Power tool

Disclosed is a striking tool technology that contributes to reducing clutch sizes. The striking tool causes a tool bit to perform a striking operation in the long axis direction and to perform a rotational operation about the long axis, thereby causing the tool bit to carry out a predetermined machining operation. The striking tool comprises a tool body; a motor which is housed in the tool body and drives the tool bit; and a clutch which, on a route where the torque of the motor is transmitted to the tool bit, is disposed in a high rotational speed and low torque region that is a stage prior to where the rotational speed of the motor is reduced, which transmits the torque of the motor to the tool bit in a normal state, and which cuts off the transmission of torque generated about the tool bit long axis in the tool body if the torque exceeds a predetermined torque level.

FIELD OF THE INVENTION

The present invention relates to an impact power tool which is capable of preventing excessive reaction torque from acting on a tool body when a tool bit is unintentionally locked.

BACKGROUND OF THE INVENTION

U.S. Patent Publication No. 2007-0289759 discloses a hammer drill having a clutch which is disposed in a power transmitting mechanism for transmitting torque of a motor to a tool bit and capable of interrupting torque transmission from the motor to the tool bit when the hammer bit is unintentionally locked during hammer drill operation and thereby preventing reaction torque or excessive torque from acting on a tool body in a direction opposite to the direction of rotation of the tool bit.

In the above-described known technique for preventing reaction torque, the clutch is disposed in the power transmitting mechanism in which the rotation speed of the motor is reduced. Therefore, the size of the clutch is increased in order to allow transmission of high torque. In this point, further improvement is required.

DISCLOSURE OF THE INVENTION

Problems to be Solved by the Invention

Accordingly, it is an object of the present invention to provide an impact tool that contributes to size reduction of a clutch.

Means for Solving the Problems

In order to solve the above-described problem, according to a preferred embodiment of the present invention, an impact tool is provided which causes a tool bit to perform striking movement in its axial direction and rotation around its axis and thereby causes the tool bit to perform a predetermined operation on a workpiece.

The impact tool according to the preferred embodiment of the present invention includes a tool body, a motor that is housed in the tool body and drives the tool bit, a clutch that is disposed in a high-speed low-torque region located at a stage prior to reduction of rotation speed of the motor in a path of transmitting torque of the motor to the tool bit, and normally transmits torque of the motor to the tool bit, while interrupting the torque transmission when the torque acting on the tool body around an axis of the tool bit exceeds a predetermined torque.

The “torque acting on the tool body around an axis of the tool bit” refers to reaction torque which acts on the tool body in a direction opposite to the direction of rotation of the tool bit during operation. Further, the “predetermined torque” acting on the tool body can be recognized by using a method of measuring torque values of a shaft rotating together with the tool bit in the power transmitting path, via a torque sensor and determining from the measurement whether the torque exceeds the predetermined torque, or by using a method of measuring momentum of the tool body around an axis of the tool bit via a speed sensor or an acceleration sensor and determining from the measurements whether the torque exceeds the predetermined torque value.

According to this invention having the above-described construction, when the tool bit is unintentionally locked during operation such as drilling on a workpiece, the clutch can interrupt torque transmission between the motor and the tool bit and thereby prevent excessive reaction torque from acting on the tool body. Particularly, according to this invention, with the construction in which the clutch is disposed in a high-speed low-torque region located at a stage prior to reduction of rotation speed of the motor, torque acting on the clutch is reduced, so that the clutch can be reduced in size and weight.

According to a further embodiment of the present invention, in the path of transmitting torque of the motor to the tool bit, the impact tool includes a motor output shaft, a power transmitting shaft which is disposed downstream of the motor output shaft and reduces the speed of rotation of the motor output shaft and transmits the rotation to the tool bit, and a clutch shaft disposed between the motor output shaft and the power transmitting shaft. Further, the clutch is disposed on the clutch shaft.

According to this invention, when the tool bit is unintentionally locked during operation such as drilling on a workpiece, the clutch can interrupt torque transmission between the motor and the tool bit and thereby prevent excessive reaction torque from acting on the tool body. Particularly, according to this invention, the clutch shaft is disposed between the motor output shaft and the power transmitting shaft which reduces the speed of rotation of the motor output shaft and transmits the rotation, and the clutch is disposed on the clutch shaft. Specifically, in this invention, a shaft specifically designed for mounting the clutch is provided. With such a construction, the degree of freedom in designing the clutch increases, and the clutch can be driven at high speed and low torque. Thus, torque acting on the clutch is reduced, so that the clutch can be reduced in size and weight.

According to a further embodiment of the present invention, the speed ratio between the motor output shaft and the clutch shaft is smaller than the speed reducing ratio between the clutch shaft and the power transmitting shaft.

