Power tool

To provide a hand-held power tool which is equipped with a motor and can be used in a normal driving mode for a tip end tool and also in driving modes other than the normal driving mode. A power tool in which a tip end tool is driven by a motor to thereby perform a predetermined machining process on a workpiece, wherein the motor is a dual rotor motor comprising: an inner rotor; an outer rotor; and a stator including a driving coil mechanism, with the inner rotor and the outer rotor being coaxially disposed.

FIELD OF THE INVENTION

The present invention relates to a power tool that performs a predetermined operation on a workpiece with a tool bit driven by a motor.

BACKGROUND OF THE INVENTION

Japanese laid-open patent publication No. 2007-295773 discloses a hand-held power tool which is capable of controlling output torque of a tool bit driven by a motor. This power tool is constructed to tighten a screw by giving impact in the circumferential direction and rotation to the tool bit in the form of a screw bit.

In the known screw tightening machine, however, by provision of the construction in which rotation and impact are given to the tool bit, it is likely to have a complicated device configuration by any means.

DISCLOSURE OF THE INVENTION

Problems to be Solved by the Invention

Accordingly, it is an object of the present invention to provide a power tool that can realize various kinds of required operations in a simple device configuration.

Means for Solving the Problem

In order to solve the above-described problem, according to a preferred embodiment of the present invention, a power tool is provided which performs a predetermined operation on a workpiece with a tool bit driven by a motor. The “predetermined operation” in the present invention represents an operation of tightening screws, bolts or the like by rotationally driving the tool bit in the form of a screw bit or a socket. It however widely includes not only the tightening operation, but a chipping or drilling operation by linearly driving a hammer bit or by rotationally driving it around its axis, and a cutting operation by rotationally driving a saw blade.

In the preferred embodiment of the power tool of the present invention, it is characterized in that the motor includes an inner rotor, an outer rotor and a stator having a driving coil mechanism and is configured as a dual rotor motor in which the inner rotor is arranged coaxially inside of the outer rotor.

The inner rotor and the outer rotor of the dual rotor motor can be driven and stopped independently from each other. Therefore, it may be constructed to drive the tool bit by using both the inner rotor and the outer rotor, or alternatively, to drive the tool bit by using one of the inner rotor and the outer rotor and drive an actuating member other than the tool bit by using the other rotor.

If it is constructed to drive the tool bit by using both the inner rotor and the outer rotor, for example, in the case of the power tool in the form of a screw tightening machine, it can be constructed to rotationally drive the tool bit in the form of a screw bit by using one of the rotors while giving impact to the screw bit in the circumferential direction by using the other rotor. Further, if it is constructed to drive the tool bit by using one of the inner rotor and the outer rotor and drive an actuating member other than the tool bit by using the other rotor, it can be constructed to drive the actuating member other than the tool bit, for example, in the form of a motor cooling fan. Thus, according to this invention, various kinds of required operations can be realized in a simple device configuration. Further, the dual rotor motor can be arranged coaxially with an output shaft which drives the tool bit. Therefore, for example, compared with a construction in which two motors are arranged in parallel, the machine body is not bulged outward so that the compact power tool can be provided.

According to a further embodiment of the power tool of the present invention, the stator is formed by a single member. In this case, the “driving coil mechanism” may be constructed to include an inner rotor driving coil for driving the inner rotor and an outer rotor driving coil for driving the outer rotor, or it may be constructed to include one driving coil for driving both the inner rotor and the outer rotor.

According to a further embodiment of the power tool of the present invention, the stator includes a plurality of members, or a first stator having an inner rotor driving coil for driving the inner rotor and a second stator having an outer rotor driving coil for driving the outer rotor.

According to a further embodiment of the power tool of the present invention, in the construction in which the stator includes the first stator and the second stator, the power tool has a housing for housing the dual rotor motor, and the inner motor includes the inner rotor and the first stator and the outer motor includes the outer rotor and the second stator. Further, the inner motor and the outer motor are arranged in the housing at positions displaced from each other in the longitudinal direction, and a space is formed between an outer circumferential region of the inner motor and the housing. The “longitudinal direction” in this invention refers to the axial direction of the rotation axis of the inner rotor and the outer rotor.

According to this embodiment, the outer circumferential region of the inner motor can be supported (fixed) from outside by the housing. Therefore, compared with a structure of supporting an end surface (side) of the inner motor in the longitudinal direction, it can be firmly supported with a simpler structure. Specifically, in order to support the outer circumferential region of the inner motor, the outer circumferential region of the first stator is fixed to the housing directly or via a supporting member such as an annular member.

According to a further embodiment of the power tool of the present invention, the first and second stators are partly aligned in contact with each other in a radial direction transverse to the longitudinal direction and connected together in the aligned region.

According to this embodiment, the first and second stators can be connected together in a rational manner. For example, mechanical connection using pins, screws or the like, connection via a resin layer by resin molding, or connection using an adhesive can be used.

According to a further embodiment of the power tool of the present invention, the outer motor is configured as an axial gap motor in which the outer rotor and the second stator are opposed to each other in the longitudinal direction. In such a case, preferably, the first and second stators are partly aligned in the longitudinal direction and connected together in the aligned region. Further, preferably, the outer circumferential region of the second stator of the outer motor is fixedly supported by the housing directly or via a supporting member.

According to this embodiment, the dual rotor motor using a normal radial gap motor and an axial gap motor can be provided.

According to a further embodiment of the power tool of the present invention, the power tool has a speed reducing mechanism. Further, the dual rotor motor drives the tool bit via the speed reducing mechanism, and the speed reducing mechanism has at least first and second speed reduction ratios and switches at least one of the inner and outer rotors between a driven state and a stopped state to thereby switch between the first and second speed reduction ratios. In this case, preferably, the switching between the speed reduction ratios is made according to any one of an electric current value, torque, rotation speed and temperature of the dual rotor motor.

According to a further embodiment of the power tool of the present invention, the output torque to be outputted to the tool bit is changed by the switching between the first and second speed reduction ratios.

According to this embodiment, the output torque of the tool bit can be changed by switching between the first and second speed reduction ratios. Therefore, the dual rotor motor can be used to drive the tool bit at high torque or low torque according to the load on the tool bit, during operation by the tool bit.

According to a further embodiment of the power tool of the present invention, the rotation speed of the tool bit is changed by the switching between the first and second speed reduction ratios.

According to this embodiment, the rotation speed of the tool bit can be changed between high speed and low speed by switching between the first and second speed reduction ratios. Therefore, by using the dual rotor motor, during operation by the tool bit, the tool bit can be driven at high speed in low load conditions, while it can be driven at low speed in high load conditions.

According to a further embodiment of the power tool of the present invention, the output torque of the tool bit is intermittently changed by continuously driving one of the inner rotor and the outer rotor and intermittently driving the other rotor.

According to this embodiment, the output torque of the tool bit can be intermittently changed. Therefore, for example, in the case of the power tool in the form of a screw tightening machine, by provision for intermittently changing the output torque of the tool bit after a screw is seated on the workpiece, the screw tightening machine of an impact type can be realized without need of using a mechanical mechanism such as a rotational impact mechanism for intermittently applying impact to the tool bit in the form of a screw bit in the direction of rotation.

According to a further embodiment of the power tool of the present invention, the speed reducing mechanism is formed by a planetary gear mechanism. Further, the planetary gear mechanism includes a sun gear and an internal gear which are coaxially arranged and a planetary gear which engages with both the sun gear and the internal gear and revolves around the sun gear. The internal gear is connected to the outer rotor and the sun gear is connected to the inner rotor. A difference of relative rotation between the sun gear and the internal gear is controlled by control of rotational driving of the outer rotor and the inner rotor, so that the revolution speed of the planetary gear is changed to switch the speed reduction ratio.

