Patent Grant
8991517
1. Field of the Invention
The invention relates to an impact tool for performing a linear hammering operation on a workpiece, and more particularly to a technique for cushioning a reaction force during hammering operation.
2. Description of the Related Art
Hammering operation by an impact tool is performed with a hammer bit being pressed against a workpiece by application of user's forward pressing force to a tool body. At this time, the hammer bit is pushed to the tool body side (rearward) and an impact bolt is retracted together with the hammer bit and comes in contact with a tool body side component.
By such contact, the tool body is positioned with respect to the workpiece. In this state, when the hammer bit performs a striking movement, the hammer bit is caused to rebound by receiving a reaction force from the workpiece and the reaction force is transmitted to the tool body. Therefore, a reaction force cushioning mechanism for cushioning the striking reaction force is provided in prior art impact tools. For example, Japanese non-examined laid-open Patent Publication No. 2008-279587 discloses such an impact tool.
In the known impact tool, however, further improvement is desired to realize size reduction.
Accordingly, it is an object of the invention to provide an effective technique for realizing size reduction while providing an effect of cushioning a striking reaction force caused during operation, in an impact tool.
In order to solve the above-described problem, in a preferred embodiment according to the invention, an impact tool performs a predetermined operation on a workpiece at least by an axial linear movement of a tool bit which is mounted in a front end region of a tool body. The impact tool includes a reaction force transmitting member, a first elastic member and a second elastic member. The reaction force transmitting member is arranged to be movable in an axial direction of the tool bit and moves rearward by receiving a striking reaction force which is caused when the tool bit strikes the workpiece. The first elastic member biases the reaction force transmitting member forward. The second elastic member is pushed by the reaction force transmitting member and compressively deforms, thereby cushioning the striking reaction force, when the reaction force transmitting member moves rearward by receiving the striking reaction force. The “predetermined operation” in this invention suitably includes not only a hammering operation in which the tool bit performs only striking movement in its axial direction, but a hammer drill operation in which it performs striking movement in its axial direction and a rotation around its axis, The “first and second elastic members” in this invention typically comprise a compression coil spring, but suitably include rubber.
According to the preferred embodiment of the invention, an initial load of the first elastic member is set to be smaller than an initial load of the second elastic member. In operation, when a user presses the tool bit against the workpiece, the reaction force transmitting member is pushed by the tool bit and compresses the first elastic member, while it comes in contact with the second elastic member in an incompressible state, so that it is placed in a predetermined working position in the longitudinal direction. When the reaction force transmitting member receives the striking reaction force in the working position, the reaction force transmitting member moves rearward in the axial direction of the tool bit and compressively deforms the second elastic member, thereby cushioning the striking reaction force. The first and second elastic members are arranged in tandem in the axial direction of the tool bit. The “initial load” here refers to a load which is applied to the first and second elastic members in the direction of compression in advance and under which the elastic members are mounted. In this case, the initial load of the second elastic member is set to be larger than the user's normal pressing force of pressing the tool bit against the workpiece.
According to this invention, in prior to operation, when the tool bit is pressed against the workpiece and moved rearward, the reaction force transmitting member is pushed by the tool bit and compresses the first elastic member, and also comes in contact with the second elastic member in an incompressible state, so that the reaction force transmitting member is placed in a predetermined working position in the longitudinal direction. Thus, the tool body is positioned with respect to the workpiece. In this state, when the tool bit strikes the workpiece and receives the reaction force, the striking reaction force is transmitted from the tool bit to the reaction force transmitting member and the reaction force transmitting member is moved rearward. When moved rearward, the reaction force transmitting member pushes the second elastic member and compressively deforms it. As a result, the striking reaction force is cushioned, so that low-vibration impact tool can be realized.
According to this invention, with the construction in which the first and second elastic members are arranged in tandem in the axial direction of the tool bit, compared with the construction in which they are arranged in parallel, the size can be reduced in a direction (radial direction) transverse to the axial direction of the tool bit.
According to a further embodiment of the impact tool of the invention, the impact tool further includes a striking element that linearly moves to linearly drive the tool bit, and a cylinder that houses the striking element. Further, the cylinder receives a force acting upon the second elastic member.
According to this invention, with the construction in which the cylinder receives a force acting upon the second elastic member, the second elastic member can be held in noncontact with the housing which forms the tool body. Specifically, with the construction in which the second elastic member is mounted to the cylinder, the second elastic member can be first mounted to the cylinder and then mounted to the housing. Therefore, compared with a construction in which the second elastic member is directly mounted to the housing, mounting of the second elastic member can be facilitated, so that ease of mounting can be enhanced.