According to this invention, the speed ratio between the motor output shaft and the clutch shaft can be arbitrarily selected to equal, decrease or increase the speed.

According to a further embodiment of the present invention, the impact tool further includes a striking element that is rectilinearly driven by the motor in the axial direction of the tool bit and strikes the tool bit in the axial direction. Further, the clutch is disposed closer to an axis of striking movement of the striking element than a power transmitting region between the clutch shaft and the power transmitting shaft. The “power transmitting region” typically refers to a power transmitting region for transmitting power by engagement between gears on the shafts.

According to this invention, with the construction in which the clutch is disposed closer to the axis of striking movement of the striking element, moment (vibration) which is caused in the striking direction around the center of gravity of the impact tool during striking movement of the tool bit can be effectively reduced.

According to a further embodiment of the present invention, the clutch includes a driving-side clutch part and a driven-side clutch part, and transmits torque by contact of the clutch parts while interrupting the torque transmission by disengagement of the clutch parts. Further, the clutch shaft includes a driving-side clutch shaft formed on the driving-side clutch part and a driven-side clutch shaft formed on the driven-side clutch part, and the clutch shafts are coaxially disposed radially inward and outward.

According to this invention, clutch faces (power transmitting faces) of the clutch can be provided on the same shaft end region. Specifically, input and output can be made on the same shaft end region, so that the clutch can be disposed closer to the axis of striking movement. Further, the clutch can be reduced in size in its axial direction, so that rational space-saving arrangement can be realized.

According to a further embodiment of the present invention, in the path of transmitting torque of the motor to the tool bit, the impact tool includes an impact drive mechanism for driving the tool bit by impact, a rotary drive mechanism for rotationally driving the tool bit, an impact drive shaft that is rotationally driven by the motor and normally drives the impact drive mechanism, and a rotary drive shaft that is rotationally driven independently of the impact drive shaft by the motor and drives the rotary drive mechanism. Further, the impact drive shaft and the rotary drive shaft are coaxially disposed, and the clutch is disposed on the rotary drive shaft.

According to this invention, when the tool bit is unintentionally locked during operation such as drilling on a workpiece, the clutch can interrupt torque transmission between the motor and the rotary drive mechanism and thereby prevent excessive reaction torque from acting on the tool body. Particularly, according to this invention, with the construction in which the clutch is disposed on the rotary drive shaft which is driven at high speed and low torque of the motor, torque acting on the clutch is reduced and the clutch can be reduced in size and weight.

According to a further embodiment of the present invention, in the impact tool in which the impact drive shaft and the rotary drive shaft are coaxially disposed and the clutch is disposed on the rotary drive shaft, the impact drive shaft is located radially inward and the rotary drive shaft is located radially outward. According to this invention, size reduction in the axial direction can be realized, so that rational space-saving arrangement can be achieved.

According to a further embodiment of the present invention, the clutch is designed and provided as an electromagnetic clutch including a driving-side clutch part, a driven-side clutch part, a biasing member that biases the clutch parts away from each other so as to interrupt transmission of torque, and an electromagnetic coil that brings the clutch parts into contact with each other against the biasing force of the biasing member and thereby transmits torque when the electromagnetic coil is energized.

According to this invention, by utilizing the electromagnetic clutch as a clutch for preventing excessive reaction torque from acting on the tool body, the clutch can be made easy to control and reduced in size.

According to a further embodiment of the present invention, torque transmission between shafts in the torque transmission path of transmitting torque from the motor to the tool bit is made by a gear, and the gear is housed in a gear chamber in which a lubricant is sealed. Further, the clutch is isolated from the gear chamber. According to this invention, with the construction in which the clutch is isolated from the gear chamber or from the lubricant, an occurrence of slippage by the lubricant can be avoided. Therefore, a friction clutch having a high reaction rate can be used as the clutch.

According to a further embodiment of the present invention, components of an impact drive mechanism that is driven by the motor and drives the tool bit by impact and components of a rotary drive mechanism that is driven by the motor and rotationally drives the tool bit are provided independently of each other.

Effect of the Invention

According to this invention, an impact tool is provided which contributes to size reduction of a clutch. 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 OF 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 provide and manufacture improved impact tools and methods for using such impact tools and devices utilized therein. Representative examples of the present invention, which examples utilized many of these additional features and method steps in conjunction, will now be 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

A first embodiment of the present invention is now described with reference toFIGS. 1 to 5. The first embodiment corresponds to claim1of the invention. In this embodiment, an electric hammer drill is explained as a representative example of the impact tool. As shown inFIGS. 1 and 2, the hammer drill101according to this embodiment mainly includes a body103that forms an outer shell of the hammer drill101, a hammer bit119detachably coupled to a front end region (on the left as viewed inFIG. 1) of the body103via a hollow tool holder137, and a handgrip109designed to be held by a user and connected to the body103on the side opposite to the hammer bit119. The hammer bit119is held by the tool holder137such that it is allowed to linearly move with respect to the tool holder in its axial direction. The body103and the hammer bit119are features that correspond to the “tool body” and the “tool bit”, respectively, according to the present invention. In this embodiment, for the sake of convenience of explanation, the side of the hammer bit119is taken as the front and the side of the handgrip109as the rear.

