Impact tool

It is an object of the invention to provide a technique which is effective in improving the durability of an angular positioning device of a tool bit and in reducing weight of a tool body in an impact tool. A representative impact tool includes a tool body, a lubricant sealed in the housing space, a driving mechanism, a tool holder, an angular positioning device disposed on a tip end side of the tool body and serves to fix a position of the tool bit around the axis with respect to the tool body. The angular positioning device includes first and second locking members. The first locking member is disposed between the tool body and the tool holder. The second locking member is disposed opposite to the first locking member. One end of the first locking member in the axial direction of the tool bit extends into the housing space of the tool body and is connected to the tool body within the housing space.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a technique of providing new and useful impact tool.

2. Description of the Related Art

An impact tool is provided with an angular positioning device which positions a hammer bit in its circumferential direction with respect to a tool body during hammering operation. For example, Japanese non-examined laid-open Patent publication No. 11-104974 discloses an impact tool having such an angular positioning device. The angular positioning device in the above publication is disposed in a tip end region of a barrel which forms a tool body. In the angular positioning device, a locking member is disposed between a barrel and a tool holder for holding the hammer bit. The locking member is normally connected via a spline fit with respect to the tool holder and can be connected to or disconnected from the barrel via engagement of projections and recesses. The position of the tool bit is adjusted by appropriately rotating the tool bit together with the tool holder in a state in which the locking member is disconnected from the barrel. Thereafter, the tool bit is fixedly positioned in the adjusted position by connecting the locking member to the barrel again.

In a construction in which the angular positioning device is disposed in the tip end region of the barrel, the angular positioning device is located close to the tool bit to be positioned. Therefore, the operability of the angular positioning device can be advantageously enhanced, but on the other hand, the angular positioning device is affected by dust of a workpiece (concrete) which is generated during hammering operation. Specifically, a connection between the locking member and the tool holder and a connection between the locking member and the barrel are caused to be susceptible to wear by entry of dust. Therefore, each of members of the angular positioning device including the barrel is formed from wear-resistant materials such as ferrous materials in order to enhance durability. Further, the impact tool which is held by the user's hand in hammering operation is desired to be as light as possible, and particularly as for the barrel having a relatively large volume, such is highly desired. However, if the barrel is formed from lighter materials than ferrous materials, such as nonferrous metals and synthetic resins, the required wear resistance cannot be ensured. In this point, further improvement is required.

On the other hand, Japanese non-examined laid-open Patent Publication No. 2000-127066 discloses an impact tool having an impact absorption mechanism for absorbing an impact during an idle driving movement. The known impact absorption mechanism is designed such that, when a tool bit is held away from a workpiece and a striker performs a striking movement, an elastic element is subjected to a load of an intermediate element which moves forward together with the striker, and thereby absorbs an impact caused by the striking movement of the striker. In other words, the impact absorption mechanism in the known impact tool is designed such that mainly one elastic element is subjected to an impact caused by the striker during idle driving. Therefore, the elastic element is subjected to a heavy load, so that further improvement is required in durability.

SUMMARY OF THE INVENTION

Accordingly, it is a first object of the invention to provide a technique which is effective in improving the durability of an angular positioning device of a tool bit and in reducing weight of a tool body in an impact tool.

Moreover, it is further a second object of the invention to provide a technique that contributes to improvement in durability of an impact absorption mechanism for absorbing impact during idle driving in an impact tool.

In order to achieve the above-described first object, in a preferred embodiment according to the invention, a representative impact tool which performs a predetermined hammering operation on a workpiece by a striking movement of a tool bit in an axial direction of the tool bit includes a tool body having a housing space, a lubricant sealed in the housing space and a driving mechanism which is housed within the housing space and drives the tool bit disposed in a tip end region of the tool body in the axial direction. Further, the “predetermined hammering operation” in this invention suitably includes not only a hammering operation in which the tool bit performs only a linear striking movement, but a hammer drill operation in which it performs a linear striking movement and a rotation in its circumferential direction.

According to the preferred embodiment of the impact tool according to the invention, the representative impact tool includes a tool holder which holds the tool bit in such a manner that the tool bit cannot rotate around an axis of the tool bit with respect to the tool holder and which is disposed in the tool body in such a manner that it can rotate around the axis of the tool bit, and an angular positioning device which is disposed on a tip end side of the tool body and serves to fix a position of the tool bit around the axis with respect to the tool body. The angular positioning device has first and second locking members. The first locking member is disposed between the tool body and the tool holder in a direction transverse to the axial direction of the tool bit, and connected to the tool body in such a manner that the first locking member cannot rotate around the axis of the tool bit with respect to the tool body and can rotate around the axis of the tool bit with respect to the tool holder. The second locking member is disposed opposite to the first locking member and connected to the tool holder in such a manner that it cannot rotate around the axis of the tool bit while being allowed to move in the axial direction of the tool bit with respect to the tool holder. Further, the second locking member can be connected to or disconnected from the first locking member according to the movement of the second locking member in the axial direction of the tool bit, in such a manner that it cannot rotate around the axis of the tool bit with respect to the first locking member. One end of the first locking member in the axial direction of the tool bit extends into the housing space of the tool body and is connected to the tool body within the housing space. The “first and second locking members” in this invention are typically formed by a cylindrical member, but suitably include those formed by a semi-cylindrical member.