According to a further embodiment of the impact tool of the invention, the impact tool further includes a striking element that linearly moves to linearly drive the tool bit, and a cylinder that houses the striking element, and the reaction force transmitting member comprises a cylindrical member. Further, the cylindrical member and the first elastic member are arranged in parallel such that the first elastic member is disposed inward of the cylindrical member in a radial direction of the cylinder, in a predetermined region on the cylinder in the axial direction of the tool bit.
In a construction in which the cylindrical member in the form of the reaction force transmitting member is fitted on the cylinder, the cylinder and the cylindrical member are provided with respective air vents for air supply and exhaust which provide communication between a cylinder inner space formed in front of the striking element and the outside. In this case, it must be constructed such that the air vent of the cylinder and the air vent of the cylindrical member are normally aligned with each other. In this invention, however, with the construction in which the first elastic member is disposed between the cylinder and the cylindrical member, a clearance for installing the first elastic member is provided between the cylinder and the cylindrical member, so that the air vent of the cylinder and the air vent of the cylindrical member communicate with each other through the clearance. Therefore, an additional structure for aligning the air vent of the cylinder and the air vent of the cylindrical member can be dispensed with.
According to a further embodiment of the impact tool of the invention, the impact tool further includes a striking element that linearly moves to linearly drive the tool bit, and a cylinder that houses the striking element. The reaction force transmitting member comprises a cylindrical member that is slidably fitted on the cylinder. Further, the cylindrical member has a passage that provides communication between a cylinder inner space formed in front of the striking element and the outside, and a nonreturn valve that allows air flow from the cylinder inner space to the outside through the passage and blocks air flow in the opposite direction. When the tool bit is pressed against the workpiece by the user and the cylindrical member is placed in a predetermined working position, the passage is closed by the cylinder so that the nonreturn valve is deactivated, and when the tool bit pressed against the workpiece is released and the cylindrical member is moved forward to an initial position by the biasing force of the first elastic member, the cylinder no longer closes the passage so that the nonreturn valve is allowed to activate.
According to this invention, when the tool bit is not pressed against the workpiece, the nonreturn valve is allowed to activate. In this state, when the striking element moves forward, air within the cylinder inner space in front of the striking element is discharged to the outside through the passage and the nonreturn valve. Thereafter, when the striking element is going to move rearward, the nonreturn valve blocks inflow of outside air into the cylinder inner space, so that negative pressure is caused in the cylinder inner space. As a result, the striking element is held in the forward position, so that idle driving is prevented. On the other hand, during actual operation in which the impact tool performs an operation with the tool bit being pressed against the workpiece, the nonreturn valve is deactivated. Therefore, unnecessary movement of the nonreturn valve can be reduced, so that durability of the nonreturn valve can be improved.
According to this invention, an effective technique for realizing size reduction while providing an effect of cushioning a striking reaction force caused during operation, is provided in an impact tool. Other objects, features and advantages of the invention will be readily understood after reading the following detailed description together with the accompanying drawings and the claims.
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 method 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.
An embodiment of the invention is now described with reference to
The body 103 includes a motor housing 105 that houses a driving motor 111, and a gear housing 107 that includes a barrel 106 and houses a motion converting mechanism 113, a striking mechanism 115 and a power transmitting mechanism 117. The driving motor 111 is disposed such that its axis of rotation runs in a vertical direction substantially perpendicular to the longitudinal direction of the body 103 (the axial direction of the hammer bit 119). Rotating power of the driving motor 111 is appropriately converted into linear motion by the motion converting mechanism 113 and then transmitted to the striking mechanism 115. As a result, an impact force is generated in the axial direction of the hammer bit 119 via the striking mechanism 115. The motion converting mechanism 113 and the striking mechanism 115 form a striking mechanism part. Further, the speed of the rotating power of the driving motor 111 is appropriately reduced by the power transmitting mechanism 117 and then transmitted to the hammer bit 119 via the tool holder 137, so that the hammer bit 119 is caused to rotate in its circumferential direction. The driving motor 111 is driven when a user depresses a trigger 109a disposed on the handgrip 109.