The body103includes a motor housing105that houses a driving motor111, and a gear housing107that houses a motion converting mechanism113, a striking mechanism115and a power transmitting mechanism117. The driving motor111is arranged such that its rotation axis runs in a vertical direction (vertically as viewed inFIG. 1) substantially perpendicular to a longitudinal direction of the body103(the axial direction of the hammer bit119). The motion converting mechanism113appropriately converts torque (rotating output) of the driving motor111into linear motion and then transmits it to the striking mechanism115. Then, an impact force is generated in the axial direction of the hammer bit119(the horizontal direction as viewed inFIG. 1) via the striking mechanism115. The driving motor111is a feature that corresponds to the “motor” according to this invention. The motion converting mechanism113and the striking mechanism115are features that correspond to the “impact drive mechanism” according to this invention.

Further, the power transmitting mechanism117appropriately reduces the rotational speed outputted by the driving motor111and transmits the reduced rotational speed to the hammer bit119via the tool holder137, so that the hammer bit119is caused to rotate in its circumferential direction. The driving motor111is driven when a user depresses a trigger109adisposed on the handgrip109. The power transmitting mechanism117is a feature that corresponds to the “rotary drive mechanism” according to this invention.

As shown inFIG. 3, the motion converting mechanism113mainly includes a first driving gear121that is formed on an output shaft (rotating shaft)111aof the driving motor111and caused to rotate in a horizontal plane, a driven gear123that engages with the first driving gear121, a crank shaft122to which the driven gear123is fixed, a crank plate125that is caused to rotate in a horizontal plane together with the crank shaft122, a crank arm127that is loosely connected to the crank plate125via an eccentric shaft126, and a driving element in the form of a piston129which is mounted to the crank arm127via a connecting shaft128. The output shaft111aof the driving motor111and the crank shaft122are disposed side by side in parallel to each other. The crank shaft122, the crank plate125, the eccentric shaft126, the crank arm127and the piston129form a crank mechanism. The piston129is slidably disposed within a cylinder141. When the driving motor111is driven, the piston129is caused to linearly move in the axial direction of the hammer bit119along the cylinder141.

The striking mechanism115mainly includes a striking element in the form of a striker143slidably disposed within the bore of the cylinder141, and an intermediate element in the form of an impact bolt145that is slidably disposed within the tool holder137and serves to transmit kinetic energy of the striker143to the hammer bit119. An air chamber141ais formed between the piston129and the striker143in the cylinder141. The striker143is driven via pressure fluctuations (air spring action) of the air chamber141aof the cylinder141by sliding movement of the piston129. The striker143then collides with (strikes) the impact bolt145which is slidably disposed in the tool holder137. As a result, a striking force caused by the collision is transmitted to the hammer bit119via the impact bolt145. Specifically, the motion converting mechanism113and the striking mechanism115for driving the hammer bit119by impact are directly connected to the driving motor111.

The power transmitting mechanism117mainly includes a second driving gear131, a first intermediate gear132, a first intermediate shaft133, an electromagnetic clutch134, a second intermediate gear135, a mechanical torque limiter147, a second intermediate shaft136, a small bevel gear138, a large bevel gear139and the tool holder137. The power transmitting mechanism117transmits torque of the driving motor111to the hammer bit119. The second driving gear131is fixed to the output shaft111aof the driving motor111and caused to rotate in the horizontal plane together with the first driving gear121. The first and second intermediate shafts133,136are located downstream from the output shaft111ain terms of torque transmission and disposed side by side in parallel to the output shaft111a. The first intermediate shaft133is provided as a shaft for mounting the clutch and disposed between the output shaft111aand the second intermediate shaft136. The first intermediate shaft133is rotated via the electromagnetic clutch134by the first intermediate gear132which is constantly engaged with the second driving gear131. The speed ratio of the first intermediate gear132to the second driving gear131is set to be almost the same. The second intermediate shaft136and the output shaft111aof the driving motor111are features that correspond to the “power transmitting shaft” and the “motor output shaft”, respectively, according to this invention.