The angular positioning device in the invention is disposed in the tip end region of the tool body. This position is located close to the tool bit to be positioned, so that the angular positioning device can achieve higher operability. On the other hand, the angular positioning device is exposed to dust which is generated during hammering operation and caused to be susceptible to wear. Therefore, in the invention, connection between the first locking member and the tool body is made in the housing space of the tool body or in oil. Thus, the connection between the first locking member and the tool body can be avoided from being adversely affected by dust during hammering operation and protected by the lubricant sealed in the housing space. Therefore, as for the tool body which occupies a much larger volume compared with the first and second locking members, while its wear problem is solved, it is formed from nonferrous metals such as an aluminum alloy and a synthetic resin which are lighter in weight than ferrous materials, so that the weight of the impact tool can be reduced. Further, the first locking member and the second locking member are formed from wear-resistant ferrous materials, so that their durability can be enhanced.

According to a further embodiment of the impact tool of the invention, a third locking member is disposed between the first locking member and the second locking member in the axial direction of the tool bit. The third locking member is normally connected to the first locking member and can be connected to or disconnected from the second locking member according to the movement of the second locking member in the axial direction of the tool bit. Further, one surface of the third locking member in a direction transverse to the axial direction of the tool bit contacts the tool body and the other surface contacts a surface of the tool holder which extends in a direction transverse to the axial direction, so that the third locking member serves as a stopper for preventing the tool holder from moving toward the housing space. Specifically, in the invention, the tool holder contacts the end surface of the tool body on the tip end side in the axial direction of the tool bit via the third locking member, so that the tool holder is prevented from moving to the housing space side.

When the tool holder is mounted within the tool body, for example, by inserting the tool holder from the housing space side of the tool body toward the tip end side, the inserted tool holder needs to be prevented from becoming detached from the tool body. According to the invention, the stopper ring is fitted onto the inserted tool holder. The stopper ring contacts the third locking member which is held in contact with the tool body and thus locked against movement in a direction in which it may become detached. As a result, the tool holder is locked against movement in a direction in which it may become detached. Specifically, according to the invention, the third locking member can be provided with not only a primary function of positioning but a function as a stopper for the tool holder, so that a rational construction for preventing the tool holder from becoming detached can be realized.

According to a further embodiment of the impact tool of the invention, the second locking member and the third locking member have projections and recesses, respectively, in regions opposite to each other in the axial direction of the tool bit and are connected to each other by engagement of the projections and recesses. With such construction, the second locking member can be smoothly connected to or disconnected from the third locking member by moving the second locking member in the axial direction of the tool bit.

According to a further embodiment of the impact tool of the invention, the angular positioning device has an operating member which is operated to move the second locking member in the axial direction of the tool bit, and one end of the operating member is connected to the second locking member and the other end is exposed on the tool body such that the operating member can be manually operated by a user. According to this invention, the second locking member can be easily operated from outside the tool body.

According to a further embodiment of the impact tool of the invention, a tool holder guide made of a ferrous material is radially disposed between the tool body and the tool holder in a direction transverse to the axial direction of the tool bit and the tool holder guide forms the first locking member. With such construction, the tool holder guide or the first locking member can be made of a ferrous material, so that durability can be enhanced.

In order to achieve the above-described second object, in a preferred embodiment according to the invention, a representative impact tool which performs a predetermined hammering operation on a workpiece by a striking movement of a tool bit in an axial direction of the tool bit includes a striker, an intermediate element, a first receiving portion, a second receiving portion, a first elastic element and a second elastic element. Further, the “predetermined hammering operation” in this invention suitably includes not only a hammering operation in which the tool bit performs only a striking movement in its axial direction, but a hammer drill operation in which it performs a linear striking movement and a rotation in its circumferential direction. The striker linearly moves forward in order to strike the tool bit. The intermediate element transmits a striking force of the striker to the tool bit. The first receiving portion contacts the striker when the striker further moves forward beyond a predetermined striking position in order to strike the intermediate element. The second receiving portion contacts the intermediate element when the striker moves forward beyond the striking position and strikes and moves the intermediate element forward. The first elastic element is held in contact with the first receiving portion and elastically deforms by an impact which is caused by contact of the striker with the first receiving portion and transmitted to the first elastic element. The second elastic element is prevented from moving forward by the tool body or by a member on the tool body side which is prevented from moving forward by the tool body. Further, the second elastic element is held in contact with the first and second receiving portions and elastically deforms by an impact which is caused by contact of the striker with the first receiving portion and transmitted from the first receiving portion, and by an impact which is caused by contact of the intermediate element with the second receiving portion and transmitted from the second receiving portion.

According to the preferred embodiment of the invention, the first and second receiving portions are disposed side by side in contact with the second elastic element. Further, the manner of being “disposed side by side in contact” with the second elastic element in this invention suitably includes the manner of being disposed side by side in the radial direction of the tool bit and held in contact with the second elastic element and the manner of being disposed side by side in the circumferential direction of the tool bit and held in contact with the second elastic element. According to the invention, the first and second elastic elements can share and absorb an impact caused by the idle driving movement of the striker, so that the durability of the elastic elements can be improved. Further, in this invention, with the construction in which the first receiving portion and the second receiving portion are disposed side by side in contact with the second elastic element, an impact on the side of the striker can be effectively transmitted to the second elastic element, regardless of timing of contact of the striker with the first receiving portion and contact of the intermediate element with the second receiving portion. The “first and second elastic elements” in this invention typically comprise rubber. Further, the “first and second elastic elements” suitably include both of those which are continuously formed around the axis (in the circumferential direction) of the tool bit and those which are discontinuously formed around the axis of the tool bit.

