45c, is transmitted to the combined-force transmission member29through the spline parts45aand29a, and then is transmitted to the rear wheel4through the chain15from the driving sprocket13attached to the combined-force transmission member29. This rotates the rear wheel4.

If the manual gear change part18is operated to a second speed, as shown inFIG. 7, the selection clutch45moves to the right position so as to separate the teeth45cof the selection clutch45from the teeth36aof the human-power transmitting reduction gear36. After that, the engaging protrusions45dof the selection clutch45are fit into engagement with the engaging holes41aof the combined-force reduction gear41.

In this state, as in the setting to the first speed, a forward rotation of the pedal8transmits a human driving force from the pedal8to the human-power transmitting reduction gear36through the crank shaft7a, the human-power transmission member28, the interlocking cylindrical part23, and the one-way clutch (one-way clutch for interrupting an auxiliary driving force)30and then transmits the human driving force to the intermediate shaft44from the human-power transmitting reduction gear36through the second intermediate-shaft reduction gear38. When the torque sensor31detects the torque of the human driving force and an auxiliary driving force corresponding to the torque is outputted from the motor21, a turning force from the motor21is transmitted to the intermediate shaft44through the first intermediate-shaft reduction gear37and the one-way clutch (one-way clutch for interrupting a human driving force)47. This combines the human driving force and the auxiliary driving force on the intermediate shaft44.

The combined force on the intermediate shaft44is transmitted to the combined-force reduction gear41through the third intermediate-shaft reduction gear39and then the engaging protrusions45dare fit into the engaging holes41aof the combined-force reduction gear41so as to engage the selection clutch45. This transmits the combined force to the selection clutch45. Moreover, the combined force is transmitted to the driving sprocket13through the combined-force transmission member29and then is transmitted from the driving sprocket13to the rear4through the chain15, rotating the rear wheel4. The turning force (combined force) of the combined-force reduction gear41that rotates faster than the human-power transmitting reduction gear36is transmitted to the combined-force transmission member29and the driving sprocket13. This rotates the driving sprocket13at the second speed higher than the first speed.

With this configuration, the selection clutch45is selectively engaged with the human-power transmitting reduction gear36or the combined-force reduction gear41. This can satisfactorily transmit the combined force to the rear wheel4while changing gears. Gears are changed for the combined force of a human driving force and an auxiliary driving force instead of only one of a human driving force and an auxiliary driving force. This can satisfactorily change gears for a combined force corresponding to a human driving force (a combined force substantially proportionate to a human driving force) using the motor21capable of outputting an auxiliary driving force that can be satisfactorily combined with a human driving force or the speed reduction mechanism25, achieving highly reliable riding.

According to the present embodiment of the present invention, the speed reduction mechanism25provided in the motor drive unit20constitutes the gear changing unit (gear changing mechanism) but a so-called external derailleur having multiple driving sprockets is not provided. This eliminates the need for a chain having small dimensions (a small thickness) relative to a vehicle width direction required for providing an external derailleur in a single-shaft motor drive unit, thereby preventing a chain from having quite a short life expectancy that may cause frequent replacement of components or an insufficient auxiliary driving force. Furthermore, the need for a front derailleur is eliminated and thus any problems do not arise as to the location of a front derailleur. The human-power transmission member28, the combined-force transmission member29, and the speed reduction mechanism25are provided in the motor drive unit20so as to be protected from the outside. Thus, these components are hardly damaged during traveling, keeping high reliability.

Moreover, the combined force of a human driving force and an auxiliary driving force is transmitted with the engagement of the intermediate-shaft reduction gears37,38, and39provided on the intermediate shaft44, the human-power transmitting reduction gear36rotatably provided on the outer periphery of the crank shaft7adisposed in parallel with the intermediate shaft44, and the combined-force reduction gear41rotatably provided on the combined-force transmission member29. This can advantageously improve the transmission efficiency of a torque (force) as compared with the use of a planet gear mechanism.

In this configuration, the one-way clutch30for interrupting an auxiliary driving force is provided on a transmission path for a human driving force between the crank shaft7aand the human-power transmitting reduction gear36, the one-way clutch30preventing the transmission of an auxiliary driving force from the motor21to the crank shaft7a. The one-way clutch30for interrupting an auxiliary driving force transmits a human driving force in a forward direction from the human-power transmission member28and the interlocking cylindrical part23to the human-power transmitting reduction gear36but does not transmit an auxiliary driving force in a forward direction from the intermediate shaft44and the human-power transmitting reduction gear36to the crank shaft7aand the pedals8through the interlocking cylindrical part23and the human-power transmission member28. In the electric assist bicycle1, even if a rider stops pressing the pedals8, so-called delay control is performed so as to keep the rotation of the motor21for a while. The one-way clutch30for interrupting an auxiliary driving force cuts the auxiliary driving force to prevent continuous rotations of the crank shaft7aand the pedals8by themselves, as a result, even if a rider stops pressing the pedals8, preventing continuous rotations of the crank shaft7aand the pedals8by themselves, thereby improving convenience.