The electromagnetic clutch134serves to transmit torque or interrupt torque transmission between the driving motor111and the hammer bit119or between the output shaft111aand the second intermediate shaft136. Specifically, the electromagnetic clutch134is disposed on the first intermediate shaft133and serves to prevent the body103from being swung when the hammer bit119is unintentionally locked and reaction torque acting on the body103excessively increases. The electromagnetic clutch134is disposed above the first intermediate gear132in the axial direction of the first intermediate shaft133and located closer to the axis of motion (axis of striking movement) of the striker143than the first intermediate gear132. The electromagnetic clutch134is a feature that corresponds to the “clutch” according to this invention. Specifically, the power transmitting mechanism117for rotationally driving the hammer bit119is constructed to transmit torque of the driving motor111or interrupt the torque transmission via the electromagnetic clutch134.

As shown inFIGS. 4 and 5, the electromagnetic clutch134mainly includes a circular cup-shaped driving-side rotating member161and a disc-like driven-side rotating member163which are opposed to each other in their axial direction, a biasing member in the form of a spring disc167which constantly biases the driving-side rotating member161in a direction that releases engagement (frictional contact) between the driving-side rotating member161and the driven-side rotating member163, and an electromagnetic coil165that engages the driving-side rotating member161with the driven-side rotating member163when it is energized. The driving-side rotating member161and the driven-side rotating member163are features that correspond to the “driving-side clutch part” and the “driven-side clutch part”, respectively, according to this invention.

The driving-side rotating member161has a shaft (boss)161aprotruding downward. The shaft161ais fitted onto the first intermediate shaft133and can rotate around its axis with respect to the first intermediate shaft133. Further, the first intermediate gear132is fixedly mounted on the shaft161a. Therefore, the driving-side rotating member161and the first intermediate gear132rotate together. The driven-side rotating member163also has a shaft (boss)163aprotruding downward and the shaft163ais integrally fixed on one axial end (upper end) of the first intermediate shaft133. Thus, the driven-side rotating member163can rotate with respect to the driving-side rotating member161. When the first intermediate shaft133integrated with the shaft163aof the driven-side rotating member163is viewed as part of the shaft163a, the shaft163aand the shaft161aof the driving-side rotating member161are coaxially disposed radially inward and outward. Specifically, the shaft163aof the driven-side rotating member163is disposed radially inward, and the shaft161aof the driving-side rotating member161is disposed radially inward. The shaft161aof the driving-side rotating member161is a feature that corresponds to the “driving-side clutch shaft” and the shaft163aof the driven-side rotating member163and the first intermediate shaft133are features that correspond to the “driven-side clutch shaft” according to this invention.

Further, the driving-side rotating member161is divided into a radially inner region162aand a radially outer region162b, and the inner and outer regions162a,162bare connected by the spring disc167and can move in the axial direction with respect to each other. The outer region162bis provided and configured as a movable member which comes into frictional contact with the driven-side rotating member163. In the electromagnetic clutch134having the above-described construction, the outer region162bof the driving-side rotating member161is displaced in the axial direction by energization or de-energization of the electromagnetic coil165based on a command from a controller157. Torque is transmitted to the driven-side rotating member163when the electromagnetic clutch134comes into engagement (frictional contact) with the driven-side rotating member163(seeFIG. 5), while the torque transmission is interrupted when this engagement is released (seeFIG. 4).

Further, as shown inFIG. 3, the second intermediate gear135is fixed on the other axial end (lower end) of the first intermediate shaft133, and torque of the second intermediate gear135is transmitted to the second intermediate shaft136via the mechanical torque limiter147. The mechanical torque limiter147is provided as a safety device against overload on the hammer bit119and interrupts torque transmission to the hammer bit119when excessive torque exceeding a set value (hereinafter also referred to as a maximum transmission torque value) acts upon the hammer bit119. The mechanical torque limiter147is coaxially mounted on the second intermediate shaft136.

The mechanical torque limiter147includes a driving-side member148having a third intermediate gear148awhich is engaged with the second intermediate gear135, and a hollow driven-side member149which is loosely fitted on the second intermediate shaft136. Further, in one axial end region (lower end region as viewed inFIG. 3) of the driven-side member149, teeth149aand136aformed in the driven-side member149and the second intermediate shaft136are engaged with each other. With such a construction, the mechanical torque limiter147and the second intermediate shaft136are caused to rotate together. The speed ratio of the third intermediate gear148aof the driving-side member148to the second intermediate gear135is set such that the third intermediate gear148arotates at a reduced speed compared with the second intermediate gear135. Although not particularly shown, when the torque acting on the second intermediate shaft136(which corresponds to the torque acting on the hammer bit119) is lower than or equal to the maximum transmission torque value which is preset by a spring147a, torque is transmitted between the driving-side member148and the driven-side member149. However, when the torque acting on the second intermediate shaft136exceeds the maximum transmission torque value, torque transmission between the driving-side member148and the driven-side member149is interrupted.