According to a further embodiment of the invention, one of the first and second receiving portions is held in contact with a radially outward portion of the second elastic element and the other receiving portion is held in contact with a radially inward portion of the second elastic element. With such construction, impact transmission from the first and second receiving portions to the second elastic element can be realized in a rational arrangement.

According to a further embodiment of the invention, the first receiving portion comprises a stepped member having a protrusion extending forward from its radially outer edge and is held in contact with the radially outward portion of the second elastic element via the protrusion. The “protrusion” in this invention typically comprises the protrusion which is continuously formed in the circumferential direction of the tool bit, but it also suitably includes the protrusion which is discontinuously formed in the circumferential direction of the tool bit. In this invention, with the above-described construction, the first receiving portion can transmit an impact to the radially outward portion of the second elastic element via its protrusion, while avoiding interference with the second receiving portion which is held in contact with the radially inward portion of the second elastic element. Further, when the second receiving portion is formed, for example, by the tool holder for holding the tool bit, interference with the tool holder can be avoided. Therefore, even if the first and second elastic elements are installed under a pre-load, the tool holder has no resistance. Therefore, this construction does not affect the operability in rotating the tool holder in the circumferential direction together with the tool bit in order to position the tool bit in its circumferential direction.

According to a further embodiment of the invention, the stepped member having the protrusion is disposed on the front and rear sides of the first elastic element. The front and rear stepped members have the same shape and are disposed in symmetry on the both sides of the first elastic element. With such construction, the front and rear stepped members can be common parts. Therefore, proper installation of the front and rear stepped sleeves is ensured, so that ease of assembly can be improved.

Some impact tools have an idle driving prevention mechanism of such a type that prevents the striker from repeating idle driving movement by holding the striker in the forward position when the striker is further moved forward beyond the striking position. Such an idle driving prevention mechanism includes a front bore space which is provided to prevent the idle driving movement and defined in the forward portion of the cylinder in which the striker is slidably housed, an air vent that provides communication between the outside and the inside of the front bore space, and a non-return valve that normally closes the air vent, while being pushed outward by the air escaping through the air vent when the striker moves further forward beyond the striking position within the front bore space. When the striker that slides within the cylinder moves further forward beyond the predetermined striking position of the intermediate element, air within the front bore space is compressed by the striker and pushes the non-return valve (O-ring) outward so that the air escapes to the outside through the air vent formed in the cylinder. Thereafter, when the striker tries to move back to its pre-striking position, a negative pressure is caused in the front bore space because the non-return valve prevents inflow of outside air. As a result, the striker is prevented from moving back and held in a position forward of the striking position. Thus, the striker is prevented from repeating idle driving movement. In such an idle driving prevention mechanism using a non-return valve, when the non-return valve is pushed outward by the air escaping through the air vent, the non-return valve may be displaced in the axial direction of the tool bit.

According to the invention, when this invention is applied to an impact tool having an idle driving prevention mechanism as described above, the protrusion of the rear stepped member can be disposed opposite to a side of the non-return valve in its axial direction. Therefore, when the non-return valve is pushed outward, the protrusion can prevent the non-return valve from being displaced in its axial direction, so that any problem which may be caused by displacement of the non-return valve can be avoided.

According to a further embodiment of the invention, the impact tool further includes a cylinder that houses the striker and has a rear end surface and a front end surface in the axial direction of the tool bit which are held in contact with the tool body and the first receiving portion, respectively. Further, the first and second elastic elements are installed under a predetermined pre-load, so that the cylinder is held in the axial direction of the tool bit. According to the invention, the cylinder can be held by the elastic forces of the first and second elastic elements, so that a member for holding the cylinder (O-ring) can be omitted. Further, rattling of the cylinder is suppressed, so that vibration in the impact tool can be lowered.

DETAILED DESCRIPTION OF THE INVENTION

First Representative Embodiment

An embodiment of the invention is now described with reference toFIGS. 1 to 5. In this embodiment, an electric hammer is explained as a representative example of an impact tool according to the invention.FIG. 1shows an entire structure of an electric hammer101.FIG. 2is an enlarged view showing the structure of an essential part of the electric hammer101.FIGS. 3 to 5are enlarged views showing the structure of an angular positioning device for positioning a hammer bit in its circumferential direction with respect to a tool body.FIG. 3shows a rotation prevented state or positioned state of a tool holder, andFIG. 4shows a rotation allowed state of the tool holder.FIG. 5is a sectional view of the angular positioning device along a different line from the sectional views ofFIGS. 3 and 4.

As shown inFIG. 1, the electric hammer101according to this embodiment includes a body103that forms an outer shell of the electric hammer101, a tool holder137that is connected to a tip end region (on the left side as viewed inFIG. 1) of the body103in its longitudinal direction, a hammer bit119detachably coupled to the tool holder137, and a handgrip109that is connected to the other end of the body103in its longitudinal direction (on the right side as viewed inFIG. 1) and designed to be held by a user. The body103and the hammer bit119are features that correspond to the “tool body” and the “tool bit”, respectively, according to the invention. The hammer bit119is held by the tool holder137such that it is allowed to reciprocate with respect to the tool holder137in its axial direction (the longitudinal direction of the body103) and prevented from rotating with respect to the tool holder137in its circumferential direction. For the sake of convenience of explanation, the side of the hammer bit119is taken as the front side and the side of the handgrip109as the rear side.