According to this embodiment, the dual rotor motor and the planetary gear mechanism can be connected to each other in a rational arrangement.

According to a further embodiment of the power tool of the present invention, in the construction in which the speed reducing mechanism is formed by the planetary gear mechanism, the inner rotor is constantly driven.

According to this embodiment, when the sun gear of the planetary gear mechanism is constantly driven by the inner rotor, the planetary gear which engages with the sun gear revolves while rotating. In this case, when the outer rotor is stopped, the internal gear is held in the stopped state. When the outer rotor is rotationally driven in the same direction as the inner rotor or in the opposite direction, the internal gear is rotationally driven in the same direction as the sun gear or in the opposite direction, so that the revolution speed of the planetary gear is changed. Thus, according to this embodiment, the speed reduction ratio of the planetary gear mechanism can be changed by switching the outer rotor between the driven state and the stopped state.

According to a further embodiment of the power tool of the present invention, in the construction in which the speed reducing mechanism is formed by the planetary gear mechanism, the outer rotor is constantly driven.

According to this embodiment, when the internal gear of the planetary gear mechanism is constantly driven by the outer rotor, the planetary gear which engages with the internal gear revolves while rotating. In this case, when the inner rotor is stopped, the sun gear is held in the stopped state. When the inner rotor is rotationally driven in the same direction as the outer rotor or in the opposite direction, the sun gear is rotationally driven in the same direction as the internal gear or in the opposite direction, so that the revolution speed of the planetary gear is changed. Thus, according to this embodiment, the speed reduction ratio of the planetary gear mechanism can be changed by switching the inner rotor between the driven state and the stopped state.

According to a further embodiment of the power tool of the present invention, the power tool includes a one-way clutch which is disposed between the outer rotor and the internal gear or between the inner rotor and the sun gear and transmits torque from the outer rotor and internal gear side to the tool bit side, but not in the reverse direction. The one-way clutch locks the internal gear or the sun gear against rotation according to torque on the tool bit and independently of rotation of the outer rotor or the inner rotor.

According to this embodiment, when the outer rotor or the inner rotor is stopped, the internal gear or the sun gear can be locked against rotation by the clutch. Therefore, reverse input of power from the internal gear or the sun gear to the outer rotor or the inner rotor can be interrupted, so that the motor can be protected.

According to a further embodiment of the power tool of the present invention, a fan is provided as the actuating member other than the tool bit. One of the inner rotor and the outer rotor of the dual rotor motor drives the tool bit and the other rotor drives the fan.

According to this embodiment, the fan provided as the actuating member other than the tool bit can be driven on the same axis.

According to a further embodiment of the power tool of the present invention, the outer rotor has an extending region formed on one end of the outer rotor in the longitudinal direction and extending forward of front ends of the stator and the inner rotor in the longitudinal direction. Further, the fan is disposed inside of the extending region of the outer rotor. With such a construction, a rational arrangement can be realized. In this case, the fan can be constructed to be constantly or intermittently driven.

According to a further embodiment of the power tool of the present invention, the fan is provided as a cooling fan for cooling the dual rotor motor. The cooling fan is constructed to be constantly driven, or to be intermittently driven according to at least one of the temperature, rotation speed, torque and electric current value of the dual rotor motor.

According to a further embodiment of the power tool of the present invention, the fan is provided as a dust collecting fan for collecting dust generated during operation and driven upon request for dust collection. The time of “request for dust collection” here typically represents the time when, in the case of the power tool in the form of a drilling or cutting tool, the tool bit is rotationally driven to perform a drilling or cutting operation.

EFFECT OF THE INVENTION

According to the present invention, a power tool is provided which can realize various kinds of required operations in a simple device configuration. Other objects, features and advantages of the present invention will be readily understood after reading the following detailed description together with the accompanying drawings and the claims.

REPRESENTATIVE EMBODIMENT FOR PERFORMING THE INVENTION

Each of the additional features and method steps disclosed above and below may be utilized separately or in conjunction with other features and method steps to manufacture and use improved power tools and methods for using them and devices utilized therein. Representative examples of the present invention, which examples utilized many of these additional features and method steps in conjunction, is now described in detail with reference to the drawings. This detailed description is merely intended to teach a person skilled in the art further details for practicing preferred aspects of the present teachings and is not intended to limit the scope of the invention. Only the claims define the scope of the claimed invention. Therefore, combinations of features and steps disclosed within the following detailed description may not be necessary to practice the invention in the broadest sense, and are instead taught merely to particularly describe some representative examples of the invention, which detailed description will now be given with reference to the accompanying drawings.

(First Embodiment of the Invention)

A first embodiment of the present invention is now described with reference toFIGS. 1 to 4. A battery-powered screwdriver is described as a representative embodiment of a hand-held power tool according to the present invention.FIG. 1shows a screwdriver101according to this embodiment. As shown inFIG. 1, the screwdriver101according to this embodiment mainly includes a body103which forms an outer shell of the screwdriver101, a screw bit119detachably coupled to a front end of a spindle115via a bit holder117in a front end region (left end region as viewed inFIG. 1) of the body103, and a handgrip (handle)109connected integrally to the body103. The body103and the screw bit119are features that correspond to the “tool body” and the “tool bit”, respectively, according to the present invention. Further, in this embodiment, for the sake of convenience of explanation, the side of the screw bit119is taken as the front and the opposite side as the rear.

The body103mainly includes a motor housing105that houses a driving motor111, and a gear housing107that houses a speed reducing mechanism in the form of a planetary gear mechanism113and an output shaft in the form of the spindle115in front (on the left as viewed inFIGS. 1 and 2) of the driving motor111. The driving motor111is a feature that corresponds to the “motor” and the “dual rotor motor” according to the present invention. The motor housing105has right and left halves connected to each other and covers the entire region of the gear housing107other than its front end region for supporting the spindle115. The handgrip109extends in a downward direction transverse to the longitudinal direction of the body103(the axial direction of the screw bit119), and a battery pack110is removably attached to the extending end of the handgrip109. The battery pack110contains a battery by which the driving motor111is powered.

FIG. 2shows a construction of an essential part of the screwdriver. As shown in the drawing, the driving motor111includes an inner rotor121(first rotor), an outer rotor123(second rotor), and a stator125formed of a doughnut-shaped single member. An inner rotor driving coil (not shown) for driving the inner rotor121and an outer rotor driving coil (not shown) for driving the outer rotor123are wound on the stator125. The driving motor111is a dual rotor motor having the inner rotor121and the outer rotor123arranged coaxially inside and outside of the stator125, respectively. The inner rotor driving coil for driving the inner rotor121and the outer rotor driving coil for driving the outer rotor123form the “driving coil mechanism” according to this invention.

The stator125is generally doughnut-shaped and fixedly mounted at its rear end to the motor housing of the body103. The inner rotor121inside of the stator125is rotatably supported at its front end with respect to the stator125via a bearing127and also rotatably supported at its rear end with respect to the motor housing105via a bearing128. The outer rotor123is generally cylindrically shaped and rotatably supported at its front and rear ends of its outer circumferential surface with respect to the motor housing105via bearings129. The inner rotor121and the outer rotor123are driven and stopped independently from each other.

The planetary gear mechanism113is disposed in front of the driving motor111. The rotation output of the driving motor111is reduced in speed by the planetary gear mechanism113and transmitted to the spindle115and then to the screw bit119which is held by the spindle115via the bit holder117. The planetary gear mechanism113is a feature that corresponds to the “speed reducing mechanism” according to the present invention.