Further, torque transmitted to the second intermediate shaft136is transmitted at a reduced rotation speed from a small bevel gear138which is integrally formed with the second intermediate shaft136, to a large bevel gear139which is rotated in a vertical plane in engagement with the small bevel gear138. Moreover, torque of the large bevel gear139is transmitted to the hammer bit119via a final output shaft in the form of the tool holder137which is connected to the large bevel gear139.

In the motion converting mechanism113and the power transmitting mechanism117, gears which need lubricating are housed within a closed gear housing space107aof the gear housing107in which a lubricant is sealed. The gear housing space107ais a feature that corresponds to the “gear chamber” according to this invention. In this embodiment, by provision for the electromagnetic clutch134that transmits torque by frictional contact between the driving-side rotating member161and the driven-side rotating member163, slippage may be caused if the lubricant adheres to the clutch face.

Therefore, in this embodiment, a clutch housing space107bseparated from the gear housing space107ais provided within the gear housing107, and the electromagnetic clutch134is housed within the clutch housing space107bsuch that it is isolated from the gear housing space107a. As shown inFIGS. 4 and 5, the clutch housing space107bis defined by a generally inverted cup-shaped inner housing108aand integrally formed with the gear housing107therein, and a covering member108bpress-fitted into an opening of the inner housing108afrom below. The first intermediate shaft133and the shaft161aof the driving-side rotating member161extend downward (into the gear housing space107a) through the center of the covering member108b. Due to this construction, a clearance is formed between the outer surface of the shaft161aand the inner circumferential surface of the covering member108b. The clearance is however closed by a bearing169disposed between the outer surface of the shaft161aand the inner circumferential surface of the covering member108b. Specifically, the bearing169is utilized as a sealing member and prevents the lubricant from entering the clutch housing space107b.

Further, as shown inFIG. 3, a non-contact magnetostrictive torque sensor151is installed in the power transmitting mechanism117and serves to detect torque acting on the hammer bit119during operation. The magnetostrictive torque sensor151serves to measure torque acting on the driven-side member149of the mechanical torque limiter147in the power transmitting mechanism117. The magnetostrictive torque sensor151has an exciting coil153and a detecting coil155around an inclined groove formed in an outer circumferential surface of a torque detecting shaft in the form of the driven-side member149. In order to measure the torque, the magnetostrictive torque sensor151detects change in magnetic permeability of the inclined groove of the driven-side member149as a voltage change by the detecting coil155when the driven-side member149is turned.

A torque value measured by the magnetostrictive torque sensor151is outputted to the controller157. When the torque value outputted from the magnetostrictive torque sensor151exceeds a predetermined torque setting, the controller157outputs a de-energization command to the electromagnetic coil165of the electromagnetic clutch134to disengage the electromagnetic clutch134. Further, as for the torque setting at which the controller157executes disengagement of the electromagnetic clutch134, a user can arbitrarily change (adjust) the torque setting by externally manually operating a torque adjusting means (for example, a dial), which is not shown. The torque setting adjusted by the torque adjusting means is limited to within a range lower than the maximum transmission torque value set by the spring147aof the mechanical torque limiter147. The controller157forms a clutch controlling device.

Further, in this embodiment, the electromagnetic clutch134provided for preventing excessive reaction torque from acting on the body103also serves as a clutch for switching between operation modes, or between hammer drill mode in which the hammer bit119is caused to perform striking movement and rotation and hammer mode in which the hammer bit119is caused to perform only striking movement, which is explained below in further detail.

As shown inFIGS. 1 and 2, an operation mode switching member in the form of an operation mode switching lever171is disposed in an upper surface region of the body103. The operation mode switching lever171is a disc-like member having an operation tab, and mounted to the body103such that it can rotate around its vertical axis perpendicular to the axis of the hammer bit119, so that it can be turned 360 degrees in a horizontal plane. A position sensor173for detecting operation mode is provided in the body103. When the position sensor173detects the position of the operation mode switching lever171, or specifically a part to be detected175which is provided in the operation mode switching lever171, its detection signal is inputted to the controller157.

The controller157outputs an energization command to the electromagnetic coil165of the electromagnetic clutch134when the position sensor173detects the part to be detected175and its detection signal is inputted to the controller157, while the controller157outputs a de-energization command to the electromagnetic coil165when the position sensor173does not detect the part to be detected175. In this embodiment, the position sensor173detects the part to be detected175only when the user selects hammer drill mode by turning the operation mode switching lever171and does not otherwise detect it.

The electric hammer drill101according to this embodiment is constructed as described above. Operation and usage of the hammer drill101is now explained. When the user turns the operation mode switching lever171to the hammer mode position (as shown inFIG. 1, an arrow marked on the operation mode switching lever171is aligned with a hammer mode mark M1marked on the body103), the position sensor173does not detect the part to be detected175in the operation mode switching lever171. At this time, the electromagnetic coil165of the electromagnetic clutch134is de-energized by a de-energization command from the controller157. Thus, an electromagnetic force is no longer generated, so that the outer region162bof the driving-side rotating member161is separated from the driven-side rotating member163by the biasing force of the spring disc167. Specifically, the electromagnetic clutch134is switched to the torque transmission interrupted state (seeFIGS. 1 and 4).