The body103mainly includes a motor housing105that houses a driving motor111, a crank housing107that houses a motion converting mechanism113, and a generally cylindrical barrel108that houses a striking mechanism115. The motion converting mechanism113is adapted to appropriately convert the rotating output of the driving motor111to linear motion and then to transmit it to the striking mechanism115. As a result, an impact force is generated in the axial direction of the hammer bit119via the striking mechanism115. The barrel108in the form of a cylindrical housing is connected to the front end of the crank housing107and extends forward in the axial direction of the hammer bit119. Further, the handgrip109is generally U-shaped having an open front and connected to the rear of the motor housing105. A power switch131and an actuating member133are disposed in the upper region of the handgrip109. The power switch131electrically drives the driving motor111, and the actuating member113is slid by a user to actuate the power switch113between on and off positions.

The rotating output of the driving motor111is appropriately converted into linear motion via the motion converting mechanism113and transmitted to the striking mechanism115. As a result, an impact force is generated in the axial direction of the hammer bit119via the striking mechanism115. The driving motor111is arranged such that the axis of a motor shaft112crosses the axis of the hammer bit119. The motion converting mechanism113and the striking mechanism115are features that correspond to the “driving mechanism” according to the invention.

The motion converting mechanism113serves to convert rotation of the driving motor111into linear motion and transmit it to the striking mechanism115. The motion converting mechanism113is formed by a crank mechanism which includes a crank shaft121that is rotationally driven via a plurality of gears by the driving motor111, a crank arm123that is connected to the crank shaft121via an eccentric pin at a position displaced from the center of rotation of the crank shaft121and a piston125that is caused to reciprocate via the crank arm123. The piston125forms a driving element that drives the striking mechanism115and can slide within a cylinder141in the axial direction of the hammer bit119. The crank mechanism is housed within a crank chamber116which is an enclosed housing space in a crank housing107. A lubricant (grease) is sealed in the crank housing107.

The striking mechanism115mainly includes a striking element in the form of a striker143that is slidably disposed within the bore of the cylinder141, and an intermediate element in the form of an impact bolt145that is slidably disposed in the tool holder137and transmits the kinetic energy of the striker143to the hammer bit119. An air chamber141ais defined between the piston125and the striker143within the cylinder141. The striker143is driven via the action of an air spring of the air chamber141a of the cylinder141which is caused by sliding movement of the piston125. The striker143then collides with (strikes) the intermediate element in the form of the impact bolt145that is slidably disposed within the tool holder137, and transmits the striking force to the hammer bit119via the impact bolt145.

In the electric hammer101having the above-described construction, when the driving motor111is driven under loaded conditions in which the hammer bit119is pressed against the workpiece by the user's pressing force applied forward to the tool body103(as viewed inFIGS. 1 and 2), the piston125is caused to linearly slide along the cylinder141via the motion converting mechanism113that mainly comprises the crank mechanism. When the piston125slides, the striker143moves forward within the cylinder141by the action of the air spring of the air chamber141aof the cylinder141and collides with the impact bolt145. The kinetic energy of the striker143which is caused by the collision with the impact bolt145is transmitted to the hammer bit119. Thus, the hammer bit119performs the hammering operation on a workpiece (concrete).

The tool holder137is provided such that it is allowed to rotate around the axis of the hammer bit with respect to the barrel108. The hammer bit119is inserted into a bit holding hole138of the tool holder137from the front of the tool holder137and held by a bit holding device136disposed in the tip end region of the tool holder137. The bit holding device136has an engagement member in the form of a plurality of engagement pawls136aformed in the circumferential direction, and holds the hammer bit119via the engagement pawls136asuch that the hammer bit is prevented from being pulled out. The hammer bit119has axially extending grooves formed in its outer surface, and the grooves engage with a plurality of lugs138aformed on an inner circumferential surface of the bit holding hole138and extending radially inward. Thus, the hammer bit119is prevented from rotating in the circumferential direction with respect to the tool holder137. Specifically, the hammer bit119is held such that it is prevented from becoming detached from the tool holder137and also prevented from rotating in the circumferential direction with respect to the tool holder137. The bit holding device136does not particularly relate to the invention, and thus explanation of its specific structure is omitted.

Next, an angular positioning device181is described with reference toFIGS. 2 to 5, which serves to fix the angular position of the hammer bit119held by the tool holder137, around the axis or in the circumferential direction of the hammer bit119. The angular positioning device181is disposed in a tip end region (on the front end side) of the barrel108, and mainly includes a tool holder guide183in the form of a generally cylindrical member, a generally annular locking ring185for securing the positioning and a generally cup-like changing ring187. The tool holder guide183holds the tool holder137in such a manner that the tool holder137can rotate around the axis of the hammer bit, and the tool holder guide183is normally connected to the barrel108in such a manner that it cannot rotate with respect to the barrel108. The locking ring185for securing the positioning is normally connected to the tool holder guide183in such a manner that it cannot rotate with respect to the tool holder guide183. The changing ring187prevents the tool holder137from rotating when the changing ring187is connected to the locking ring185, while it allows the tool holder137to rotate when it is disconnected from the locking ring185. The tool holder guide183, the changing ring187and the locking ring187are features that correspond to the “first locking member”, the “second locking member” and the “third locking member”, respectively, according to the invention.

The barrel108is made of nonferrous metals such as an aluminum alloy and a synthetic resin in order to realize weight reduction, and has a circular tool holder holding hole108bhaving a predetermined length in the axial direction of the hammer bit on the tip end side of the barrel108. The tool holder guide183is a cylindrical member made of iron and fitted into the tool holder holding hole108bof the barrel108from the rear (from the right as viewed in the drawings). Then, the tool holder137is inserted into the bore of the tool holder guide183from the rear. Specifically, the tool holder guide183is disposed between the tool holder137and the barrel108. The tool holder guide183has a flange183aextending radially outward from the axial rear end of the tool holder guide183, and a plurality of pawls183bformed on the front of the flange183aat predetermined intervals in the circumferential direction. The pawls183bof the tool holder guide183engage with a plurality of grooves108cwhich are formed in the circumferential direction in the inner wall surface of the barrel on the rear end side of the tool holder holding holes108band designed and arranged to correspond to the pawls183b. Thus, the tool holder guide183is normally held connected to the barrel108in such a manner as to be prevented from moving in the circumferential direction with respect to the barrel108.