With this configuration, the one-way clutch47for interrupting a human driving force is disposed between the intermediate shaft44and the first intermediate-shaft reduction gear37so as to prevent the transmission of a human driving force from the human-power transmitting reduction gear36to the motor21. Thus, if the battery12runs out and the pedals8are pressed without the output of an auxiliary driving force from the motor21, a human driving force rotates the intermediate shaft44and the second and third intermediate-shaft reduction gears38and39but does not rotate the first intermediate-shaft reduction gear37and the rotating shaft21aand the rotor portion21bof the motor21, preventing the application of an excessive force to the pedals8(a so-called drag resistance can be considerably reduced).

With this configuration, the interlocking cylindrical part23is provided between the human-power transmission member28and the human-power transmitting reduction gear29. Also in the case where the magneto-striction generation portion31bof the torque sensor31for detecting a human driving force is formed on the human-power transmission member28, vibrations during the switching of the selection clutch45and vibrations from the one-way clutch30for interrupting an auxiliary driving force are hardly transmitted to the human-power transmission member28. Thus, the torque sensor31is more reliable than in the absence of the interlocking cylindrical part23.

This configuration further includes the rotation detector10that detects the rotation of the interlocking cylindrical part23, thereby satisfactorily detecting the rotations of the interlocking cylindrical part23and the human-power transmission member28, that is, the rotation of the crank shaft7a. An optical sensor provided as the rotation detector10advantageously protects the torque sensor31from magnetism. The rotation detector10is not limited to an optical sensor and thus may be a magnetic sensor. Furthermore, a magnetic shield for blocking magnetism between the magnetic sensor and the torque sensor31may be provided.

In the present embodiment, the gear changing unit has a structure capable of switching between two speeds (two steps), specifically, a first speed and a second speed (so-called two-speed gear mechanism). The gear changing unit is not limited to this configuration and thus may switch among three or more speeds.

FIGS. 8 to 11show a motor drive unit50having a so-called three-speed gear structure according to another embodiment of the present invention. As shown inFIGS. 8 and 9, in addition to the configuration of the gear changing mechanism25in the motor drive unit20according to the foregoing embodiment, the motor drive unit50further includes the following constituent elements: a gear changing mechanism25in the motor drive unit50includes a fourth intermediate-shaft reduction gear52having a relatively small diameter provided on an intermediate shaft44, a large-diameter second combined-force reduction gear51that is rotatably provided on a combined-force transmission member29via a bearing55and is engaged with the small-diameter fourth intermediate reduction gear52, a selection clutch53that is integrally rotated in laterally movable engagement with the combined-force transmission member29via spline parts29band53a(specifically, along the axial direction of a crank shaft7a) and is selectively engaged with a combined-force reduction gear41(will be referred to as a first combined-force reduction gear41) or the second combined-force reduction gear51, and a clutch driving part54that is laterally movably engaged with a groove portion53bformed on the outer periphery of the selection clutch53so as to laterally move the selection clutch53selectively into engagement with the first combined-force reduction gear41or the second combined-force reduction gear51.

The fourth intermediate-shaft reduction gear52is slightly larger in diameter than a third intermediate-shaft reduction gear39and the second combined-force reduction gear51engaged with the fourth intermediate-shaft reduction gear52is slightly smaller in diameter than the first combined-force reduction gear41engaged with a third intermediate-shaft reduction gear38. Thus, when a human-power transmitting reduction gear36is rotated, the second intermediate-shaft reduction gear38engaged with the human-power transmitting reduction gear36is rotated, the third intermediate-shaft reduction gear39and the fourth intermediate-shaft reduction gear52rotate at the same rpm as the second intermediate-shaft reduction gear38via the intermediate shaft44having the second intermediate-shaft reduction gear38formed, and the first combined-force reduction gear41engaged with the third intermediate-shaft reduction gear39and the second combined-force reduction gear51engaged with the fourth intermediate-shaft reduction gear52rotate in synchronization with one another. At this point, the first combined-force reduction gear41rotates faster than the human-power transmitting reduction gear36and the second combined-force reduction gear51rotates faster than the first combined-force reduction gear41.

Like a selection clutch (also referred to as a first selection clutch)45, the selection clutch (also referred to as a second selection clutch)53has engaging protrusions53dformed that laterally protrude from the right side of the selection clutch53. The engaging protrusions53dof the second selection clutch53can be engaged with engaging holes51acircumferentially formed on the second combined-force reduction gear51. As shown inFIG. 11, the second selection clutch53is disposed on the right side, the engaging protrusions53dof the second selection clutch53are inserted into engagement with the engaging holes51aof the second combined-force reduction gear51, transmitting the rotary force of the second combined-force reduction gear51to the combined-force transmission member29through the second selection clutch53. The second selection clutch53disposed on the left side as shown inFIGS. 8 to 10is not engaged with the second combined-force reduction gear51or, as a matter of course, the first combined-force reduction gear41.

