Impact tool

An impact tool includes a tubular tool holder, a hammering mechanism, a resistor, and a biasing member. An impact element moves forward and rearward in conjunction with a piston. An intermediate element is housed movable back and forth between the impact element and a tip tool. The intermediate element abuts on a rear end of the tip tool to indirectly transmit a striking force from the impact element to the tip tool in a normal striking. The resistor is configured to abut on at least one of the intermediate element and the tip tool to apply a resistance to a front-rear movement of at least one of the intermediate element and the tip tool in a non-striking state. The biasing member disposed on the tool holder biases the resistor to a side of at least one of the intermediate element and the tip tool.

BACKGROUND

This application claims the benefit of Japanese Patent Application Number 2018-076311 filed on Apr. 11, 2018 and Japanese Patent Application Number 2018-243287 filed on Dec. 26, 2018, the entirety of which is incorporated by reference.

TECHNICAL FIELD

The disclosure relates to an impact tool such as an electric hammer and a hammer drill.

RELATED ART

An impact tool, such as an electric hammer and a hammer drill, ensures hammering operation by transforming rotation from a motor into forward and rearward movement of a piston with a crank mechanism or the like to indirectly hammer a rear end of a tip tool mounted on a tool holder via an intermediate element with an impact element that moves forward and rearward inside a cylinder or a tool holder in conjunction with the piston.

As the impact tool, the following impact tool has been known. The impact tool includes a no-load striking prevention mechanism such that the intermediate element is not stricken with the impact element, even though the piston is reciprocated in a state where the tip tool is not mounted on the tool holder and a state where the tip tool is not pushed against a surface to be processed (hereinafter, they are referred to as “non-striking state”). For example, Japanese Patent No. 3369844 discloses a locking O-ring disposed on a distal end of a cylinder, and a circular cone formed on an intermediate element. In the non-striking state, the locking O-ring is engaged with the circular cone of the intermediate element which has advanced with a first no-load striking compared with in a normal striking, which applies resistance to front-rear movement of the intermediate element. Thus, the intermediate element is restricted to move toward the impact element, thereby preventing the subsequent no-load striking.

However, in Japanese Patent No. 3369844, the O-ring as an elastic body directly performs the movement restriction on the intermediate element. Thus, the O-ring may be abraded or deteriorated by repeating contact with the intermediate element to reduce a resistive power applied to the intermediate element, thus possibly being less able to provide a no-load striking prevention function.

Therefore, it is an object of the disclosure to provide an impact tool configured to provide a stable no-load striking prevention function even though movement restriction of an intermediate element is ensured.

SUMMARY

In order to achieve the above-described object, there is provided an impact tool according to the disclosure. The impact tool is configured to include a tubular tool holder, a striking mechanism, a resistor, and a biasing member. The tool holder holds a tip tool. The striking mechanism is disposed inside the tool holder. The striking mechanism includes a piston, an impact element, and an intermediate element. The piston moves forward and rearward in accordance with rotation from a motor. The impact element moves forward and rearward in conjunction with the piston. The intermediate element is housed movable back and forth between the impact element and the tip tool. The intermediate element abuts on a rear end of the tip tool to indirectly transmit a striking force from the impact element to the tip tool in a normal striking. The resistor is disposed on the tool holder. The resistor is configured to abut on at least one of the intermediate element and the tip tool to apply a resistance to a front-rear movement of at least one of the intermediate element and the tip tool in a non-striking state. The biasing member is disposed on the tool holder. The biasing member biases the resistor toward at least one of the intermediate element and the tip tool.

“Non-striking state” means a state where the tip tool is not mounted on the tool holder as described above and a state where the tip tool is not pushed against a surface to be processed even though the tip tool is mounted on the tool holder.

In the disclosure, the resistor is preferably disposed at a position where the resistor abuts on the intermediate element that has advanced in a no-load striking from a rear to restrict a rearward movement of the intermediate element.