An inner space108dis defined in the rear of the tool holder holding hole108bof the barrel108and houses the cylinder141and an impact absorption mechanism135for absorbing an impact during an idle driving movement of the striker143. Further, the inner space108dis filled with lubricating oil. Therefore, the tool holder guide183is connected to the barrel108in lubricating oil within the inner space108d. The inner space108dis a feature that corresponds to the “housing space” according to the invention. An O-ring184is disposed between the mating surfaces of the tool holder137and the tool holder guide183, so that the lubricating oil is prevented from leaking out of the inner space108dthrough a clearance between the mating surfaces.

The tool holder137is made of iron and has a flange137aextending radially outward from the axial rear end of the tool holder137. Further, a rubber ring163and a flat washer165of the impact absorption mechanism135are disposed between the flange137aof the tool holder137and the flange183aof the tool holder guide183. Specifically, the flange183aof the tool holder guide183is held between the rubber ring163and an engagement surface108awhich is formed in the barrel108in a direction transverse to the axial direction, so that it is locked against axial movement. As a result, the tool holder guide183is held connected to the barrel108. The impact absorption mechanism135does not particularly relate to the invention, and thus explanation of its specific structure is omitted.

The axial front end183cof the tool holder guide183protrudes a predetermined extent forward from the front end of the barrel108, and a plurality of grooves183d(seeFIG. 5) are formed in the protruding front end183cat appropriate intervals in the circumferential direction. The iron locking ring185is fitted on the front end183cof the tool holder guide183. A plurality of radially extending pawls185aare formed on the inner circumferential surface of the locking ring185in the circumferential direction and designed and arranged to correspond to the grooves183dof the front end183c. The pawls185aengage with the grooves183dof the front end183c(seeFIG. 5). Thus, the tool holder guide183is normally connected to the locking ring185in such a manner that it cannot move in the circumferential direction. Further, a plurality of positioning grooves (recesses)185bare formed in the outer circumferential surface of the locking ring185at equal intervals in the circumferential direction (seeFIG. 4).

A stopper ring197is fitted on the tool holder137at a position adjacent to the front end of the tool holder guide183and disposed opposite to a front end surface of a radially inward portion of each of the pawls185aof the locking ring185in such a manner that it can contact this front end surface (seeFIG. 5). Further, the locking ring185is held in contact with the front end surface108eextending in a direction transverse to the axial direction of the barrel108. Therefore, the locking ring185serves as a stopper for preventing the tool holder137from moving rearward (to the inner space108dside of the barrel108) when the tool holder137is mounted to the barrel108.

The changing ring187is made of iron and mounted on the tool holder137in front of the locking ring185. The changing ring187is mounted onto the tool holder137via a spline fit186between a front small-diameter portion of the changing ring187and the tool holder137, so that the changing ring187can move in the axial direction and cannot rotate in the circumferential direction with respect to the tool holder137. A plurality of positioning pawls187aare formed on a rear end surface of the changing ring187which is opposed to the locking ring185, at equal intervals in the circumferential direction, and designed and arranged to correspond to the positioning grooves185bof the locking ring185. When the changing ring187is moved rearward toward the locking ring185, the pawls187aof the changing ring187engage with the positioning grooves185bof the locking ring185. Thus, the changing ring187is connected to the locking ring185in such a manner that it cannot move in the circumferential direction with respect to the locking ring185. As a result, the changing ring187as well as the tool holder137is prevented from rotating. On the other hand, when the changing ring187is moved forward away from the locking ring185, the pawls187aare disengaged from the grooves185bof the locking ring185and the changing ring187as well as the tool holder137is allowed to rotate. The positioning grooves185band the positioning pawls187aare features that correspond to the “projections and recesses” according to the invention.

Specifically, the changing ring187can be moved in the axial direction between a rotation prevented position in which the tool holder137is prevented from rotating by engagement of the pawls187awith the grooves185bof the locking ring185and a rotation allowed position in which the tool holder137is allowed to rotate by disengagement of the pawls187afrom the grooves185bof the locking ring185. Further, the changing ring187is biased to the rotation prevented position by a biasing member in the form of a coil spring189and holds the tool holder137in the rotation prevented state unless acted upon by an external force for moving the changing ring187to the rotation allowed position.

An operating member in the form of an operating sleeve191is coupled to the changing ring187and operated to move the changing ring187between the rotation prevented position and the rotation allowed position. A front end of the operating sleeve191is mounted on the changing ring187via a stopper ring193, so that the operating sleeve191is prevented from moving in the axial direction and rotating in the circumferential direction with respect to the changing ring187. Specifically, the operating sleeve191is integrated with the changing ring187and its rear end side is exposed on a barrel cover106for covering the barrel108so that the operating sleeve191can be operated by the user from outside. Further, the coil spring189is disposed between the front end surface of the operating sleeve191and a spring receiver195which is disposed within the above-described bit holding device136in the tip end region of the tool holder137, and applies a biasing force to the operating sleeve191and the changing ring187toward the rotation prevented position.