With this configuration, if a manual gear change part18is operated to a first speed, the first selection clutch45is set at the left position ofFIGS. 8 and 9so as to be engaged with the human-power transmitting reduction gear36. Thus, as in the setting to the first speed in the foregoing embodiment, a driving sprocket13is rotated at a relatively low speed (first speed) relative to the rotations of pedals8so as to rotate a rear wheel4, thereby keeping traveling.

If the manual gear change part18is operated to a second speed, the first selection clutch45is set at the right position ofFIG. 10so as to be engaged with the first combined-force reduction gear41. Thus, as in the setting to the second speed in the foregoing embodiment, the driving sprocket13is rotated at a relatively high speed (second speed) relative to the rotations of the pedals8so as to rotate the rear wheel4, thereby keeping traveling. If the manual gear change part18is set at the first and second speeds, a second selection clutch43is set at the left position and is not engaged with the second combined-force reduction gear51.

If the manual gear change part18is operated to a third speed, as shown inFIG. 11, the first selection clutch45moves to the intermediate position and is not engaged with the human-power transmitting reduction gear36or the first combined-force reduction gear41. Meanwhile, the second selection clutch53is set at the right position with the engaging protrusions53dthereof inserted into engagement with the engaging holes51aof the second combined-force reduction gear51.

Thus, when the pedals8are rotated forward in this state, a human driving force from the pedal8is transmitted to the human-power transmitting reduction gear36through the crank shaft7a, a human-power transmission member28, an interlocking cylindrical part23, and a one-way clutch (one-way clutch for interrupting an auxiliary driving force)30as in the setting to the second speed. Subsequently, the human driving force is transmitted from the human-power transmitting reduction gear36to the intermediate shaft44through the second intermediate-shaft reduction gear38. Moreover, an auxiliary driving force corresponding to the human driving force is outputted from a motor21and a turning force from the motor21is transmitted to the intermediate shaft44through a first intermediate-shaft reduction gear37and a one-way clutch (one-way clutch for interrupting a human driving force)47. This combines the human driving force and the auxiliary driving force on the intermediate shaft44.

Subsequently, the combined force of the intermediate shaft44is transmitted to the second combined-force reduction gear51through the fourth intermediate-shaft reduction gear52and then is transmitted to the driving sprocket13through the second selection clutch53and the combined-force transmission member29, rotating the driving sprocket13at the third speed higher than the second speed.

With this configuration, the first and second selection clutches45and53are selectively engaged with the human-power transmitting reduction gear36or the first and second combined-force reduction gears41and51, thereby satisfactorily transmitting a combined force to the rear wheel4with a gear change from the first speed to the third speed. Similarly, gears can be changed in multiple steps, for example, at least four steps by adding an intermediate-shaft reduction gear, a combined-force reduction gear, a selection clutch, and so on.

In the present embodiment, the one-way clutch30for interrupting an auxiliary driving force is disposed between the human-power transmission member28having a magneto-striction generation portion31bof a torque sensor31formed and the combined-force transmission member29where the driving sprocket13is attached (in the present embodiment, between the interlocking cylindrical part23and the human-power transmitting reduction gear36). The present invention is not limited to this configuration. The one-way clutch30for interrupting an auxiliary driving force may not be provided. For example, as shown inFIGS. 12 and 13, the human-power transmission member28and the human-power transmitting reduction gear36may be integrally rotated while being engaged at serration parts (or spline parts)28aand36b.

In this case, even if a rider stops pressing the pedals8, so-called delay control keeps driving the motor21for a while. This may allow the crank shaft7aand the pedals8to continuously rotate by themselves. Thus, in order to prevent such a phenomenon, it is preferable to immediately stop or brake the motor21when the rotation detector10quickly detects, according to the rotational state of the combined-force transmission member29, the human-power transmission member28, or the crank shaft7a, that a rider stops pressing the pedals8.

With this configuration, a reversed rotation of the pedal8is smoothly transmitted from the crank shaft7ato the rear wheel4through the combined-force transmission member29, the human-power transmission member28, the driving sprocket13, a chain15, and so on. For example, the hub of the rear wheel may have a coaster brake that operates when the pedals are rotated opposite to a forward rotation. Specifically, in this case, a reversed rotation of the pedal8is transmitted through the chain15and so on to the coaster brake provided on the hub of the rear wheel4. This can satisfactorily operate the coaster brake.

In the present embodiment, a clutch driving part46that drives the selection clutches45and53is movable along a guide rod48laterally extending in parallel with the crank shaft7a. In this state, the clutch driving part46moves the selection clutch45held with the forked end of the clutch driving part46. The present invention is not limited to this configuration. For example, the selection clutch may be moved using a cam mechanism or using a clutch driving part that swings about a support point.

INDUSTRIAL APPLICABILITY

The present invention is applicable to various electric assist bicycles, each being capable of traveling with a combination of a human driving force generated by a pedal force from a pedal and an auxiliary driving force generated by a motor.