The resistor is preferably made of metal.

The resistor preferably has a taper shape tapered off toward an inside of the tool holder.

The resistor preferably has a distal end on which a hemispherical portion is formed.

The resistor is preferably disposed with passing through the tool holder in a radial direction to be movable in the radial direction. The biasing member preferably projects and biases the resistor from an outer side to an inner side of the tool holder.

The biasing member is preferably a C-shaped leaf spring wound around the tool holder.

The resistor preferably abuts on the intermediate element. A resistor abutting portion having a diameter smaller than a diameter of a slidingly-contact portion guided by an inner peripheral surface of the tool holder is preferably formed on a rear portion of the intermediate element.

A non-guide surface without slidingly contacting the impact element that has advanced in a no-load striking is preferably formed on an inner peripheral surface of the tool holder.

An air vent hole is preferably formed with passing through the tool holder at a position of the non-guide surface. The air vent hole is preferably communicated from an inside to an outside of the tool holder.

A front end surface of the impact element and a rear end surface of the intermediate element preferably abut on one another when the impact element advances. The front end surface of the impact element and the rear end surface of the intermediate element preferably have curved convex surfaces bulging in a direction facing one another.

The resistor is preferably disposed at a position where the resistor abuts on a retaining groove of the tip tool that has advanced in a no-load striking to restrict a rearward movement of the tip tool.

The tool holder preferably has a distal end portion on which a ball is engaged with the retaining groove to retain the tip tool and prevent the tip tool from rotating. The resistor is preferably arranged ahead of the ball. The resistor is preferably positioned inside the retaining groove at a position where the ball abuts on a rear end of the retaining groove of the tip tool that has advanced in the no-load striking.

The resistor is preferably a metallic ball.

According to the disclosure, the resistor, which is configured to abut on the intermediate element and/or the tip tool to apply the resistance to its front-rear movement in the non-striking state, and the biasing member, which biases the resistor to a side of the intermediate element and/or the tip tool, are disposed on the tool holder. Thus, the disclosure is configured to reduce the momentum of the intermediate element and/or the tip tool that advances with the no-load striking to restrain bounce, thus preventing the subsequent no-load striking. The use of the biasing member separately from the resistor can eliminate the need to use an elastic material as the resistor, reducing possibility of abrasion and deterioration. Accordingly, even though the movement restriction of the intermediate element and/or the tip tool is ensured, stable no-load striking prevention function can be provided.

When the resistor is disposed at the position where the resistor abuts on the intermediate element that has advanced in the no-load striking from the rear to restrict the rearward movement of the intermediate element, the function to restrict the retreat of the intermediate element can be added to the resistor having the function to reduce the momentum of the intermediate element, thus more certainly ensuring the no-load striking prevention.

The metallic resistor eliminates the possibility of the abrasion and the deterioration to improve durability.

The resistor having the taper shape tapered off toward the inside of the tool holder facilitates setting of the projecting position toward the inside of the tool holder, and the resistor can be assembled to the tool holder regardless of directionality.

When the resistor is disposed with passing through the tool holder in the radial direction to be movable in this radial direction and the biasing member is configured to project and bias the resistor from an outer side to an inner side of the tool holder, the resistor can be easily projected and biased to the inside of the tool holder.

When the biasing member is the C-shaped leaf spring wound around the tool holder, the biasing member can be easily assembled to the tool holder.

When the resistor is considered as one abutting on the intermediate element and the resistor abutting portion having the diameter smaller than that of the slidingly-contact portion guided by the inner peripheral surface of the tool holder is formed on the back portion of the intermediate element, the resistance can be applied without making the resistor abut on the slidingly-contact portion.

When the non-guide surface is formed on the inner peripheral surface of the tool holder so as not to slidingly contact the impact element that has advanced in the no-load striking, the impact element is moved with the first striking and located inside with respect to the non-guide surface. As a result, the impact element becomes likely to be inclined from the axis line of advancing and retreating movement in the normal striking. Thus, the striking force of the first no-load striking against the intermediate element can be weakened to reduce the momentum of the forward movement of the intermediate element. Accordingly, the certain no-load striking prevention is ensured.