Operation of the angular positioning device181having the above-described construction according to this embodiment is now explained. In order to fix the circumferential position of the hammer bit119with respect to the barrel108, the user moves the operating sleeve191forward by hand against the biasing force of the coil spring189and moves the changing ring187to the rotation allowed position. Thus, the pawls187aof the changing ring187are disengaged from the grooves185bof the locking ring185, so that the tool holder137is allowed to rotate with respect to the barrel108(the tool holder guide183) or released from the fixedly positioned state. Next, when the user turns the operating sleeve191in the circumferential direction in this released state, the tool holder137is rotated together with the changing ring187integrated with the operating sleeve191, which in turn causes the hammer bit119and the bit holding device136to rotate together with the tool holder137. In this manner, the circumferential position of the hammer bit119with respect to the barrel108is fixed. Thereafter, when the changing ring187is moved to the rear rotation prevented position together with the operating sleeve191, the pawls187aengage with the grooves185bof the locking ring185again. Thus, the hammer bit119, the bit holding device136and the tool holder137are prevented from rotating in the circumferential direction with respect to the barrel108and locked in the fixed angular position.

With the angular positioning device181according to this embodiment, the user can perform the angular positioning of the hammer bit119in its circumferential direction by operating the operating sleeve191by one hand, while, for example, holding the barrel108by the other hand, so that positioning of the hammer bit119can be performed without impairing the operability of the known angular positioning device.

The angular positioning device181according to this embodiment is disposed in the tip end region of the barrel108. The tip end region of the barrel108is located in the vicinity of the hammer bit119to be positioned, so that the user can operate the operating sleeve191in the vicinity of the hammer bit119. Therefore, the angular positioning device181having higher operability is provided. On the other hand, the angular positioning device181disposed in the tip end region of the barrel108is exposed to dust which is generated during hammering operation. As a result, a connection which is formed by a sliding part in the angular positioning device181is caused to be susceptible to wear under the influence of dust. If all of the members of the angular positioning device which have a connection are formed of wear-resistant materials such as iron in order to overcome this problem of wear, the electric hammer101will increase in weight.

In this embodiment, the tool holder guide183is disposed between the tool holder137and the barrel108in such a manner that it extends into the inner space108dof the barrel108and is connected to the barrel108in oil within the inner space108d. With such construction, this connection can be avoided from being adversely affected by dust and can be protected by the lubricant. Therefore, the barrel108which has a relatively large volume among the component parts relating to the angular positioning device181is formed from nonferrous materials such as an aluminum alloy, in order to reduce the weight of the electric hammer101while reducing wear. The tool holder guide183, the locking ring185and the changing ring187are formed from wear-resistant materials such as ferrous materials, so that their durability can be enhanced.

In assembly of the electric hammer101, at least the tool holder guide183, the tool holder137, the locking ring185, the rubber ring163and the flat washer165are mounted to the barrel108prior to mounting of the barrel108to the crank housing107. This mounting operation is performed, for example, in the following procedure. Firstly, the tool holder guide183is inserted into the tool holder holding holes108bof the barrel108from the rear, and then the tool holder137on which the flat washer165and the rubber ring163are mounted in advance is inserted into the bore of the tool holder guide183from the rear. Subsequently, the locking ring185is fitted onto the outer periphery of the front end183aof the tool holder guide183, and finally, the stopper ring197is fitted onto the tool holder137. The stopper ring197is held in contact with the front end surface of the radially inward portion of each of the pawls185aof the locking ring185, so that the tool holder137mounted to the barrel108in the above-described manner is prevented from becoming dislodged. Specifically, according to this embodiment, the locking ring185can be provided with a function as a stopper for preventing the tool holder137from becoming dislodged, as well as a function for positioning the tool holder137in its circumferential direction. Thus, a plurality of component parts are mounted to the barrel108in advance in order to form an assembly, and in this assembled state, the barrel108can be mounted to the crank housing107, so that ease of assembly can be enhanced.

Further, in this embodiment, the locking ring185is disposed between the tool holder guide183and the changing ring187, but it may be altered such that the changing ring187is directly connected to and disconnected from the tool holder guide183without providing the locking ring185. Further, in this embodiment, the electric hammer101is described as an example of a representative impact tool in which the hammer bit119performs only a striking movement in the axial direction. However, the invention can also be applied to a hammer drill in which the hammer bit119performs a striking movement in the axial direction and a rotation in the circumferential direction, for example, by additionally providing the angular positioning device181with a means for locking the changing ring187in a rotation allowed position in which the tool holder137is allowed to rotate.

Second Representative Embodiment

Second representative embodiment of the invention is now described with reference toFIGS. 6 to 9. In this embodiment, an electric hammer is explained as a representative example of an impact tool according to the invention.FIG. 6shows an entire structure of an electric hammer101.FIGS. 7 and 8show the structure of an essential part of the electric hammer according to the invention.FIG. 9is a partially enlarged view ofFIG. 8. The electric hammer according to the second representative embodiment has substantially the same construction with the electric hammer. In this connection, detailed explanation of same features with the first representative embodiment is abbreviated.

When the user stops applying the pressing force against the workpiece to the hammer bit119in order to finish the hammering operation, the striker143performs an idle driving movement, or the striking movement under unloaded conditions in which no load is applied to the hammer bit119. During this idle driving movement, the striker143collides with the impact bolt145under loaded conditions. In other words, the striker143moves further forward beyond a striking position at which the striker strikes the impact bolt. In order to absorb the impact caused by the idle driving movement of the striker143, an impact absorption mechanism135is provided within the barrel108on the front end side. The impact absorption mechanism135mainly includes a rear cushioning member151and a front cushioning member161which are disposed side by side in the axial direction of the hammer bit119.