In this state, when the trigger109is depressed in order to drive the driving motor111, the piston129is caused to rectilinearly slide along the cylinder141via the motion converting mechanism113. By this sliding movement, the striker143is caused to rectilinearly move within the cylinder141via air pressure fluctuations or air spring action in the air chamber141aof the cylinder141. The striker143then collides with the impact bolt145, so that the kinetic energy caused by this collision is transmitted to the hammer bit119. Specifically, when the hammer mode is selected, the hammer bit119performs hammering movement in the axial direction so that a hammering (chipping) operation is performed on a workpiece.

When the operation mode switching lever171is turned to the hammer drill mode position (as shown inFIG. 2, the arrow on the operation mode switching lever171is aligned with a hammer drill mode mark M2), the position sensor173detects the part to be detected175in the operation mode switching lever171. At this time, the electromagnetic coil165is energized by an energization command from the controller157, and an electromagnetic force is generated so that the outer region162bof the driving-side rotating member161is pressed onto the driven-side rotating member163against the biasing force of the spring disc167. Specifically, the electromagnetic clutch134is switched to the torque transmission state (seeFIGS. 2 and 5).

In this state, when the trigger109is depressed in order to drive the driving motor111, the rotating output of the driving motor111is transmitted to the tool holder137via the power transmitting mechanism117. Thus, the hammer bit119held by the tool holder137is rotated around its axis. Specifically, when the hammer drill mode is selected, the hammer bit119performs hammering movement in its axial direction and drilling movement in its circumferential direction, so that a hammer drill operation (drilling operation) is performed on a workpiece.

During the above-described hammer drill operation, the magnetostrictive torque sensor151measures the torque acting on the driven-side member149of the mechanical torque limiter147and outputs it to the controller157. When the hammer bit119is unintentionally locked for any cause and the measured torque value inputted from the magnetostrictive torque sensor151to the controller157exceeds the torque setting preset by the user, the controller157outputs a command of de-energization of the electromagnetic coil165to disengage the electromagnetic clutch134. Therefore, the electromagnetic coil165is de-energized and thus the electromagnetic force is no longer generated, so that the outer region162bof the driving-side rotating member161is separated from the driven-side rotating member163by the biasing force of the spring disc167. Specifically, the electromagnetic clutch134is switched from the torque transmission state to the torque transmission interrupted state, so that the torque transmission from the driving motor111to the hammer bit119is interrupted. Thus, the body103can be prevented from being swung by excessive reaction torque acting on the body103due to locking of the hammer bit119. The above-described torque setting is a feature that corresponds to the “predetermined torque” according to this invention.

As described above, in this embodiment, as for the structure of transmitting torque of the driving motor111, the electromagnetic clutch134is disposed in a rotary drive path of the hammer bit119. Thus, the impact driving structure is configured to be directly connected to the driving motor and only rotation is transmitted via the electromagnetic clutch134. Therefore, compared with a construction in which a clutch is disposed to transmit torque of the driving motor111to both the impact drive line and the rotation drive line, torque acting on the electromagnetic clutch134is reduced, so that the electromagnetic clutch134can be reduced in size and weight. Further, according to this embodiment, the first intermediate shaft133is specifically designed for mounting a clutch and the electromagnetic clutch134is provided on the first intermediate shaft133. With this construction, the electromagnetic clutch134can be provided in a high-speed low-torque region located at a stage prior to reduction of rotation speed of the driving motor111(the output shaft111a). Therefore, the degree of freedom in designing the electromagnetic clutch134increases, so that further size reduction can be realized.

Further, according to this embodiment, in the electromagnetic clutch134, the shaft161aof the driving-side rotating member161is rotatably fitted onto the first intermediate shaft133on which the shaft163aof the driven-side rotating member163is fixed. Specifically, the first intermediate shaft133, the shaft161aof the driving-side rotating member161and the shaft163aof the driven-side rotating member163form a clutch shaft of the electromagnetic clutch134, and the driving-side member and the driven-side member are coaxially disposed radially inward and outward. With this construction, the clutch faces (power transmitting faces) of the electromagnetic clutch134can be provided on the same shaft end (upper end) region. Specifically, input and output can be made on the same shaft end region, so that the electromagnetic clutch134can be disposed closer to the axis of motion (axis of striking movement) of the striker143. As a result, moment (vibration) which is caused in the striking direction around the center of gravity in the body103during operation can be reduced, and the electromagnetic clutch134can be reduced in size in its axial direction.