When the front end surface of the impact element and the rear end surface of the intermediate element that abut on one another have the curved convex surfaces bulging in a direction facing one another, even though the slight inclination occurs on the impact element, appropriate abutment of the front shaft portion on the rear shaft portion is ensured, thus not applying an excessive load to the intermediate element.

When the resistor is disposed at the position where the resistor abuts on the retaining groove of the tip tool that has advanced in the no-load striking to restrict the rearward movement of the tip tool, the resistance can be easily applied to the tip tool using the retaining groove, thus ensuring effective no-load striking prevention.

DETAILED DESCRIPTION

The following describes embodiments of the disclosure based on the drawings.

FIG. 1is a center vertical cross-sectional view illustrating an exemplary hammer drill1as an impact tool.

In the hammer drill1, a motor housing3, which houses a motor4with an output shaft5disposed upward, is coupled to a front lower portion of a main body housing2in an up and down direction. Above the motor housing3, the hammer drill1internally includes a gear housing6that houses a crankshaft7and an intermediate shaft8each engaged with the output shaft5. A front housing9, which houses a tubular tool holder10disposed forward, is assembled on a front side of the gear housing6. A handle housing11is coupled to a back portion of the main body housing2. A housing cover12, which covers the front housing9, is coupled to a front portion of the main body housing2.

The intermediate shaft8is engaged with a bevel gear13disposed on a rear end of the tool holder10. A tip tool T such as a drill bit is mountable on a distal end of the tool holder10with an operation sleeve14. The handle housing11includes a switch15and a switch lever16. A power supply cord17is connected to a lower portion of the handle housing11.

The tool holder10internally includes a piston20that is reciprocated with being coupled to an eccentric pin18of the crankshaft7via a coupling rod19. A striker (impact element)22is housed via an air chamber21ahead of the piston20, and an intermediate element23is housed ahead of the striker22, thus forming a striking mechanism. As illustrated inFIG. 2, the striker22has a front shaft portion24projecting forward at a center of a front portion. The front shaft portion24has a front surface that is a spherical surface25as a convex surface slightly bulging forward.

The intermediate element23has an intermediate portion that is a slidingly-contact portion26having a large diameter, which is guided by a front guide surface36described later. The intermediate element23has a rear portion that is a pin abutting portion27as a resistor abutting portion having a diameter smaller than that of the slidingly-contact portion26. The pin abutting portion27has a rear portion that is a tapered portion28having a diameter gradually decreasing rearward. The tapered portion28has a center on which a rear shaft portion29projecting rearward is formed. The rear shaft portion29has a rear surface that is a spherical surface30as a convex surface slightly projecting rearward.

The tool holder10includes a rear guide surface35and the front guide surface36are each formed on its inner peripheral surface. The rear guide surface35houses the piston20and the striker22. The front guide surface36houses the intermediate element23and has a diameter smaller than that of the rear guide surface35. A non-guide surface37is partially disposed ahead of an advance position of the striker22in normal striking on the rear guide surface35. The non-guide surface37has a diameter larger than an inner diameter of the rear guide surface35and does not contact an outer peripheral surface of the striker22that has advanced in no-load striking. Air vent holes38,38, which communicate the inside with the outside of the tool holder10, are formed with passing through the tool holder10at a position of the non-guide surface37.

Further, a front receiving ring39, through which the rear shaft portion29of the intermediate element23passes to receive a rear surface of the intermediate element23, is disposed on a front end of the rear guide surface35inside the tool holder10. A gripping ring40, which grips the front shaft portion24of the striker22when the striker22advances with the no-load striking, is disposed at the rear of the front receiving ring39. A rear receiving ring41through which the front shaft portion24passes to receive a front surface of the striker22is disposed at the rear of the gripping ring40.