The planetary gear mechanism113includes a first sun gear131, a first internal gear (ring gear)133, a plurality of first planetary gears135, a first carrier137, a second sun gear139, a second internal gear141, a plurality of second planetary gears143and a second carrier145. The planetary gear mechanism113reduces the speed of the rotation output of an inner rotor shaft121aand transmits the rotation output to the spindle115.

The first sun gear131is connected to the inner rotor shaft121aof the inner rotor121and rotates together. The first internal gear (ring gear)133is a ring-like member and has an outer surface rotatably supported with respect to the gear housing107and an inner surface having teeth. The first internal gear133is rotationally driven by the outer rotor123. The first planetary gears135are engaged with the first sun gear131and the first internal gear133and revolve around the rotation axis of the first sun gear131. The first carrier137rotatably supports the first planetary gears135and rotates around the same axis as the first sun gear131. The second sun gear139is integrally formed on one (front) end of an outer circumferential surface of the first carrier137in the axial direction. The second internal gear141is fixed to the gear housing107and held in the stopped state at all times. The second planetary gears143are engaged with the second sun gear139and the second internal gear141and revolve around the rotation axis of the second sun gear139. The second carrier145rotatably supports the second planetary gears143and is connected to the spindle115via an overload clutch147.

The overload clutch147is a known machine element which is provided to interrupt transmission of torque from the second carrier145to the spindle115when an excessive load is applied to the spindle115. Therefore, its detailed description is omitted. Further, the planetary gear mechanism113of this embodiment is constructed to have two carriers, or the first carrier137for supporting the first planetary gears135and the second carrier145for supporting the second planetary gears143, which are connected in series in the axial direction, but it is not necessary to have two carriers.

The outer rotor123is connected to the first internal gear133of the planetary gear mechanism113via a bi-directional one-way clutch151. The bi-directional one-way clutch151is a feature that corresponds to the “clutch” according to the present invention. As shown inFIGS. 3 and 4, the bi-directional one-way clutch151mainly includes a ring-like fixed outer ring158which forms an outer shell of the bi-directional one-way clutch151and is integrally formed with the gear housing107, a power transmitting part153which is integrally formed with an input shaft in the form of the outer rotor123, a power receiving member157which is connected to the first internal gear133, and a columnar lock pin159which is disposed between the power transmitting part153and the power receiving member157. The lock pin159locks the first internal gear133against rotation when torque is inputted from the first internal gear133on the output side to the outer rotor123on the input side.

The power transmitting part153consists of a plurality of members having a circular arc section and extending a predetermined length from the front end region of the outer rotor123in the axial direction, at predetermined intervals in the circumferential direction (four at 90-degree intervals in this embodiment). The power transmitting parts153are disposed for relative rotation inside of the fixed outer ring158. The power receiving member157has a disc-like shape having a circular hole through which the first sun gear131can be loosely inserted. The power receiving member157is disposed for relative rotation inside of the power transmitting parts153. The power receiving member157has two power receiving parts155formed on its outer surface with a 180-degree phase difference and protruding radially outward. The power receiving parts155are disposed with a predetermined clearance in the circumferential direction in two of the spaces which are defined between adjacent ones of the power transmitting parts153and have a 180-degree phase difference. The lock pins159are disposed in the other two of the spaces defined between adjacent ones of the power transmitting parts153and having a 180-degree phase difference.

When the outer rotor123is rotationally driven clockwise, one of the power transmitting parts153disposed on the opposite sides of the power receiving part155of the power receiving member157gets into contact with the power receiving part155in the circumferential direction and transmits torque to the first internal gear133in the clockwise direction. When the outer rotor123is rotationally driven counterclockwise, the other power transmitting part153disposed on the opposite side of the power receiving part155gets into contact with the power receiving part155in the circumferential direction and transmits torque to the first internal gear133in the counterclockwise direction.FIG. 3shows the state in which the outer rotor123is rotationally driven counterclockwise.

The lock pins159are disposed between the outer surface of the power receiving member157and the inner surface of the fixed outer ring158in the spaces defined between the adjacent power transmitting parts153. A planar region157ais tangentially formed on the outer surface of the power receiving member157in the spaces in which the lock pins are disposed. Therefore, as shown inFIG. 3, when the outer rotor123is rotationally driven, each of the lock pins159is about to be wedged into a wedge-shaped space between the outer surface of the power receiving member157and the inner surface of the fixed outer ring158by the difference of relative rotation between the power receiving member157and the fixed outer ring158. At this time, however, the lock pin159is pushed by a front end surface of the power transmitting part153in the rotation direction and held on the planar region157a. Therefore, the lock pin159is not wedged in and the torque of the outer rotor123is transmitted to the first internal gear133via the power receiving member157.

When torque is inputted from the output side to the input side, or more specifically, for example, when load is applied to the first internal gear133(the spindle115) side and the power receiving member157is about to rotate with respect the power transmitting part153in the state shown inFIG. 4, the power receiving member157is locked in contact with the inner surface of the fixed outer ring158via the lock pins159. Specifically, the lock pins159are wedged into the wedge-shaped spaces between the outer surface of the power receiving member157and the inner surface of the fixed outer ring158, so that the power receiving member157is locked to the fixed outer ring158.

As described above, the bi-directional one-way clutch151is provided as a machine element which can transmit torque of the outer rotor123on the input (driving) side to the first internal gear133(the spindle115) on the output (driven) side both in the clockwise and counterclockwise directions. Moreover, when torque is about to be inputted reversely from the output side to the input side by load applied to the output side, the bi-directional one-way clutch151locks the first internal gear133and interrupts transmission of torque from the output side to the input side both in the clockwise and counterclockwise directions.

In this embodiment, when the first internal gear133is locked and the inner rotor121of the driving motor111is electrically driven, the spindle115is caused to rotate at a certain reduction ratio predetermined in the planetary gear mechanism113. In this state, when the outer rotor123is rotated in the same direction as the inner rotor121, the first internal gear133serving as a reaction force receiving member rotates in the same direction as the first sun gear131. As a result, the number of revolutions of the first planetary gears135around the first sun gear131increases by the number of rotations of the first internal gear133, so that the rotation speed of the spindle115increases. On the other hand, when the outer rotor123is rotated in the opposite direction, the number of revolutions of the first planetary gears135decreases by the number of rotations of the first internal gear133, so that the rotation speed of the spindle115decreases.

In this manner, according to this embodiment, the outer rotor123can be switched between the stopped state and the driven state in which it is driven in the same direction as the inner rotor121or in the opposite direction, while the inner rotor121is constantly and continuously driven. By this switching, the revolution speed of the first planetary gears135(the rotation speed of the first carrier137) can be changed so that the speed reduction ratio of the planetary gear mechanism113can be changed. Specifically, the output torque and the rotation speed to be outputted to the spindle115can be changed by changing the speed reduction ratio of the planetary gear mechanism113. Further, the speed reduction ratio is changed according to load on the spindle115such as the driving current, torque, rotation speed and temperature of the driving motor111. The speed reduction ratios set by switching the outer rotor123to the stopped state and the driven state while the inner rotor121is constantly driven are features that correspond to the “first and second speed reduction ratios”, respectively, according to this embodiment.

In order to tighten a fastener such as a screw and a bolt (hereinafter referred to as a screw or the like) by using the screwdriver101, the screw or the like is pressed against a workpiece via the screw bit119, and in this state, a trigger109aon the handgrip109is depressed to drive the driving motor111. As a result, the spindle115is rotationally driven via the planetary gear mechanism113, and the screw bit119rotates together with the spindle115and is allowed to perform the operation of tightening a screw or the like.