The motion converting mechanism 113 mainly includes a crank mechanism. The crank mechanism is constructed such that a driving element in the form of a piston 129 forming a final movable member of the crank mechanism linearly moves in the axial direction of the hammer bit within a cylinder 141 when the crank mechanism is rotationally driven by the driving motor 111. The power transmitting mechanism 117 mainly includes a gear speed reducing mechanism comprising a plurality of gears. The power transmitting mechanism 117 transmits the rotating force of the driving motor 111 to the tool holder 137, so that the tool holder 137 is caused to rotate in a vertical plane and thus the hammer bit 119 held by the tool holder 137 rotates, The constructions of the motion converting mechanism 113 and the power transmitting mechanism 117 are well-known in the art and therefore they are not described in further detail.
As shown in
In the hammer drill 101 constructed as described above, when the driving motor 111 is driven, a striking force is applied to the hammer bit 119 in the axial direction from the motion converting mechanism 113 via the striking mechanism 115, and a rotating force is applied to the hammer bit 119 in the circumferential direction via the power transmitting mechanism 117. Thus, the hammer bit 119 held by a bit holding device 104 performs a hammering movement in the axial direction and a drilling movement in the circumferential direction, so that a hammer drill operation (drilling) is performed on a workpiece (concrete) which is not shown. Further, the hammer drill 101 can be appropriately switched between mode of hammer drill operation by hammering movement and drilling movement in the circumferential direction as described above and mode of hammering operation in which only a striking force in the axial direction is applied to the hammer bit 119. However, this is not directly related to the invention, and therefore its detailed description is omitted.
In the hammer drill 101, during operation, when the hammer bit 119 is pressed against the workpiece by the user's pressing force applied forward to the body 103, the impact bolt 145 is pushed rearward (toward the piston 129) together with the hammer bit 119 and comes into contact with a body-side member. As a result, the body 103 is positioned with respect to the workpiece. In this embodiment, such positioning is effected by a compression coil spring 171 for cushioning a reaction force, via a positioning member 151 and a slide sleeve 161 for prevention of idle driving. The slide sleeve 161 and the compression coil spring 171 are features that correspond to the “reaction force transmitting member” and the “second elastic member”, respectively, according to this invention.
The positioning member 151 is a unit part including a rubber ring 153, a front-side hard metal washer 155 joined to the axial front side of the rubber ring 153, and a rear-side hard metal washer 157 joined to the axial rear side of the rubber ring 153. The positioning member 151 is loosely fitted onto a small-diameter portion 145b of the impact bolt 145. The impact bolt 145 has a stepped, cylindrical form having a large-diameter portion 145a that is slidably fitted in the cylindrical portion of the tool holder 137 and a small-diameter portion 145b formed on the rear side of the large-diameter portion 145a, The impact bolt 145 has a tapered portion 145c formed between the outer circumferential surface of the large-diameter portion 145a and the outer circumferential surface of the small-diameter portion 145b.
The slide sleeve 161 is a cylindrical member having a stepped bore formed by a small-diameter front portion and a large-diameter rear portion in the longitudinal direction. The bore small-diameter region of the slide sleeve 161 is fitted on a front end outer surface of the cylinder 141 and can slide in the axial direction of the hammer bit. A predetermined clearance C is provided between a bore large-diameter region of the slide sleeve 161 and an outer surface region of the cylinder. A sleeve biasing spring (coil spring) 163 is disposed in the clearance C. The sleeve biasing spring 163 constantly biases the slide sleeve 161 forward, and an axial rear end of the sleeve biasing spring 163 is held in contact with a retaining ring 164 fixed on the outer surface of the cylinder 141, and an axial front end of the sleeve biasing spring 163 is held in contact with a stepped part 161a between the bore large-diameter region and the bore small-diameter region of the slide sleeve 161. Thus, a front end of the slide sleeve 161 biased forward by the sleeve biasing spring 163 is held in contact with the rear metal washer 157 of the positioning member 151. The sleeve biasing spring 163 is a feature that corresponds to the “first elastic member” according to this invention.
The compression coil spring 171 for cushioning a reaction force is mounted on the cylinder 141 via front and rear spring receiving rings 173, 175. The front spring receiving ring 173 is fitted on the cylinder 141 and held in contact with a rear surface of the retaining ring 164 by the spring force of the compression coil spring 171, so that the front spring receiving ring 173 is prevented from moving further forward. The rear spring receiving ring 175 is fitted on the cylinder 141 and held in contact with a stepped part 141c formed on the outer surface of the cylinder 141, so that the rear spring receiving ring 175 is prevented from moving further rearward. The compression coil spring 171 is elastically mounted in a pre-compressed state between the front spring receiving ring 173 and the rear spring receiving ring 175. At this time, the initial load of the compression coil spring 171 is set to be larger than the pressing force of an ordinary user pressing the hammer bit 119 against the workpiece. Further, the above-described sleeve biasing spring 163 is also mounted in a pre-compressed state, but its initial load is smaller than the compression coil spring 171. In this embodiment, the initial load of the compression coil spring 171 is set to be 20 to 30 kgf, and the initial load of the sleeve biasing spring 163 is set to be 3 to 5 kgf. Further, the front spring receiving ring 173 has a larger diameter than the retaining ring 164, and an outer region of the front spring receiving ring 173 juts radially outward of the retaining ring 164.