The front receiving ring39, gripping ring40, and rear receiving ring41are positioned from front to rear. In a state where the front receiving ring39abuts on a stepped portion42formed between the rear guide surface35and the front guide surface36to restrict its forward movement, the gripping ring40and the rear receiving ring41are housed in this order. The retreat of the rear receiving ring41is restricted by a locking ring43locked to the rear guide surface35.

A through-hole45having a taper shape tapered off from the outside toward the inside in a radial direction is formed in the radial direction at a rear end position of the front guide surface36on the tool holder10. A resistance pin46as a resistor is inserted into the through-hole45. As illustrated inFIG. 3, the resistance pin46is a metallic shaft body formed into a taper shape that is tapered off in accordance with the through-hole45. A hemispherical portion47is continuously formed on a distal end, which is tapered off, of the resistance pin46, while a protrusion portion48having a small diameter is formed on a base end side of the resistance pin46. The protrusion portion48axially has a constant diameter.

A leaf spring49as a biasing member is externally mounted on an outer periphery of the tool holder10at a position of the resistance pin46. The leaf spring49is made such that a strip-shaped metal plate is folded into a C shape. A slit50is formed on a center in a width direction of the leaf spring49excluding both ends in a longitudinal direction. A through hole51is formed on one end part portion of the leaf spring49.

In state where the resistance pin46has been inserted into the through-hole45from the hemispherical portion47, the leaf spring49is externally mounted on the outer periphery of the tool holder10with the protrusion portion48of the resistance pin46having been inserted into the through hole51. Accordingly, due to an elasticity of the leaf spring49, the resistance pin46is pushed axially inward of the tool holder10and biased to a projecting position where the hemispherical portion47is projected inward from the through-hole45. In a state where the resistance pin46does not abut on the pin abutting portion27of the intermediate element23, as illustrated inFIG. 5, a distal end of the hemispherical portion47projects axially inward of the tool holder10with respect to an outer peripheral surface of the pin abutting portion27of the intermediate element23.

In the hammer drill1configured as described above, with a change lever (not illustrated) disposed on a left side surface of the main body housing2, it is possible to select a hammer mode that rotates the crankshaft7to strike the tip tool T, a drill mode that rotates the intermediate shaft8to rotate the tip tool T together with the tool holder10, and a hammer drill mode that simultaneously operates the crankshaft7and the intermediate shaft8to strike and rotate the tip tool T.

Here, the tip tool T is inserted and mounted from the distal end of the tool holder10. When a distal end of the tip tool T is pushed against the surface to be processed, the tip tool T is pushed to retreat the intermediate element23. Subsequently, the intermediate element23abuts on the front receiving ring39, and thus, the push is restricted at a retreated position where the rear shaft portion29is projected inside the rear receiving ring41. When the intermediate element23retreats, the hemispherical portion47, which is projecting inside the tool holder10, of the resistance pin46abuts on the tapered portion28. The hemispherical portion47in the abutting state relatively moves to an outer peripheral side of the tapered portion28directly as the intermediate element23retreats, thus retreating the resistance pin46outside in the radial direction inside the through-hole45against the bias of the leaf spring49. When the resistance pin46is positioned at the retreated position of the intermediate element23, the hemispherical portion47is pushed against the outer periphery of the pin abutting portion27as illustrated inFIGS. 1 and 2.

Next, when a push-in operation is performed on the switch lever16to turn on the switch15in a state where the hammer mode or the hammer drill mode is selected with the change lever, the motor4is driven to rotate the output shaft5, thus rotating the crankshaft7. Accordingly, eccentric motion of the eccentric pin18moves the piston20forward and rearward via the coupling rod19to move the striker22forward and rearward via the air chamber21. Thus, the front shaft portion24of the striker22strikes the rear shaft portion29of the intermediate element23inside the rear receiving ring41. Consequently, the tip tool T is indirectly stricken by the striker22via the intermediate element23to enable the tip tool T to, for example, cut the surface to be processed.