In this case, in this embodiment, the first sun gear131is constantly driven by the inner rotor121of the driving motor111, and the first internal gear133can be driven and stopped by the outer rotor123.

Specifically, the outer rotor123is intermittently driven, or repeatedly alternates between driving and stopping while the screw bit119is driven by constantly driving the inner rotor121. In this manner, the screw bit119which is being driven at an output torque outputted by the inner rotor121intermittently gains the output torque outputted by the outer rotor123. Thus, torque for driving the screw bit119can be intermittently changed. In the following description, intermittent torque change is also referred to as a torque ripple.

Thus, according to this embodiment, by intermittently driving the outer rotor123, the operation of temporarily increasing the output torque to be outputted to the screw bit119and then immediately returning it to its initial state can be repeated. As a result, a smaller reaction force is required to hold the screwdriver101. Therefore, the screwdriver101can be provided which can perform a screw tightening operation at a higher tightening torque than a usual tightening torque and is easy for a user to hold.

It may be constructed such that torque ripple is caused by intermittent driving of the outer rotor123all the way through the screw tightening operation of the screw bit119which is constantly driven by the inner rotor121, or such that it is caused somewhere in the screw tightening operation. In order to cause torque ripple somewhere, suitably, for example, torque ripple may be caused by intermittently driving the outer rotor123when load (tightening torque) increases upon seating of the screw on the workpiece during screw tightening operation of the screw bit119driven by the inner rotor121.

Therefore, according to this embodiment, the impact type screwdriver101equivalent to one having a mechanical rotary impact mechanism which intermittently applies impact force to the screw bit119in the direction of rotation can be obtained without such a rotary impact mechanism. Further, in the case of the construction in which the outer rotor123is intermittently driven somewhere during driving of the screw bit119by the inner rotor121, for example, at least one of the driving current, torque, rotation speed and temperature of the constantly driven inner rotor121may be detected by a detector, and a motor control device (controller) which is not shown may be used to control such that the outer rotor123starts intermittent driving when the value detected by the detector reaches a predetermined value.

The first internal gear133receives a reaction force when the screw bit119is rotationally driven by the inner rotor121. Therefore, the outer rotor123needs to generate higher torque than the inner rotor121in order to cause torque ripple by driving of the outer rotor123. During the time when torque ripple is not caused, or when the screw bit119is driven only by driving of the inner rotor121, the first internal gear133needs to be held in the locked state. If the first internal gear133is held in the locked state only by torque of the outer rotor123, the outer rotor123is used in the locked state, which may cause motor burnout. According to this embodiment, however, the bi-directional one-way clutch151is provided between the outer rotor123and the first internal gear133of the planetary gear mechanism113and interrupts reverse input of power from the first internal gear133on the driven side to the outer rotor123on the input side so that the first internal gear133can be held in the locked state. Thus, the outer rotor123can be protected from burnout.

Further, in this embodiment, the rotation axis of the dual rotor motor which forms the driving motor111is arranged coaxially with the spindle115which drives the screw bit119. Therefore, for example, compared with a construction in which two motors are arranged in parallel, the machine body is not bulged outward so that the compact screwdriver101can be provided.

Further, in this embodiment, a cooling fan161for cooling the motor is provided on the inner rotor121which is constantly driven. The cooling fan161is provided on an axial end (rear end) of the inner rotor121facing away from the first sun gear131. The cooling fan161serves to cool the driving motor111by taking outside air into the space of the motor housing105through an inlet (not shown) formed in the rear end of the motor housing105, leading it forward in the longitudinal direction and then discharging it to the outside through an outlet (not shown) formed in the front of the housing.

(Second Embodiment of the Invention)

A second embodiment of the present invention is now described with reference toFIGS. 5 to 8. In this embodiment, the first internal gear133is constantly driven by the outer rotor123, and the first sun gear131can be driven and stopped by the inner rotor121. To this end, the outer rotor123is directly connected to the first internal gear133, and the bi-directional one-way clutch151is disposed between the inner rotor shaft121aof the inner rotor121and the first sun gear131. In the other points, this embodiment has the same construction as the above-described first embodiment. Therefore, components in this embodiment which are substantially identical to those in the first embodiment are given like numerals as in the first embodiment.

The bi-directional one-way clutch151has basically the same construction and function as that in the first embodiment. Due to arrangement of the bi-directional one-way clutch151between the inner rotor shaft121aand the first sun gear131, however, the fixed outer ring158which forms the outer shell of the bi-directional one-way clutch151is connected to the front surface of the stator125of the driving motor111and has a generally cup-like shape having a circular central opening through which the first sun gear131is loosely inserted. Further, four power transmitting parts153are disposed at predetermined intervals in the circumferential direction and integrally formed with a disc-like power transmitting member152. The power transmitting member152is connected to the inner rotor shaft121aand rotates together with the inner rotor shaft121a. The power receiving member157having the power receiving parts155is connected to the first sun gear131and rotates together with the first sun gear131. In the other points, the bi-directional one-way clutch151has the same construction as that in the first embodiment.

Therefore, when the inner rotor121is driven, as shown inFIG. 7, the lock pin159is pushed by the front end surface of the power transmitting part153in the rotation direction, so that each of the lock pins159is not wedged into a wedge-shaped space between the outer surface of the power receiving member157and the inner surface of the fixed outer ring158. Therefore, the power transmitting part153comes into contact with the power receiving part155in the circumferential direction and transmits torque to the first sun gear131. When torque is inputted from the output side to the input side, or more specifically when load is applied to the first sun gear131(the spindle115) side and the power receiving member157is about to rotate with respect the power transmitting member152in the state shown inFIG. 8, the lock pins159are wedged into the wedge-shaped spaces between the outer surface of the power receiving member157and the inner surface of the fixed outer ring158, so that the power receiving member157is locked to the fixed outer ring158.

Specifically, when the inner rotor121on the input (driving) side is driven, the bi-directional one-way clutch151can transmit torque of the inner rotor121to the first sun gear131(the spindle115) on the output (driven) side both in the clockwise and counterclockwise directions. Moreover, when torque is about to be inputted reversely from the output side to the input side by load applied to the output side, the bi-directional one-way clutch151locks the first sun gear131and interrupts transmission of torque from the output side to the input side both in the clockwise and counterclockwise directions.

In this embodiment, the first internal gear133is constantly driven by the outer rotor123of the driving motor111, and the first sun gear131can be driven and stopped by the inner rotor121. Therefore, while the spindle115(the screw bit119) is driven by driving the outer rotor123, the inner rotor123is intermittently driven, or repeatedly alternates between driving and stopping. In this manner, the screw bit119which is being driven at an output torque outputted by the outer rotor123intermittently gains the output torque outputted by the inner rotor121. Thus, according to this embodiment, torque for driving the screw bit119can be intermittently changed.

Thus, according to this embodiment, by intermittently driving the inner rotor121, the operation of temporarily increasing the output torque to be outputted to the screw bit119and then immediately returning it to its initial state can be repeated. Therefore, for example, when load (tightening torque) increases upon seating of the screw on the workpiece during screw tightening operation, torque ripple can be caused by intermittently driving the inner rotor121, and the screw tightening operation can be performed at a higher tightening torque than a normal tightening torque.