Further, in this embodiment, the electromagnetic clutch134is disposed above the power transmitting region in which torque is transmitted between the first intermediate shaft133and the second intermediate shaft136, or the engagement region in which the second intermediate gear135is engaged with the third intermediate gear148aof the driving-side member148of the mechanical torque limiter147. With this construction, the electromagnetic clutch134can be disposed further closer to the axis of motion (axis of striking movement) of the striker143, which is more advantageous in reducing moment (vibration) in the striking direction.

Further, in this embodiment, the clutch housing space107bseparated from the gear housing space107ais provided within the gear housing107, and the electromagnetic clutch134is housed within the clutch housing space107bsuch that it is isolated from the gear housing space107a. Therefore, the electromagnetic clutch134has no risk of slippage by contact of its clutch face with the lubricant, so that a friction clutch having a high reaction rate can be used as the electromagnetic clutch134. Further, in this embodiment, by provision of the construction in which the electromagnetic clutch134is switched between the torque transmission state and the torque transmission interrupted state by displacement of part (only the outer region162b) of the driving-side rotating member161in its axial direction, the movable part can be reduced so that the clutch can be made easier to design.

Further, in this embodiment, the electromagnetic clutch134provided for preventing excessive reaction torque from acting on the body103also serves as a clutch for switching between operation modes, or between hammer mode in which the hammer bit119is caused to perform only striking movement and hammer drill mode in which the hammer bit119is caused to perform striking movement and rotation. With this construction, a rational design for preventing excessive reaction torque from acting on the body103and switching between operation modes can be realized.

Second Embodiment

A second embodiment of the present invention is now described with reference toFIGS. 6 and 7. This embodiment is a modification to the arrangement of the electromagnetic clutch134and corresponds to claim2of the invention. In this embodiment, the electromagnetic clutch134is disposed on the output shaft111aof the driving motor111.

As shown inFIG. 7, the electromagnetic clutch134includes a driving-side rotating member181and a driven-side rotating member183which are opposed to each other in its axial direction. A shaft (boss)181aof the driving-side rotating member181is integrally fixed on the output shaft111a, and a shaft (boss)183aof the driven-side rotating member183is rotatably fitted onto the output shaft111a. Further, the driven-side rotating member183is disposed above the driving-side rotating member181.

The driven-side rotating member183is divided into a radially inner region182aand a radially outer region182b, and the inner and outer regions182a,182bare connected by a spring disc187and can move in the axial direction with respect to each other. The outer region182bis provided and configured as a member which comes into engagement (frictional contact) with the driving-side rotating member181. Specifically, in this embodiment, the outer region182bof the driven-side rotating member183is displaced in the axial direction via the spring disc187. When an electromagnetic coil185is de-energized, the outer region182bis biased by the spring disc187such that it is separated from the driving-side rotating member181, and when the electromagnetic coil185is energized, the outer region182bcomes into engagement (frictional contact) with the driving-side rotating member181by the electromagnetic force.

The first driving gear121is formed on the upper end of the output shaft111aand engaged with the driven gear123of the crank mechanism which forms the motion converting mechanism113. Specifically, the motion converting mechanism113and the striking mechanism115for driving the hammer bit119by impact are directly connected to the driving motor111. In this point, this embodiment is similar to the first embodiment. The motion converting mechanism113and the striking mechanism115are features that correspond to the “impact drive mechanism”, and the output shaft111ais a feature that corresponds to the “impact drive shaft” according to this invention.

The shaft183aof the driven-side rotating member183extends upward and a second driving gear191is fixed on the extending end of the shaft183a. Further, a first intermediate shaft193is disposed between the output shaft111aand the second intermediate shaft136of the power transmitting mechanism117which is disposed side by side in parallel to the output shaft111aand in parallel to the shafts111a,136. A first intermediate gear195is fixed on one axial end (lower end) of the first intermediate shaft193and engaged with the second driving gear191, and a second intermediate gear197is fixed on the other axial end (upper end) of the first intermediate shaft193. The second intermediate gear197is engaged with the third intermediate gear148aof the driving-side member148of the mechanical torque limiter147provided on the second intermediate shaft136. The electromagnetic clutch134disposed on the output shaft111aof the driving motor111transmits torque or interrupt torque transmission between the output shaft111aand the first intermediate shaft193. Specifically, the power transmitting mechanism117for rotationally driving the hammer bit119is constructed to transmit torque of the driving motor111or interrupt the torque transmission via the electromagnetic clutch134. The power transmitting mechanism117is a feature that corresponds to the “rotary drive mechanism” according to this invention. Further, the shaft181aof the driving-side rotating member181and the shaft183aof the driven-side rotating member183form a clutch shaft, and the clutch shaft is a feature that corresponds to the “rotary drive shaft” according to this invention.