On the other hand, when the push-in operation is performed on the switch lever16in a non-striking state where the tip tool T is not pushed against the surface to be processed (or the tip tool T is not mounted on the tool holder10), as illustrated inFIGS. 4 and 5, first striking (no-load striking) by the striker22will move the intermediate element23forward from the retreated position. At this time, the intermediate element23advances in a state where the pin abutting portion27is pushed by the resistance pin46from an outside in the radial direction to receive the resistance. Thus, momentum of the forward movement is reduced to decrease a bounce after a front end of the intermediate element23collides against a front-side inner surface of the tool holder10. Even if the intermediate element23bounces, the hemispherical portion47of the resistance pin46, which has returned to the projecting position as the intermediate element23advances, is engaged with a peripheral edge of the tapered portion28from the rear. Thus, the intermediate element23is restricted from retreating here, and does not return to the retreated position. Therefore, the subsequent no-load striking is prevented.

The striker22that has advanced with the first no-load striking advances to a position where a distal end of the front shaft portion24reaches the inside of the gripping ring40. Here, a plurality of ventilation holes31,31. . . (FIG. 4) that are opened by the forward movement of the striker22are circumferentially formed on the tool holder10. The air chamber21is communicated with the outside of the tool holder10, thus losing action of air spring. Accordingly, the striker22is held at a position where the front end of the front shaft portion24is fitted to the gripping ring40, and conjunction with the piston20of the striker22is cut off.

Further, the non-guide surface37having a diameter larger than that of the striker22is formed on the rear guide surface35of the tool holder10. When the striker22advances with the first no-load striking, the striker22moves to locate inside with respect to the non-guide surface37, thereby losing forward movement guide by the rear guide surface35. Thus, the striker22becomes likely to be inclined from an axis line of the forward and rearward movement in the normal striking, weakening striking force itself with the first no-load striking against the intermediate element23. The spherical surfaces25and30each bulging in a direction facing one another are formed on the front end surface of the front shaft portion24of the striker22and the rear end surface of the rear shaft portion29of the intermediate element23. Thus, even though the slight inclination occurs on the striker22, appropriate abutment of the front shaft portion24on the rear shaft portion29is ensured.

With the hammer drill1as described above, the resistance pin46(resistor), which is configured to abut on the intermediate element23in the non-striking state to apply the resistance to the front-rear movement of the intermediate element23, and the leaf spring49(biasing member), which biases the resistance pin46to a side of the intermediate element23, are disposed on the tool holder10. When the intermediate element23advances with the no-load striking, the resistance pin46and the leaf spring49cause the intermediate element23to restrain its bouncing action by reducing the momentum, thus preventing the subsequent no-load striking. The use of the leaf spring49for biasing separately from the resistance pin46can eliminate the need to use an elastic material as the resistance pin46, thus reducing possibility of abrasion and deterioration. Accordingly, even though the movement restriction of the intermediate element23is ensured, stable no-load striking prevention function can be provided.

Especially here, the resistance pin46is disposed at a position where the resistance pin46abuts on the intermediate element23that has advanced in the no-load striking from the rear to restrict the rearward movement of the intermediate element23. Therefore, the function to restrict the retreat of the intermediate element23can be added to the resistance pin46having the function to reduce the momentum of the intermediate element23, thus more certainly ensuring the no-load striking prevention.

The metallic resistance pin46eliminates the possibility of the abrasion and the deterioration to improve durability.

Furthermore, the resistance pin46having the taper shape tapered off toward the inside of the tool holder10facilitates setting of the projecting position to the inside of the tool holder10and can be assembled to the tool holder10regardless of directionality.

In addition, the resistance pin46is disposed with passing through the tool holder10in the radial direction to be movable in this radial direction. The leaf spring49is configured to project and bias the resistance pin46from an outer side to an inner side of the tool holder10, which allows to easily project and bias the resistance pin46to the inside of the tool holder10.