Further, in this embodiment, the first sun gear131receives a reaction force when the screw bit119is rotationally driven by the outer rotor121. Therefore, the inner rotor121needs to generate higher torque than the outer rotor123in order to cause torque ripple by intermittent driving of the inner rotor123. During the time when torque ripple is not caused, the first sun gear131needs to be held in the locked state by stopping driving the inner rotor121. If the first sun gear131is held in the locked state only by torque of the inner rotor121, motor burnout may be caused. According to this embodiment, however, the bi-directional one-way clutch151provided between the inner rotor121and the first sun gear131can interrupt reverse input of power from the driven-side first sun gear131to the input-side inner rotor121and hold the first internal gear133in the locked state. Thus, the outer rotor123can be protected from burnout.

Further, in this embodiment, a cooling fan163for cooling the motor is provided on the outer rotor123which is constantly driven. The cooling fan163is provided on the inner circumferential surface of an axial end (rear end) of the outer rotor123on the opposite side from the first internal gear133. The cooling fan163serves to cool the driving motor111by taking outside air into the space of the motor housing105through an inlet formed in the rear end of the motor housing105and leading it forward in the longitudinal direction. The air taken into the motor housing space cools the driving motor111by flowing into the motor through gaps between the stator125and the outer rotor123and between the stator125and the inner rotor121. Thereafter, the air flows out to the outside of the motor through a radially extending communication hole123aformed through a front end region of the outer rotor123. The air then further passes between the motor housing105and the gear housing107and is discharged to the outside through an outlet.

According to this embodiment, not only the above-described effects but the same effects as the first embodiment can be obtained, which are not described in order to avoid redundant description.

(Third Embodiment of the Invention)

A third embodiment of the present invention is now described with reference toFIGS. 1 to 4. In this embodiment, the screw bit119is constantly driven by using one of the rotors, and in this state, the speed reduction ratio of the planetary gear mechanism113can be changed according to the load (tightening torque) on the screw bit119(the spindle115) by using the other rotor, so that the rotation speed (screw tightening speed) of the screw bit119can be automatically changed.

The entire construction of the screwdriver101is the same as the above-described first embodiment and therefore it is not described. In this embodiment, it is constructed such that the inner rotor121and the outer rotor123are simultaneously driven when the trigger109ais depressed.

For example, when the load is low until the screw is seated on the workpiece (the head of the screw comes into contact with the workpiece) after start of the screw tightening operation, the first internal gear133receives a small reaction to the rotation driving force. In this state, the first sun gear131is rotationally driven by the inner rotor121, and the first internal gear133is rotationally driven in the direction of rotation of the first sun gear131. Therefore, the screw bit119is rotated together with the spindle115at high speed at the speed reduction ratio at which the first sun gear131and the first internal gear133rotate together.

When the screw is seated on the workpiece and the load is increased, the first internal gear133receives an increased reaction to the rotation driving force. At this time, since the driving force of the outer rotor123is low, the torque of the outer rotor123succumbs to this reaction force, so that the first internal gear133is about to be rotated in the reverse direction. As a result, the bi-directional one-way clutch151is actuated and locks the first internal gear133to the fixed outer ring158. Therefore, the screw bit119is rotated together with the spindle115at low speed at the speed reduction ratio at which only the first sun gear131rotates. The low-speed rotation of the spindle115is detected, for example, by electric current values. Specifically, a current detector is used to detect that the driving current of the outer rotor123has reached a predetermined value. The motor control device (controller) receives this detected signal and stops energization for driving the outer rotor123, so that the outer rotor123can be protected from burnout. The speed reduction ratio at which the first sun gear131and the first internal gear133rotate together and the speed reduction ratio at which only the first sun gear131rotates are features that correspond to the “first and second speed reduction ratios”, respectively, according to this invention.

According to this embodiment, the spindle115can be rotated at high speed in low load conditions in which the tightening torque is low, while it can be rotated at low speed in high load conditions in which the tightening torque is increased. With this construction, a screw tightening operation can be performed more rapidly with higher accuracy. Further, according to this embodiment, it can be provided such that the output torque of the outer rotor123is lower than the output torque of the inner rotor121, so that the outer rotor123can be reduced in size.

(Fourth Embodiment of the Invention)

A fourth embodiment of the present invention is now described with reference toFIGS. 9 and 10. In this embodiment, in the battery-powered screwdriver101, the first sun gear131of the planetary gear mechanism113is driven by the inner rotor121to rotationally drive the spindle115(the screw bit119) via the planetary gear mechanism113, while a cooling fan165is driven by the outer rotor123. In the other points, this embodiment has generally the same construction as the first embodiment except that the bi-directional one-way clutch151is not provided and the first and second internal gears133,141are formed in one piece and fixed to the gear housing107side in the planetary gear mechanism113. Therefore, components in this embodiment which are substantially identical to those in the first embodiment are given like numerals as in the first embodiment, and they are not described.

A cylindrical fan housing part124is formed on one (front) end of the outer rotor123in the longitudinal direction and extends forward of the front ends of the stator125and the inner rotor121(toward the planetary gear mechanism113). The cooling fan165for cooling the motor is housed and fixed within the fan housing part124. The fan housing part124is a feature that corresponds to the “extending region”, and the cooling fan165is a feature that corresponds to the “actuating member other than the tool bit” and the “fan” according to this invention.

In this embodiment, the electric current value of the driving motor111is monitored. When the amount of heat generation of the driving motor111is small, for example, under no load, the cooling fan165is stopped, and when the amount of heat generation of the driving motor111is large, for example, during operation, the outer rotor123is driven to drive the cooling fan165.

According to this embodiment, independently of driving of the spindle115by the inner rotor121, the cooling fan165can be driven by the outer rotor123. Therefore, regardless of the operational status of the spindle115(the screw bit119), the cooling fan165can be constantly driven at the maximum speed. Therefore, the effect of cooling the driving motor111can be improved, so that the driving motor111can be protected from burnout.

Further, the inner rotor121is exclusively used for driving the spindle115and not used for driving the cooling fan165. Accordingly, the output of the inner rotor121is improved. Further, when the amount of heat generation of the driving motor111is small, the cooling fan165can be stopped, so that generation of noise can be lessened.

Further, according to this embodiment, with the construction in which the motor is arranged coaxially with the output shaft or the spindle115, the inner rotor121, the stator125and the outer rotor123can be simultaneously cooled by the one cooling fan165, and the relatively large cooling fan can be mounted without increasing the size of the machine body. Thus, the cooling effect can be easily obtained.

(Fifth Embodiment of the Invention)

A fifth embodiment of the present invention is now described with reference toFIG. 11. This embodiment is a modification to the fourth embodiment and different from the fourth embodiment in that, in addition to the motor cooling fan165mounted to the outer rotor123, a cooling fan167for cooling the motor is mounted to the inner rotor121. In the other points, this embodiment has the same construction as the above-described fourth embodiment. The cooling fan167to be driven by the inner rotor121is provided rearward of the rear end surface of the stator125on the rear end of the inner rotor121. Each of the cooling fans165,167is a feature that corresponds to the “actuating member other than the tool bit” and the “fan” according to this invention.

Therefore, according to the fifth embodiment, the motor is cooled by the cooling fan167even during normal operation in which the spindle115is rotationally driven by driving the inner rotor121. Thus, the operating time of the outer rotor123can be shortened.

Further, the electric current value of the driving motor111is monitored. Under high load or other similar conditions in which the motor may easily burn out, the cooling fan165can be driven by the outer rotor123so that the cooling capacity can be improved. Therefore, this embodiment can be suitably applied to a tightening tool which is used under relatively high-load conditions. Further, the cooling fan165which is driven by the outer rotor123is used only under high-load conditions, so that the amount of screw tightening operation per charge can be easily ensured.