Under unloaded conditions in which the hammer bit 119 is not pressed against the workpiece, as shown in
The air chamber 141a for driving the striker 143 by the action of air spring communicates with the outside via a first air vent 165 which is formed in the cylinder 141 for prevention of idle driving. Under unloaded conditions in which the hammer bit 119 is not pressed against the workpiece, or when the impact bolt 145 is not pushed in rearward (rightward as viewed in
Thus, the first air vent 165 of the air chamber 141a is opened and closed by the striker 143. The action of the air spring is disabled when the first air vent 165 is opened, while it is enabled when the first air vent 165 is closed.
A closed front air chamber 141b is formed in front of the striker 143 on the side opposite the air chamber 141a and surrounded by the striker 143, the cylinder 141, the slide sleeve 161, the positioning member 151 and the impact bolt 145. The front air chamber 141b communicates with the outside via the second air vent 166 which is formed in the cylinder 141 for air supply and exhaust and via the third air vent 167 which is formed in the slide sleeve 161. Opening and closing of the second air vent 166 for air supply and exhaust are controlled by the position of the striker 143. Specifically, during operation of the hammer drill 101, when the striker 143 is situated rearward of a predetermined reference position (substantially near to the impact bolt 145), the front air chamber 141b communicates with the outside via the second air vent 166 and the third air vent 167, so that air supply and exhaust of the front air chamber 141b are allowed. On the other hand, when the striker 143 is moved forward past the reference position, the communication between the front air chamber 141b and the outside is interrupted, so that the air supply and exhaust of the front air chamber 141b are prohibited. As a result, the movement of the striker 143 is delayed with respect to the movement of the piston 129. Further, the second air vent 166 and the third air vent 167 communicate with each other through the clearance C between the outer surface of the cylinder 141 and the bore large-diameter region of the slide sleeve 161.
Further, a fourth air vent 168 and an O-ring 169 are provided in the front end region (bore small-diameter region) of the slide sleeve 161. The fourth air vent 168 is provided for prevention of idle driving and provides communication between the inside and outside of the front air chamber 141b. The O-ring 169 closes the fourth air vent 168 from the outer surface of the slide sleeve 161. The O-ring 169 allows air flow from the front air chamber 141b to the outside through the fourth air vent 168 and blocks air flow in the opposite direction. The fourth air vent 168 is formed in a position such that it faces the front air chamber 141b under unloaded conditions in which the hammer bit 119 is not pressed against the workpiece, while it is closed by the outer surface of the cylinder 141 when the slide sleeve 161 is moved rearward against the biasing force of the sleeve biasing spring 163 under loaded conditions in which the hammer bit 119 is pressed against the workpiece. The front air chamber 141b, the fourth air vent 168 and the O-ring 169 are features that correspond to the “cylinder inner space”, the “passage” and the “nonreturn valve”, respectively, according to this invention.
Operation of the hammer drill 101 constructed as described above is now explained. When the driving motor 111 is driven, the piston 129 of the crank mechanism which forms the motion converting mechanism 113 is caused to linearly slide within the cylinder 141. At this time, under unloaded conditions in which the hammer bit 119 is not pressed against the workpiece, as shown in
On the other hand, under loaded conditions in which the hammer bit 119 is pressed against the workpiece, as shown in
During the above-described operation, when the hammer bit 119 performs striking movement on the workpiece and the hammer bit 119 is caused to rebound by the reaction force from the workpiece, a force caused by this rebound, or striking reaction force moves the hammer bit 119, the impact bolt 145, the positioning member 151 and the slide sleeve 161 rearward and elastically deforms (compresses) the compression coil spring 171. Specifically, the striking reaction force caused by rebound of the hammer bit 119 is efficiently cushioned by elastic deformation of the compression coil spring 171, so that transmission of the reaction force to the body 103 is reduced. At this time, a flange part 161b which extends radially inward from the slide sleeve 161 faces the front end surface of the cylinder 141 with a predetermined clearance therebetween and can come into contact with it, so that the maximum retracted position of the slide sleeve 161 is defined. Therefore, the reaction force cushioning action of the compression coil spring 171 is effected within the range of the above-mentioned clearance.