The biasing member is the C-shaped leaf spring49wound around the tool holder10, thus being easily assembled to the tool holder10.

Furthermore, the pin abutting portion27having the diameter smaller than that of the slidingly-contact portion26guided by the front guide surface36of the tool holder10is formed on the back portion of the intermediate element23. Thus, the resistance can be applied without making the resistance pin46abut on the slidingly-contact portion26.

The non-guide surface37with which the striker22that has advanced in the no-load striking does not slidingly contact is formed on the inner peripheral surface of the tool holder10. The striker22moves with the first no-load striking to locate inside with respect to the non-guide surface37. As a result, the striker22becomes likely to be inclined from the axis line of the forward and rearward movement in the normal striking by moving with the first no-load striking to locate inside with respect to the non-guide surface37. Accordingly, the striking force of the first no-load striking against the intermediate element23can be weakened to reduce the momentum of the forward movement of the intermediate element23. Consequently, the certain no-load striking prevention is ensured.

Further, the spherical surfaces25and30bulging in the direction facing one another are formed on the front end surface of the striker22and the rear end surface of the intermediate element23that abut on one another when the striker22advances. Thus, even though the slight inclination occurs on the striker22, appropriate abutment of the front shaft portion24on the rear shaft portion29is ensured, thus not applying an excessive load to the intermediate element23.

The shape of the resistance pin is not limited to the taper shape in the above-described configuration, and can be changed as necessary such as having a constant diameter over the whole length in the axial direction. The resistor is not limited to have the pin shape, and for example, a ball and a roller can be employed. The number of resistors is not limited to one, and a plurality of resistors may be concentrically arranged on the tool holder. Furthermore, the resistor is allowed to be formed long in the circumferential direction of the tool holder to increase a contacted area with the intermediate element. As the material of the resistor, for example, ceramic and hard resin can be employed other than the metal.

In addition, the biasing member is not limited to the leaf spring, and for example, a wire wound around the tool holder and a plate spring that is not wound around the tool holder can be employed. The biasing member may be housed in a depressed groove formed on the outer periphery of the tool holder.

In the above-described configuration, the resistor abutting portion having the small diameter is formed on the rear portion of the intermediate element, but the resistor may abut on the slidingly-contact portion without the resistor abutting portion. The non-guide surface disposed on the inner peripheral surface of the tool holder also can be omitted. The curved convex surfaces formed on the front end surface of the striker and the rear end surface of the intermediate element may be, for example, not only directional curved convex surfaces, but also the spherical surfaces without the directionality, and need not be the curved convex surfaces.

In the above-described configuration, the resistor that applies the resistance to the intermediate element is disposed, but a resistor that applies the resistance to the tip tool may be disposed.

FIG. 6illustrates a hammer drill1A according to the modification example. First, a pair of balls56,56are disposed on a distal end portion55of the tool holder10inside the operation sleeve14. The balls56,56are held in elongate holes57,57drilled in the radial direction up to the distal end portion55with being configured to appear to an axial center of the distal end portion55. The balls56,56are pushed to the projecting position toward the axial center by a lock ring59inside the operation sleeve14. The lock ring59is biased to an advance position by a coil spring58. Accordingly, the balls56,56are engaged with a pair of retaining grooves60,60provided in a front-rear direction on the outer periphery of the tip tool T to retain the tip tool T and prevent the tip tool T from rotating with respect to the distal end portion55. When the operation sleeve14is retreated against the biasing of coil spring58, the lock ring59also retreats to release the push to the balls56,56, thus enabling the tip tool T to be inserted and removed.