Further, like in the fourth embodiment, with the construction in which the motor is arranged coaxially with the output shaft or the spindle115, the relatively large cooling fan can be mounted without increasing the size of the machine body. Thus, the cooling effect can be easily obtained.

In the first to fifth embodiments in which the stator125is formed by one member, the driving coil mechanism is described as having the inner rotor driving coil for driving the inner rotor121and an outer rotor driving coil for driving the outer rotor123. In place of this construction, however, it may have a construction in which two kinds of electric current are passed through a common driving coil such that the inner rotor121and the outer rotor123are individually driven, or specifically, such that one driving coil is used to drive the inner rotor121and the outer rotor123.

(Sixth Embodiment of the Invention)

A sixth embodiment of the present invention is now described with reference toFIGS. 12 to 22. In this embodiment, the stator125of the driving motor111in the first embodiment is formed by a stator for an outer rotor and a stator for an inner rotor. In the other points, this embodiment has generally the same construction as the above-described first embodiment. Therefore, this embodiment is described with a focus on the driving motor111which is different from that of the first embodiment. The entire construction of the screwdriver101other than the driving motor111, and the planetary gear mechanism113and the bi-directional one-way clutch151which serve as a speed reducing mechanism for transmitting the rotation output of the driving motor111to the spindle115are given like numerals as in the first embodiment, and they are not described or briefly described.

FIG. 13shows an essential part of the screwdriver101. As shown, the driving motor111has an inner rotor121(first rotor), an outer rotor123(second rotor), a stator for the inner rotor (hereinafter referred to as an inner stator)125A on which an inner-rotor driving coil125afor driving the inner rotor121is wound, and a stator for the outer rotor (hereinafter referred to as an outer stator)125B on which an outer-rotor driving coil125bfor driving the outer rotor123is wound. The driving motor111is configured as a dual rotor motor in which the inner rotor121and the outer rotor123are arranged coaxially inside of the inner stator125A and outside of the outer stator125B, respectively. The inner stator125A and the outer stator125B are features that correspond to the “first stator” and the “second stator”, respectively, according to this invention. Further, the inner-rotor driving coil125aand the outer-rotor driving coil125bform the “driving coil mechanism”.

As shown inFIGS. 16 to 19, the inner stator125A and the outer stator125B are generally doughnut-shaped. The inner stator125A includes an annular yoke125A1, a plurality of teeth125A2and a plurality of slots. The teeth125A2extend radially inward from the inner circumferential surface of the yoke125A1and spaced apart from each other, and an inner-rotor driving coil (which is not shown inFIGS. 16 to 19) is wound around the teeth125A2. The outer stator125B has a ring-like stator body125B1, a plurality of teeth125B2and a plurality of slots. The teeth125B2extend radially outward from the outer circumferential surface of the stator body125B1and spaced apart from each other, and an outer-rotor driving coil (which is not shown inFIGS. 16 to 19) is wound around the teeth125B2.

In this embodiment, as shown inFIG. 21, the inner rotor121having four magnets121bfixed on its outer circumferential surface and the inner stator125A having six slots form a four-pole six-slot inner motor. Further, as shown inFIG. 22, the outer rotor123having eight magnets123bfixed on the inner circumferential surface of the outer rotor123and the outer stator125B having eight slots form an eight-pole six-slot outer motor. As shown inFIGS. 13 and 20, the inner motor and the outer motor are arranged at positions displaced from each other in the longitudinal direction within the motor housing105, or more specifically, such that the outer motor is located forward of the inner motor.

The yoke125A1of the inner stator125A and the yoke125B1of the outer stator125B have generally the same inner and outer diameters, and a rear surface of the yoke125B1of the outer stator125B and a front surface of the yoke125A1of the inner stator125A are aligned and connected together (seeFIGS. 17 and 20). Specifically, the yokes125A1,125B1of the inner and outer stators125A,125B are configured to be aligned in contact with each other and connected together by a connecting member in the form of a plurality of pins125c(seeFIG. 20) arranged at predetermined intervals in the circumferential direction. Other connecting methods may be provided to connect the inner and outer stators125A,125B in place of the above-described method using the pins125c. For example, mechanical connection using a plurality of screws or the like, connection via a resin layer by resin molding, or connection using an adhesive can be used.

As shown inFIGS. 13 and 20, in the motor housing105in which the inner motor and the outer motor are set, the inner and outer stators125A,125B are arranged at positions displaced from each other in the longitudinal direction and connected together as described above, so that an annular space is created between the outer circumferential region of the yoke125A1of the inner stator125A and the inner wall surface of the motor housing105. In this embodiment, this space is utilized to provide a supporting member126via which the motor housing105can support the outer circumferential region of the yoke125A1from outside. The supporting member126is provided, for example, as an annular member formed separately from the motor housing105, or as an annular member integrally extending inward from the inner wall of the motor housing105. The outer and inner peripheries of the supporting member126are fixed to the motor housing105and the yoke125A1of the inner stator125A, respectively.

The inner rotor121is disposed inside of the inner stator125A. The inner rotor121is rotatably supported at the front via a bearing127with respect to a bearing housing127A which is disposed inside of the outer stator125B, and it is rotatably supported at the rear via a bearing128with respect to the motor housing105. The outer rotor123is generally cylindrical and disposed outside of the outer stator125B. The outer rotor123is rotatably supported on its outer periphery via front and rear bearings128with respect to the motor housing105. The inner rotor121and the outer rotor123are independently and individually driven and stopped. Further, predetermined air gaps are provided between the inner rotor121and the inner stator125A and between the outer rotor123and the outer stator125B.

As shown inFIG. 13, the planetary gear mechanism113is disposed in front of the driving motor111having the above-described construction. The rotation output of the driving motor111is reduced in speed by the planetary gear mechanism113and transmitted to the spindle115and then to the screw bit119which is held by the spindle115via the bit holder117. The planetary gear mechanism113is a feature that corresponds to the “speed reducing mechanism” according to the present invention. Further, the planetary gear mechanism113and the overload clutch147disposed between the planetary gear mechanism113and the spindle115have the same construction and effect as the above-described first embodiment. Therefore, their description is omitted.

The outer rotor123is connected to the first internal gear133of the planetary gear mechanism113via the bi-directional one-way clutch151. The bi-directional one-way clutch151is a feature that corresponds to the “clutch” according to this invention. As shown inFIGS. 14 and 15, the bi-directional one-way clutch151is provided as a machine element which can transmit torque of the outer rotor123on the input side (driving side) to the first internal gear133(the spindle115) on the output side (driven side) both in the clockwise and counterclockwise directions. Moreover, when torque is about to be inputted reversely from the output side to the input side by load applied to the output side, the bi-directional one-way clutch151is locked to interrupt transmission of torque from the output side to the input side both in the clockwise and counterclockwise directions. The bi-directional one-way clutch151has the same construction and effect as the above-described first embodiment. Therefore, their description is omitted.

In this embodiment, when the first internal gear133is locked and the inner rotor121of the driving motor111is electrically driven, the spindle115is caused to rotate at a certain reduction ratio predetermined in the planetary gear mechanism113. In this state, when the outer rotor123is rotated in the same direction as the inner rotor121, the first internal gear133serving as a reaction force receiving member rotates in the same direction as the first sun gear131. As a result, the number of revolutions of the first planetary gears135around the first sun gear131increases by the number of rotations of the first internal gear133, so that the rotation speed of the spindle115increases. On the other hand, when the outer rotor123is rotated in the opposite direction, the number of revolutions of the first planetary gears135decreases by the number of rotations of the first internal gear133, so that the rotation speed of the spindle115decreases.