FIGS. 7 to 9show the impact absorption mechanism135. As shown inFIGS. 7 to 9, the rear cushioning member151mainly includes an elastically deformable first rubber ring153and metallic front and rear stepped sleeves155,157between which the first rubber ring153is held. The rear cushioning member151is disposed on the rear small-diameter portion145bof the impact bolt145. The first rubber ring153and the front and rear stepped sleeves155,157are features that correspond to the “first elastic element” and the “first receiving portion”, respectively, according to this invention. Annular portions155a,157aare formed on radially outer edges of the front and rear stepped sleeves155,157, respectively, and extend in the axial direction of the hammer bit such that the stepped sleeves155,157are symmetrically formed. Specifically, the annular portion155aof the front stepped sleeve155extends forward and the annular portion157aof the rear stepped sleeve157extends rearward. The annular portions155a,157aare features that correspond to the “protrusion” according to this invention. The rear stepped sleeve157is arranged such that its rear surface is held in contact with the front end surface of the cylinder141and the annular portion157ais fitted over the cylinder141. The front stepped sleeve155is arranged such that it is held in contact with a radially outward portion of a rear surface of a flat washer165of the front cushioning member161which is described below in detail.

The front cushioning member161mainly includes an elastically deformable second rubber ring163, a metallic flat washer165disposed at the rear of the second rubber ring163, and a tool holder137. The second rubber ring163and the flat washer165are disposed on a rear end portion of the generally cylindrical tool holder137. The second rubber ring163and the tool holder137are features that correspond to the “second elastic element” and the “second receiving portion”, respectively, according to this invention. A generally cylindrical tool holder guide139is disposed between the outer surface of the tool holder137and the inner surface of the barrel108, and the second rubber ring163is held in contact with a rear end surface of the tool holder guide139. The tool holder guide139has a flange139aextending radially outward from its axial rear end, and the flange139ais held in contact with a radial engagement surface108aformed in the inner wall of the barrel108. Thus, the tool holder guide139is prevented from moving forward with respect to the barrel108. The tool holder guide139is a feature that corresponds to the “member on the tool body side” according to this invention. The tool holder137has a flange137aextending radially outward from the axial rear end of the tool holder137, and the flange137ais held in contact with a radially inward portion of the rear surface of the flat washer165.

Specifically, the annular portion155aof the front stepped sleeve155of the rear cushioning member151and the flange137aof the tool holder137of the front cushioning member161are disposed side by side in contact with the radially outward and inward portions of the rear surface of the flat washer165, respectively. Therefore, an impact on the striker143side and an impact on the impact bolt145side which are caused during the idle driving movement of the striker143are transmitted (inputted) to the flat washer165in parallel. Further, the thickness (longitudinal extent) of the flange137ais designed to be smaller than the protruding extent of the annular portion155aof the front stepped sleeve155, so that a predetermined clearance C is defined between a rear surface of the flange137aand a front surface of the front stepped sleeve155which are opposed to each other.

In the impact absorption mechanism135having the above-described construction according to this embodiment, the second rubber ring163, the flat washer165, the flange137aof the tool guide137, the front stepped sleeve155, the first rubber ring153and the rear stepped sleeve157are arranged in series in the axial direction of the hammer bit in this order from the tool holder guide139side or from the front between the rear surface of the flange139aof the tool holder guide139and the front end surface of the cylinder141. Further, the impact absorption mechanism135is installed with the first and second rubber rings153,163preloaded in the axial direction of the hammer bit.

The impact bolt145has a stepped, columnar form having a large-diameter portion145athat is slidably held by the tool holder137, a front small-diameter portion145cformed at the front of the large-diameter portion145a,a rear small-diameter portion145bformed at the rear of the large-diameter portion145a,and a front tapered surface145dbetween the large-diameter portion145aand the front small-diameter portion145c. The impact bolt145is prevented from moving further forward by contact of the front tapered surface145dwith a stopper in the form of an inner wall tapered surface137bof the tool holder137. The rear small-diameter portion145bof the impact bolt145protrudes rearward from the rear end of the tool holder137and faces a front bore space173of the cylinder141. The rear end surface of the rear small-diameter portion145bof the impact bolt145is retracted from the rear surface of the rear stepped sleeve157into the bore or moved away from the front end surface (striking face) of the striker143when the impact bolt145is moved to a forward end position (a position in which the front tapered surface145dcomes into contact with the inner wall tapered surface137bof the tool holder137).

In the impact absorption mechanism135having the above-described construction according to this embodiment, when an idle driving movement of the striker143is performed under the unloaded conditions in which the user stops pressing the hammer bit119against the workpiece in order to finish the hammering operation, the striker143moves further forward beyond a proper striking position. When the striker143moves forward beyond the striking position and comes into contact with the rear surface of the rear stepped sleeve157, as shown inFIGS. 8 and 9, the kinetic energy of the striker143is transmitted to the barrel108via the rear stepped sleeve157, the first rubber ring153, the front stepped sleeve155, the annular portion155aof the front stepped sleeve155, the flat washer165, the second rubber ring163and the tool holder guide139. In this process, the kinetic energy is absorbed by elastic deformation of the first rubber ring153and the second rubber ring163in the transmission path. Specifically, the impact caused by contact of the striker143with the rear surface of the rear stepped sleeve157is absorbed by elastic deformation of the first rubber ring153and the second rubber ring163.