In the distal end portion55, a metallic resistance ball61as a resistor having a diameter smaller than that of the ball56is disposed ahead of the upper ball56. The resistance ball61is configured to appear to the axial center via a through hole62drilled in the radial direction up to the distal end portion55. As also illustrated inFIG. 7, a C-shaped leaf spring63is externally mounted on the outer periphery of the distal end portion55at a position of the resistance ball61. In this externally mounted state, a small hole64provided on an end portion of the leaf spring63is fitted to the resistance ball61from the outside to push the resistance ball61to a projecting position partially projecting from the through hole62to the axial center. Accordingly, in the normal striking illustrated inFIG. 6, the resistance ball61abutting on the outer peripheral surface of the inserted tip tool T retreats outside in the radial direction against the biasing of the leaf spring63, pushing the tip tool T with constantly applying the resistance. A washer65is externally mounted on a front side of the leaf spring63to restrict the forward movement of the leaf spring63.

On the other hand, when the push-in operation is performed on the switch lever16in the non-striking state where the tip tool T is not pushed against the surface to be processed, as illustrated inFIG. 8, the first striking (no-load striking) with the striker22moves the intermediate element23forward from the retreated position and also moves the tip tool T forward. At this time, the tip tool T advances in a state where the resistance is applied by the resistance ball61. Thus, the momentum of the forward movement is reduced, and the bounce after the balls56,56collide with rear ends of the retaining grooves60,60as inFIG. 8reduces. Even if the balls56,56bounce, at the position where the balls56,56abut on the rear ends of the retaining grooves60,60, the resistance ball61relatively moves to the front end of the retaining groove60to return to the projecting position. Accordingly, the resistance ball61is engaged with the front end of the retaining groove60from the rear, so that the retreat of the tip tool T is elastically restricted here and the tip tool T does not return to the retreated position. Therefore, the subsequent no-load striking is prevented.

Further, in the hammer drill1A in the above-described modification example, the resistance ball61(resistor), which is configured to abut on the tip tool T in the non-striking state to apply the resistance to the front-rear move of the tip tool T, and the leaf spring63(biasing member), which biases the resistance ball61to a side of the tip tool T, are disposed on the tool holder10. Thus, the momentum of the tip tool T that advances with the no-load striking can be reduced to restrain the bounce, thereby preventing the subsequent no-load striking.

Especially here, the resistance ball61is disposed at a position where the resistance ball61abuts on the retaining groove60of the tip tool T that has advanced in the no-load striking to restrict the rearward movement of the tip tool T. Thus, the resistance can be easily applied to the tip tool T using the retaining groove60, ensuring effective no-load striking prevention.

In above-described modification example, the ball is employed as the resistor. However, a roller that is formed long in a front-rear direction may be employed, or a pin shape as in the prior form may be employed.

Here as well, the number of resistors is not limited to one, and a plurality of resistors may be concentrically disposed on the distal end portion. As the material of the resistor as well, for example, the ceramic and the hard resin can be employed other than the metal.

Furthermore, the biasing member is also not limited to the leaf spring, and for example, a wire wound around the distal end portion and a plate spring that is not wound around the distal end portion can be employed. The biasing member may be housed in a depressed groove formed on the outer periphery of the distal end portion.

In the above-described modification example, respective resistors are disposed on a side of the intermediate element and a side of the tip tool to enhance a no-load striking prevention effect. However, insofar as a desired no-load striking prevention effect is obtained, the resistor is allowed to be disposed on only the tip tool side without the resistor on the intermediate element side.

Besides, commonly in the above-described configuration and modification example, for the structure of the hammer drill as well, the resistor and the biasing member can be employed, even though the striking mechanism has a structure where an arm is swingably disposed on a boss sleeve provided on an intermediate shaft parallel to the tool holder via a swash bearing whose axis line is inclined such that a piston cylinder coupled to the arm is moved forward and rearward. An orientation and a type of the motor are not limited to those in the above-described configuration. A DC machine on which a battery pack is mounted may be employed not an AC machine.

Furthermore, the impact tool is not limited to the hammer drill, and an electric hammer including only the striking mechanism is also applicable to the disclosure.