In this manner, according to this embodiment, the outer rotor123can be switched between the stopped state and the driven state in which it is driven in the same direction as the inner rotor121or in the opposite direction, while the inner rotor121is constantly and continuously driven. By this switching, the revolution speed of the first planetary gears135(the rotation speed of the first carrier137) can be changed so that the speed reduction ratio of the planetary gear mechanism113can be changed. Specifically, the output torque and the rotation speed to be outputted to the spindle115can be changed by changing the speed reduction ratio of the planetary gear mechanism113. Further, the speed reduction ratio is changed according to load on the spindle115such as the driving current, torque, rotation speed and temperature of the driving motor111. The speed reduction ratios set by switching the outer rotor123to the stopped state and the driven state while the inner rotor121is constantly driven are features that correspond to the “first and second speed reduction ratios”, respectively, according to this embodiment.

In this embodiment, the inner rotor121and the inner stator125A form the inner motor and the outer rotor123and the outer stator125B form the outer motor. The inner motor and the outer motor are arranged at positions displaced from each other in the longitudinal direction within the housing105. Therefore, a space is created between the outer circumferential region of the inner motor (or the inner stator125A) and the inner wall surface of the motor housing105. This space is utilized to provide a supporting member126via which the motor housing105can support (hold) the outer circumferential region of the inner stator125A of the inner motor. Therefore, for example, compared with a structure of holding an end surface (side) of the stator in the longitudinal direction, the stator can be firmly supported with a simpler structure.

Further, in this embodiment, the yokes125A1,125B1of the inner and outer stators125A,125B are aligned in contact with each other in the longitudinal direction and connected together by the pins125cin the aligned region. With this construction, the inner and outer stators125A,125B can be connected together in a rational manner.

According to this embodiment, not only the above-described effects but the same effects as the above-described first embodiment can be obtained, which are not described in order to avoid redundant description.

Next, a modification to the driving motor111of the sixth embodiment is described with reference toFIG. 23. The driving motor111of this modification has an inner rotor121(first rotor), an outer rotor123(second rotor), a stator for the inner rotor (hereinafter referred to as an inner stator)125A on which an inner-rotor driving coil125afor driving the inner rotor121is wound, and a stator for the outer rotor (hereinafter referred to as an outer stator)125B on which an outer-rotor driving coil125bfor driving the outer rotor123is wound. The inner rotor121is disposed inside of the inner stator125A, and the outer rotor123is disposed in front of the outer stator125B to face each other. The driving motor111is configured as a dual rotor motor in which the inner rotor121and the outer rotor123are arranged coaxially.

Specifically, in the dual rotor motor of this modification, the inner motor having the inner rotor121and the inner stator125A is configured as a radial gap motor in which the inner rotor121and the inner stator125A are opposed to each other in the radial direction, while the outer motor having the outer rotor123and the outer stator125B is configured as an axial gap motor in which the outer rotor123and the outer stator125B are opposed to each other in the longitudinal direction. In this point, this modification is different from the above-described sixth embodiment.

As shown inFIG. 23, the inner motor having the inner rotor121and the inner stator125A and the outer motor are arranged at positions displaced from each other in the longitudinal direction, or more specifically, such that the outer motor is located forward of the inner motor. An outer circumferential surface of the front end of the yoke125A1of the inner stator125A in the inner motor and an inner circumferential surface of the yoke125B1of the outer stator125B in the outer motor are configured to be aligned in contact with each other and connected together in the aligned region, for example, via a resin layer by resin molding, or by using an adhesive.

In this modification, the outer motor is configured as an axial gap motor in which the outer rotor123and the outer stator125B are opposed to each other in the longitudinal direction, so that a space is created between the outer circumferential surface of the outer stator125B and the inner wall surface of the motor housing105. This space is utilized, for example, to provide an annular supporting part105A which is integrally formed with the inner wall of the motor housing105(or an annular member which is formed separately from the motor housing105) and supports the outer stator125B from outside. Specifically, according to this modification, the structure of supporting the outer circumferential region of the outer stator125B from outside by the supporting part105A of the motor housing105is provided in addition to the structure of supporting the outer circumferential region of the inner stator125A of the inner motor from outside by the motor housing105via the supporting member126. With this construction, the stator can be more firmly supported.

Further, according to this modification, the outer stator125B of the outer motor is disposed outside of the inner stator125A. Therefore, it can be constructed as shown in the drawing such that part127aof the bearing housing127A extends to the yoke125A1of the inner stator125A and supports the front surface of the yoke125A1. With this construction, the stator can be further more firmly supported.

(Seventh Embodiment of the Invention)

A seventh embodiment of the present invention is now described with reference toFIGS. 24 to 27. In this embodiment, as shown inFIGS. 24 and 25, the first internal gear133is constantly driven by the outer rotor123, and the first sun gear131can be driven and stopped by the inner rotor121. To this end, the outer rotor123is directly connected to the first internal gear133, and the bi-directional one-way clutch151is disposed between the inner rotor shaft121aof the inner rotor121and the first sun gear131. In the other points, this embodiment has the same construction as the above-described sixth embodiment, including the structure of supporting the outer circumferential region of the inner stator125A by the supporting member126. Therefore, components in this embodiment which are substantially identical to those in the sixth embodiment are given like numerals as in the sixth embodiment.

As shown inFIGS. 26 and 27, the bi-directional one-way clutch151has basically the same construction and function as that in the sixth embodiment (and thus the first embodiment). Due to arrangement of the bi-directional one-way clutch151between the inner rotor shaft121aand the first sun gear131, however, the fixed outer ring158which forms the outer shell of the bi-directional one-way clutch151is connected to the inside of the outer stator125B in front of the inner stator125A of the driving motor111and has a generally cup-like shape having a circular central opening through which the first sun gear131is loosely inserted. Further, four power transmitting parts153are disposed at predetermined intervals in the circumferential direction and integrally formed with a disc-like power transmitting member152. The power transmitting member152is connected to the inner rotor shaft121aand rotates together with the inner rotor shaft121a. The power receiving member157having the power receiving parts155is connected to the first sun gear131and rotates together with the first sun gear131. In the other points, the bi-directional one-way clutch151has the same construction as that in the sixth embodiment (and thus the first embodiment).

Therefore, when the inner rotor121is driven, as shown inFIG. 26, the lock pin159is pushed by the front end surface of the power transmitting part153in the rotation direction, so that each of the lock pins159is not wedged into a wedge-shaped space between the outer surface of the power receiving member157and the inner surface of the fixed outer ring158. Therefore, the power transmitting part153comes into contact with the power receiving part155in the circumferential direction and transmits torque to the first sun gear131. When torque is inputted from the output side to the input side, or more specifically when load is applied onto the first sun gear131(the spindle115) side and the power receiving member157is about to rotate with respect the power transmitting member152in the state shown inFIG. 27, the lock pins159are wedged into the wedge-shaped spaces between the outer surface of the power receiving member157and the inner surface of the fixed outer ring158, so that the power receiving member157is locked to the fixed outer ring158.

Specifically, when the inner rotor121on the input (driving) side is driven, the bi-directional one-way clutch151can transmit torque of the inner rotor121to the first sun gear131(the spindle115) on the output (driven) side both in the clockwise and counterclockwise directions. Moreover, when torque is about to be inputted reversely from the output side to the input side by load applied to the output side, the bi-directional one-way clutch151locks the first sun gear131and interrupts transmission of torque from the output side to the input side both in the clockwise and counterclockwise directions.