Further, when the striker143applies a striking force to the impact bolt145during further forward movement beyond the striking position, the impact bolt145moves forward and the front tapered surface145dcontacts the inner wall tapered surface137bof the tool holder137. Therefore, the kinetic energy of the impact bolt145is transmitted to the barrel108via the flange137aof the tool holder137, the flat washer165, the second rubber ring163and the tool holder guide139and absorbed by elastic deformation of the second rubber ring163in this transmission path. Specifically, the impact caused by contact of the impact bolt145with the tool holder137is absorbed by elastic deformation of the second rubber ring163.

Thus, in the impact absorption mechanism135according to this embodiment, the impact caused by the idle driving movement of the striker143is absorbed by the first rubber ring153and the second rubber ring163, so that the impact can be prevented from being transmitted to the barrel108.

According to this embodiment, the impact caused by contact of the striker143with the rear stepped sleeve157is received not only by the first rubber ring153, but also by the second rubber ring163which serves to receive an impact from the impact bolt145. Specifically, the first rubber ring153and the second rubber ring163can share the impact. Therefore, the load applied on the first rubber ring153and the second rubber ring163can be alleviated, so that their durability can be improved. Particularly, in this embodiment, impacts from the striker143and the impact bolt145are transmitted to the second rubber ring163in parallel. With this construction, the impact on the striker143side can be effectively transmitted to the second rubber ring163, regardless of timing of contact of the striker143with the rear stepped sleeve157and contact of the impact bolt145with the tool holder137.

Further, in the electric hammer101according to this embodiment, an idle driving prevention mechanism171for preventing the striker143from repeating idle driving movement is provided in a front end region (tip end region) of the cylinder141. When the striker143moves further forward beyond the striking position at which the striker143strikes the hammer bit119, under unloaded conditions in which the hammer bit119is not pressed against the workpiece, the idle driving prevention mechanism171prevents the striker143from moving back to a pre-striking position (a position at which the striker143is placed before striking), so that the striker143can be prevented from repeating idle driving movement. The idle driving prevention mechanism171mainly includes the front bore space173of the cylinder141, a plurality of air vents175which provide communication between the inside and the outside of the front bore space173, and an elastically deformable O-ring177which serves as a non-return valve for opening and closing the air vents175.

The front bore space173is defined as a space which is enclosed by the bore inner wall surface of the cylinder141, the front surface of the striker143, the rear surface of the impact bolt145and the rear surface of the rear stepped sleeve157. A plurality of the air vents175are formed radially through the cylinder141and arranged on the same circumference. The air vents175are normally closed by the O-ring177fitted on the outer circumferential surface of the cylinder141. An opening178is formed in the cylinder141rearward of the air vents175and has a larger cross-sectional area than the air vents175. The opening178is formed at a position in which it is closed by the periphery of the striker143when the striker143moves forward beyond the striking position.

When the striker143moves forward beyond the striking position and closes the opening178, air within the front bore space173is compressed by the further forward movement of the striker143and then escapes to the outside through the air vents175while pushing the O-ring177outward. Thereafter, when the striker143tries to move back to the pre-striking position by suction force of the air chamber141a of the cylinder141, a negative pressure is caused in the front bore space173because the O-ring177prevents inflow of outside air. As a result, the striker143is prevented from moving back and held in a position forward of the striking position. Thus, the striker143is prevented from repeating idle driving movement.

In this embodiment, the annular portion157aof the rear stepped sleeve157is disposed opposite to the front of the O-ring177. Therefore, when the air within the front bore space173escapes to the outside through the air vents175, the annular portion157aprevents the O-ring177from moving forward in the axial direction. Thus, the O-ring177can be prevented from being displaced forward in the axial direction. Further, in order to prevent the O-ring177from being displaced rearward in the axial direction, an O-ring guide179is provided on the cylinder141rearward of the O-ring177and prevents the O-ring177from moving reward. As a result, return of the O-ring177to its initial position (closing position) is ensured.

Further, in this embodiment, the first rubber ring153and the second rubber ring163are mounted under a predetermined pre-load (in a pressed state). Therefore, the cylinder141can be held pressed against the radial engagement surface107bof the bore107aof the crank housing107by the elastic forces of the first rubber ring153and the second rubber ring163. Therefore, a securing member (O-ring) for securing the cylinder141within the bore107aof the crank housing107can be omitted. Further, rattling of the cylinder141can be suppressed, so that vibration of the electric hammer101can be lowered.

Further, as described above, by the elastic forces of the first rubber ring153and the second rubber ring163, closer contact can be achieved between the contact surfaces of the cylinder141and the rear stepped sleeve157, between the contact surfaces of the tool holder guide139and the second rubber ring163and between the contact surfaces of the component parts of the impact absorption mechanism135. As a result, sealing performance of sealing the front bore space173are enhanced, so that the efficiency of the idle driving prevention mechanism171can be improved. Further, in this embodiment, the front stepped sleeve155and the rear stepped sleeve157have the same shape and are disposed in symmetry on the both sides of the first rubber ring153. Therefore, proper installation of the front and rear stepped sleeves155,157is ensured, so that ease of installation can be improved. Further, advantageously, the annular portion155aof the front stepped sleeve155can be utilized as a member for transmitting an impact, and the annular portion157aof the rear stepped sleeve157as a member for preventing displacement of the non-return valve in the form of the O-ring177.

Further, in this embodiment, the electric hammer is described as a representative example of the impact tool. However, the invention can also be applied to a hammer drill in which the hammer bit119performs a linear striking movement and a rotation in the circumferential direction.

DESCRIPTION OF NUMERALS