Further, the electromagnetic clutch134is housed within the clutch housing space107bof the gear housing107so that it is isolated from the gear housing space107a. The clutch housing space107bis defined by the inner housing108aformed (fixed separately) on the gear housing107and the covering member108bwhich serves as a partition to separate the inner space of the inner housing108afrom the gear housing space107a.

In the electromagnetic clutch134, the shaft183aof the driven-side rotating member183extends from the clutch housing space107binto the gear housing space107a. Due to this construction, clearances are formed between the outer circumferential surface of the shaft183aand the inner circumferential surface of the covering member108band between the inner circumferential surface of the shaft183aand the outer circumferential surface of the output shaft111a. The clearances are however closed by a bearing198disposed between the outer circumferential surface of the shaft183aand the inner circumferential surface of the covering member108band a bearing199disposed between the inner circumferential surface of the shaft183aand the outer circumferential surface of the output shaft111a. Specifically, the bearings198,199are utilized as a sealing member and prevent the lubricant from entering the clutch housing space107b.

In the other points, including the structure for engagement and disengagement (torque transmission and interruption) of the electromagnetic clutch134based on measurements of torque by the magnetostrictive torque sensor151, and the structure for engagement and disengagement of the electromagnetic clutch134based on switching operation of the operation mode switching lever171, 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, and they are not described.

According to this embodiment, as for driving of the hammer bit119, the impact driving structure is configured to be directly connected to the driving motor and only rotation is transmitted via the electromagnetic clutch134. Further, the electromagnetic clutch134is disposed on the output shaft111aof the driving motor111which is driven at high speed and low torque. With this construction, torque acting on the electromagnetic clutch134is reduced, so that the electromagnetic clutch134can be reduced in size and weight.

Further, according to this embodiment, with the construction in which the clutch shaft is coaxially disposed radially outward of the output shaft111a, the electromagnetic clutch134disposed on the output shaft111acan be reduced in size in its axial direction, so that rational space-saving arrangement can be realized. Further, in this embodiment, with the construction in which the electromagnetic clutch134is isolated from the gear housing space107asuch that the lubricant is avoided from adhering to it, like in the first embodiment, the electromagnetic clutch134has no risk of slippage by contact of its clutch face with the lubricant, so that a friction clutch having a high reaction rate can be used as the electromagnetic clutch134.

Further, this embodiment has the same effects as the above-described first embodiment. For example, when the hammer bit119is unintentionally locked during hammer drill operation, the electromagnetic clutch134is switched from the torque transmission state to the torque transmission interrupted state, so that the body103can be prevented from being swung by a reaction torque acting on the body103. Further, the electromagnetic clutch134provided for preventing excessive reaction torque from acting on the body103also serves as a clutch for switching between operation modes.

Further, in this embodiment, the magnetostrictive torque sensor151is used as a means for detecting reaction torque acting on the body103, but such means is not limited to this. For example, it may be constructed such that movement of the body103is measured by a speed sensor or an acceleration sensor and the reaction torque on the body103is detected from the measurements.

In view of the scope and spirit of the above-described invention, the following features can be provided.

“The impact tool as defined in claim1, wherein the path of transmitting torque of the motor to the tool bit includes an impact drive line for rectilinearly driving the tool bit in the axial direction and a rotation drive line for rotationally driving the tool bit around the axis, and the clutch is disposed in the rotation drive line.”

“The impact tool as defined in any one of claims1to10, comprising a non-contact torque sensor that detects torque acting on the tool bit during operation in non-contact with a rotating shaft that rotates together with the tool bit, wherein torque transmission by the clutch is interrupted when the torque value detected by the torque sensor exceeds a torque setting.”

“The impact tool as defined in (2), comprising a torque adjusting member that can be manually operated to adjust the torque setting which is set by the torque sensor.”

“The impact tool as defined in any one of claims1to10, comprising a speed sensor or an acceleration sensor that measures momentum of the tool body and detects reaction torque acting on the tool body from the measurement.”

“The impact tool as defined in any one of claim1to10or (1), wherein the clutch includes a driving-side clutch part and a driven-side clutch part, and one of the driving-side clutch part and the driven-side clutch part has a radially inner region and a radially outer region and comes into engagement with or disengagement from the other clutch part by displacement of the outer region with respect to the inner region.”

“The impact tool as defined in claim2, wherein the speed ratio between the motor output shaft and the clutch shaft is substantially the same.”

“The impact tool as defined in claim9, comprising a clutch housing space that houses the clutch isolated from the gear chamber, and a bearing which rotatably supports a shaft of the clutch and forms a sealing member that prevents the lubricant of the gear chamber from entering the clutch housing space.”

DESCRIPTION OF NUMERALS