In this embodiment, the first internal gear133is constantly driven by the outer rotor123of the driving motor111, and the first sun gear131can be driven and stopped by the inner rotor121. Therefore, while the spindle115(the screw bit119) is driven by driving the outer rotor123, the inner rotor123is intermittently driven, or repeatedly alternates between driving and stopping. In this manner, the screw bit119which is being driven at an output torque outputted by the outer rotor123intermittently gains the output torque outputted by the inner rotor121. Thus, according to this embodiment, torque for driving the screw bit119can be intermittently changed.

Thus, according to this embodiment, by intermittently driving the inner rotor121, the operation of temporarily increasing the output torque to be outputted to the screw bit119and then immediately returning it to its initial state can be repeated. Therefore, for example, when load (tightening torque) increases upon seating of the screw on the workpiece during screw tightening operation, torque ripple can be caused by intermittently driving the inner rotor121, and the screw tightening operation can be performed at a higher tightening torque than a normal tightening torque.

Further, in this embodiment, the first sun gear131receives a reaction force when the screw bit119is rotationally driven by the outer rotor121. Therefore, the inner rotor121needs to generate higher torque than the outer rotor123in order to cause torque ripple by intermittent driving of the inner rotor123. During the time when torque ripple is not caused, the first sun gear131needs to be held in the locked state by stopping driving of the inner rotor121. If the first sun gear131is held in the locked state only by torque of the inner rotor121, motor burnout may be caused. According to this embodiment, however, the bi-directional one-way clutch151provided between the inner rotor121and the first sun gear131can interrupt reverse input of power from the first sun gear131on the driven side to the inner rotor121on the input side and hold the first internal gear133in the locked state. Thus, the outer rotor123can be protected from burnout.

Further, in this embodiment, a cooling fan163for cooling the motor is provided on the outer rotor123which is constantly driven. The cooling fan163is provided on the inner circumferential surface of an axial end (rear end) of the outer rotor123on the opposite side from the first internal gear133. The cooling fan163serves to cool the driving motor111by taking outside air into the space of the motor housing105through an inlet formed in the rear end of the motor housing105and leading it forward in the longitudinal direction. The air taken into the motor housing space cools the driving motor111by flowing into the motor through gaps between the outer stator125B and the outer rotor123and between the inner stator125A and the inner rotor121. Thereafter, the air flows out to the outside of the motor through a radially extending communication hole123a(seeFIG. 25) formed through a front end region of the outer rotor123. The air then further passes between the motor housing105and the gear housing107and is discharged to the outside through an outlet. In this case, preferably, the supporting member126for supporting the inner stator125A may be provided with air holes which extend through it in the longitudinal direction such that the cooling air can be led to the gap between the outer stator125B and the outer rotor123.

According to this embodiment, not only the above-described effects but the same effects as the first embodiment can be obtained, which are not described in order to avoid redundant description.

(Eighth Embodiment of the Invention)

An eighth embodiment of the present invention is now described with reference toFIGS. 28 and 29. In this embodiment, in the battery-powered screwdriver101, the first sun gear131of the planetary gear mechanism113is driven by the inner rotor121to rotationally drive the spindle115(the screw bit119) via the planetary gear mechanism113, while a cooling fan165is driven by the outer rotor123. In the other points, this embodiment has generally the same construction as the sixth embodiment, except that the bi-directional one-way clutch151is not provided and the first and second internal gears133,141are formed in one piece and fixed to the gear housing107side in the planetary gear mechanism113and further that the outer circumferential region of the inner stator125A is supported by the supporting member126. Therefore, components in this embodiment which are substantially identical to those in the sixth embodiment are given like numerals as in the sixth embodiment, and they are not described.

A cylindrical fan housing part124is formed on one (front) end of the outer rotor123in the longitudinal direction and extends forward of the front ends of the outer stator125B and the inner rotor121(toward the planetary gear mechanism113). The cooling fan165for cooling the motor is housed and fixed within the fan housing part124. The fan housing part124is a feature that corresponds to the “extending region”, and the cooling fan165is a feature that corresponds to the “actuating member other than the tool bit” and the “fan” according to this invention.

In this embodiment, the electric current value of the driving motor111is monitored. When the amount of heat generation of the driving motor111is small, for example, under no load, the cooling fan165is stopped, and when the amount of heat generation of the driving motor111is large, for example, during operation, the outer rotor123is driven to drive the cooling fan165.

According to this embodiment, independently of driving of the spindle115by the inner rotor121, the cooling fan165can be driven by the outer rotor123. Therefore, regardless of the operational status of the spindle115(the screw bit119), the cooling fan165can be constantly driven at the maximum speed. Therefore, the effect of cooling the driving motor111can be improved, so that the driving motor111can be protected from burnout.

Further, the inner rotor121is exclusively used for driving the spindle115and not used for driving the cooling fan165. Accordingly, the output of the inner rotor121is improved. Further, when the amount of heat generation of the driving motor111is small, the cooling fan165can be stopped, so that generation of noise can be lessened.

Further, according to this embodiment, with the construction in which the motor is arranged coaxially with the output shaft or the spindle115, the inner rotor121, the inner and outer stators125A,125B and the outer rotor123can be simultaneously cooled by the one cooling fan165, and the relatively large cooling fan can be mounted without increasing the size of the machine body. Thus, the cooling effect can be easily obtained.

(Ninth Embodiment of the Invention)

A ninth embodiment of the present invention is now described with reference toFIG. 30. This embodiment is a modification to the eighth embodiment and different from the eighth embodiment in that, in addition to the motor cooling fan165mounted to the outer rotor123, a cooling fan167for cooling the motor is mounted to the inner rotor121. In the other points, this embodiment has the same construction as the above-described eighth embodiment. The cooling fan167to be driven by the inner rotor121is provided rearward of the rear end surface of the inner stator125A on the rear end of the inner rotor121. Each of the cooling fans165,167is a feature that corresponds to the “actuating member other than the tool bit” and the “fan” according to this invention.

Therefore, according to the ninth embodiment, the motor is cooled by the cooling fan167even during normal operation in which the spindle115is rotationally driven by driving the inner rotor121. Thus, the operating time of the outer rotor123can be shortened.

Further, the electric current value of the driving motor111is monitored. Under high load or other similar conditions in which the motor may easily burn out, the cooling fan165can be driven by the outer rotor123so that the cooling capacity can be improved. Therefore, this embodiment can be suitably applied to a tightening tool which is used under relatively high-load conditions. Further, the cooling fan165which is driven by the outer rotor123is used only under high-load conditions, so that the amount of screw tightening operation per charge can be easily ensured.

Further, like in the fourth embodiment, with the construction in which the motor is arranged coaxially with the output shaft or the spindle115, the relatively large cooling fan can be mounted without increasing the size of the machine body. Thus, the cooling effect can be easily obtained.

Further, it can be constructed such that a dust collecting fan, which is not shown, is driven by one or both of the inner rotor121and the outer rotor123. For example, in some cases, a dust collecting device is provided to collect dust which is generated during drilling operation on a workpiece with a drill bit coupled to the spindle115. The dust collecting fan is provided as a suction force generating means for sucking dust generated by the drilling operation. Therefore, by provision of the construction in which the suction force generating means in the form of the dust collecting fan is driven by one or both of the inner rotor121and the outer rotor123, the power tool with a dust collecting device can be rationally provided.

In the above-described embodiments, the screwdriver is explained as a representative example of the power tool, but the present invention may be applied not only to a fastening tool for fastening screws or the like, but to a drill for drilling operation, a hammer and a hammer drill for chipping operation and drilling operation, and a circular saw and an electric cutter for cutting operation in wood or metal working.

DESCRIPTION OF NUMERALS