As described above, according to this embodiment, by provision of the mechanism of cushioning the striking reaction force from the hammer bit 119 by the compression coil spring 171 via the slide sleeve 161 for prevention of idle driving, an idle driving prevention effect and a vibration reducing effect can be obtained.
Further, according to this embodiment, the compression coil spring 171 is mounted on the cylinder 141 via the front and rear spring receiving rings 173, 175. Therefore, the cylinder 141 and the compression coil spring 171 are assembled into one piece, so that the cylinder 141 and the compression coil spring 171 can be mounted and removed from the gear housing 107 as one piece.
Thus, ease of mounting or repairing can be enhanced.
Further, in this embodiment, during operation in which the hammer bit 119 is pressed against the workpiece and the slide sleeve 161 is pushed rearward, the fourth air vent 168 is situated in a position to face the outer surface of the cylinder 141 and closed by the outer surface of the cylinder 141. Specifically, during actual operation in which the hammer drill 101 performs an operation, the nonreturn valve in the form of the O-ring 169 is held at a standstill (deactivated). With this construction, unnecessary movement of the O-ring 169 can be reduced during actual operation, so that durability of the O-ring 169 can be improved.
Further, according to this embodiment, the clearance C is provided between the outer surface of the cylinder 141 and the inner surface of the slide sleeve 161, and the second air vent 166 of the cylinder 161 and the third air vent 167 of the slide sleeve 161 communicate with each other through the clearance C. With this construction, reliability of air supply and exhaust can be enhanced without need of taking measures to align the second air vent 166 and the third air vent 167. Further, with the construction in which the sleeve biasing spring 163 is arranged in parallel within the clearance C provided between the outer surface of the cylinder 141 and the inner surface of the slide sleeve 161, size increase of the body 103 in the longitudinal direction can be avoided.
Further, according to this embodiment, with the construction in which the sleeve biasing spring 163 and the compression coil spring 171 are arranged in tandem, compared with a construction in which they are arranged in parallel, the size of the body 103 can be reduced in the radial direction. Further, with the construction in which the outside diameter of the slide sleeve 161 is substantially equal to the outside diameter of the compression coil spring 171, although the slide sleeve 161 and the sleeve biasing spring 163 are arranged in parallel, size increase of the body 103 in the radial direction can be avoided.
In the above-described embodiment, as a representative example of the impact tool, the hammer drill 101 was described in which the hammer bit 119 can be switched between mode of hammering operation by hammering movement of the hammer bit 119 and mode of hammer drill operation by hammering movement in the axial direction and drilling movement in the circumferential direction. However, the invention can also be applied to an electric hammer in which the hammer bit 119 performs only hammering movement in its axial direction.
According to the aspect of the invention, following features can be provided.
“The impact tool as defined in any one of claims 1 to 4, wherein the cylinder includes a front spring receiving ring that is prevented from moving forward and a rear spring receiving ring that is prevented from moving rearward, and the second elastic member comprises a compression coil spring and is elastically disposed in a pre-compressed state between the front spring receiving ring and the rear spring receiving ring.”
“The impact tool as defined in (1), wherein the cylinder includes a retaining ring which is held in contact with the front spring receiving ring and prevents the front spring receiving ring from moving forward, while receiving a rear end of the first elastic member, and the front spring receiving ring has a larger diameter than the retaining ring, and when the user presses the tool bit against the workpiece, a rear end surface of the reaction force transmitting member contacts a front surface of an outer region of the front spring receiving ring.”
| Number | Date | Country | Kind |
|---|---|---|---|
| 2010-173845 | Aug 2010 | JP | national |
| Number | Name | Date | Kind |
|---|---|---|---|
| 2875731 | Settles et al. | Mar 1959 | A |
| 3788404 | Koudelka et al. | Jan 1974 | A |
| 5975217 | Frenzel et al. | Nov 1999 | A |
| 20080283264 | Ikuta et al. | Nov 2008 | A1 |
| 20080283265 | Ikuta | Nov 2008 | A1 |
| Number | Date | Country |
|---|---|---|
| A-2008-194762 | Aug 2008 | JP |
| A-2008-279587 | Nov 2008 | JP |
| Entry |
|---|
| Nov. 21, 2011 Extended Search Report issued in European Patent Application No. 11175973.4. |
| Number | Date | Country | |
|---|---|---|---|
| 20120024555 A1 | Feb 2012 | US |
